Scotland’s Dotterel: still hanging on

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Dotterel brooding chicks

Within the UK, the Dotterel now only breeds on plateaux in the highest Scottish mountains, restricted by habitat that is more commonly found in the arctic or arctic-alpine regions. 

As soon as climate change became apparent, the Dotterel turned into a focal species for ornithologists who were interested in how species would be affected by climate heating. Their fate seemed to be sealed; put simply, there is nowhere colder in Britain to which to retreat when faced with changing habitats and/or breeding conditions.

A 2020 paper by Steven Ewing, Alistair Baxter and colleagues explores the potential ways that changing environmental conditions may be driving the Dotterel’s decline.

Life history

Scottish Dotterels don’t actually spend much time in Scotland, with most birds arriving in early May and leaving within three months. The large part of the year is spent in North Africa, and the plains to the northwest of the Atlas Mountains in Morocco seem to be a particularly important wintering grounds for Scottish birds. Migration north and south appears to be direct, with few European reports of ringed birds in spring and autumn. There is some evidence that Dotterel move further south within North Africa as winter progresses (Whitfield et al 1996), perhaps responding to rainfall patterns.

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In May, the numbers of males and females on Scottish breeding sites are roughly equal but many females leave their males sitting on a first clutch of eggs and then depart, leading to an observed drop in sex ratios to about 10:1. Females ringed in Scotland have been spotted breeding with Norwegian males later in the same season and this onward movement to areas with later snow-melt may well be a normal pattern. Indeed, many Dotterels seen on passage in May, often on traditionally used fields or mountain tops south of the Scottish Highlands, may loop north, passing through Highland nesting haunts and then heading northeast into Scandinavia.

A species in decline

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Alistair Baxter points to a Dotterel nest that’s right next to a path following the line of a ridge

Dotterels in Britain are at the south-western limit of the species’ global range. They breed almost exclusively in arctic-alpine habitats above 750 m, particularly on Racomitrium moss-heaths that are so characteristic of the flatter topped mountains. These habitats are of high conservation concern, with a tapestry of nationally-rare alpine and arctic plant species.

Scottish Dotterel have been well-studied for over eighty years, a process that was started by Desmond Nethersole-Thompson in the 1940s (detailed in his classic monograph The Dotterel, 1973) and has involved the authors of the Global Change Biology paper since 1987. Some of the areas featured in this paper were studied by Nethersole-Thompson.

An earlier WaderTales blog (Dotterel numbers have fallen by 57%) suggested a number of possible reasons for declines – habitat changes, increased predation and increased disturbance in the Scottish Highlands, compounded by issues affecting the wintering population in North Africa. In the 2020 paper, Ewing et al look in more detail at the potential roles of these changes

Climate and habitat change in Scotland’s mountains

Mountains in Britain are subject to a range of environmental drivers of change that may potentially influence Dotterels, but the logistical challenges presented by working in these environments means that there is rarely good data documenting these changes. This study focuses on snow cover and nitrogen deposition.

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The amount of snow-cover is important for cold-adapted species of plants and animals; it insulates the ground in winter and slows up warming in spring, thereby creating a relatively stable environment.  Potential consequences of changes in winter snow-lie for alpine birds might include:

  • A longer growing season for plants, with taller vegetation that reduces the suitability of these areas for species that favour shorter swards.
  • Fewer snow patches, around which Dotterel feed, perhaps also leading to a reduction in peak insect abundance that may not match feeding requirements of chicks.

blogpic nestLots of research carried out in the UK shows that nitrogen deposition is an important driver of upland vegetation change.  Higher deposition of nitrogen tends to result in a reduction of alpine specialist plants, including species of mosses that form key breeding habitats for Dotterel.

The earlier WaderTales blog (Dotterel numbers have fallen by 57%) suggested other possible reasons for Dotterel declines on the breeding grounds, including increased predation and increased disturbance in the Scottish Highlands. While these potential drivers of change could not be tested, due to a lack of data, they are considered in the paper’s Discussion.

Study system

The data that lie at the heart of the Global Change Biology paper have been collected over three decades. Two different but complementary data sources were used in the study.  Firstly, Dotterel were counted at between 128 and 198 alpine sites in the UK during three national surveys in 1987-88, 1999 and 2011.  These censuses focused upon suitable breeding habitats, especially Racomitrium heath, with the latter two surveys successfully covering more than 50% of identified breeding areas.  Secondly, between 1987 and 1999, a smaller cohort of alpine sites were surveyed with far greater frequency (between 40-60 times) as part of SNH’s Montane Ecology Project, where the aim was to study the Dotterel’s breeding ecology in far more detail. The 2020 paper contains detailed information about site use and the parameters that were measured/assessed (elevation, slope, area, snow cover, nitrogen deposition, summer temperature etc.)

blogpic surveyEach site visit involved a lot of climbing, so many of the sites were visited only once per season, with more frequent visits to just 15% of the sites. Having accompanied Phil Whitfield (one of the authors) up one mountain, on one day, I have huge respect for the effort that each data-point represents.  Once up on the tops, observers covered the study areas thoroughly, passing within 100 m of every point and scanning frequently. This has been shown to provide a good count of breeding males.

The authors used their data to investigate whether key potential drivers of environmental change in Scottish mountains (snow-lie, elevated summer temperatures and nitrogen deposition) may have contributed to the population decline of Dotterel.  They also consider the role of rainfall on the species’ wintering grounds in North Africa. The key questions they address are:

  1. Is there evidence of an uphill shift in the elevation of the Dotterel’s breeding range during the study period (1987-2014)?
  2. Are changes in the density or site occupancy of breeding male Dotterels associated with the size, connectedness or topographical aspect of alpine sites?
  3. Does spatial variation in atmospheric nitrogen deposition account for variation in density or occupancy of breeding males at alpine sites?
  4. Are patterns of snow cover or late summer temperatures associated with density or occupancy of male Dotterels at alpine breeding sites?
  5. Do densities of breeding male Dotterels on alpine sites vary with conditions on the North African wintering grounds, as reflected by winter rainfall?

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What has changed?

The results are presented in two ways. Data from the period of intensive studies, between 1987 and 1999, are used to try to understand factors influencing annual changes in the number of nesting males. Examination of changes between 1987-90 and 2011-14 gave some indication of factors affecting longer-term trends – something that is important to understand when Dotterel can live for at least ten years.

Densities of breeding male Dotterel in mountainous regions of Scotland declined between 1987 and 1999 and, over the longer-term, site occupancy fell from 80% in 1987 to only 36% in 2014. Densities of breeding males declined disproportionately from lower-lying sites, which resulted in the Dotterel’s breeding range retreating uphill at a rate of 25 m per decade.

Geographically isolated sites appear more likely to lose breeding Dotterel. This makes sense; playback studies in Russia have shown that passing flocks of Dotterel respond to calls, suggesting that birds will be attracted to already-occupied locations.

Settlement patterns were linked to snow-cover.  Generally, Dotterels appear to prefer to settle on higher sites, but late-lying snow at higher elevations appears to deprive them of suitable breeding habitat.  Rather than delay nesting, it seems that these birds then choose to move to lower snow-free sites to breed. Long-term changes in snow cover are poorly documented in high-elevation habitats in Scotland, so it is difficult to know whether the substantial declines observed for Dotterel in recent decades reflect systematic changes in snow-lie.

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Nitrogen deposition was shown to be negatively associated with densities of males nesting at lower and intermediate elevations.  The primary impact of nitrogen deposition on Dotterel is likely to be via effects on the species’ favoured Racomitrium moss-heaths, with greater nitrogen levels increasing the rate of moss decomposition and favouring accelerated grass growth.  This presumably results in these habitats becoming increasingly unsuitable for breeding Dotterel.

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Will this chick makes it to Morocco? If it does, how will the conditions it experiences in the non-breeding season affect its probability of return to Scotland?

High rainfall in North Africa seems to lead to higher densities of breeding male Dotterel two springs later, suggesting that wintering ground conditions can potentially influence population dynamics of this alpine-breeding bird.  Similar positive impacts of North African rainfall have also been seen in Ring Ouzels that breed in the UK (Beale et al. 2006).

Dotterel inhabit open farmland and sub-desert steppes in North Africa, where seasonal rainfall brings a flush of vegetation growth and insect abundance. Higher winter rainfall may increase prey availability and Dotterel survival rates but that would be reflected in the arrival numbers in the next spring. The lag of an extra year suggests that low rainfall levels may mostly affect young birds, perhaps delaying recruitment of some Dotterels until their second breeding season.

Conclusions

blogpic juvvyPopulation declines and site abandonment by Dotterel in Scotland during the last three decades have largely occurred at lower elevations, fitting with the traditional idea of climate change limiting the available climate space for alpine breeding species. However, this study found relatively limited evidence that the decline in the breeding population is being driven by climatic factors on the breeding grounds.

Snow cover does seem to influence year-to-year variation in the species’ elevational distribution in Scotland, potentially because a smaller population may now be increasingly settling on higher sites that perhaps were previously unavailable, due to extensive snow cover.  There was also some evidence that greater nitrogen deposition reduced breeding densities of Dotterel at low to intermediate elevations, perhaps by decreasing the suitability of Racomitrium moss heath breeding habitats.  It is also possible that there may have been a redistribution of birds, with newer generations moving further north, to more suitable sites in Norway. (There is a WaderTales blog about this sort of Generational Change mechanism in waders, focusing on Black-tailed Godwit).

Given that Dotterels spend so little time in Scotland, a big gap in our understanding is what is happening in Morocco, where adult Scottish Dotterel spend three-quarters of the year and where young birds may also spend their first summer. How are factors such as rainfall and land-use (particularly farming methods) affecting Dotterels? Might changes in these areas affect other species of migrant that leave northern Europe at the end of the breeding season? Perhaps conservation scientists need to head south for the winter to find out?

Read more in the paper

Clinging on to alpine life: investigating factors driving the uphill range contraction and population decline of a mountain breeding bird. Steven R. Ewing, Alistair Baxter, Jeremy D. Wilson, Daniel B. Hayhow, James Gordon, Des B. A. Thompson, D. Philip Whitfield & René Van der Wal. Global Change Biology.

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GFA in IcelandWaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on published papers, with the aim of making shorebird science available to a broader audience.

@GrahamFAppleton

 

Migration of Scottish Greenshank

pic12 ringedIn the days of big data sets and complex analyses, it is pleasing that local, focused studies can still answer specific gaps in our understanding of migratory behaviour. Ron Summers and his colleagues have responded to a comment by Patrick Thompson, at the end of his contribution to The Migration Atlas, published by BTO in 2002: “… it is of major concern that we know so little about where Scottish birds [Greenshank] go once they leave the breeding grounds.” With a small number of geolocators and a few dozen plastic colour-rings, they are now able to answer this implied question, in a 2020 paper in Bird Study.

On the edge of range

Greenshank (or Common Greenshank) breed across the boreal zone of the Palearctic, from eastern Siberia in the east to Scotland in the west. The map below, produced by BirdLife International clearly shows that Scottish Greenshank lie at the southern and western extremes of this distribution. The species is even more widely distributed outside the breeding season; you can hear their three-note tew-tew-tew calls from New Zealand to the west of Ireland.

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Scotland holds a small population of Greenshank, estimated at 1440 pairs in 1995 (Hancock et al. 1997) but revised to be 1100+ in the latest population estimate in British Birds. This is a tiny part of a global population estimated as between 440,000 and 1.5 million individuals (Wetlands International). The lack of precision implicit in this large range is unsurprising; Greenshank tend to occur in small numbers in most of their wintering locations, not conveniently collecting in large flocks, such as Redshank or Knot.

pic4 breed mapThe northwest corner of mainland Scotland, together with the northern isles of the Outer Hebrides, are the main focus of the UK distribution, as is clear in the map showing relative abundance, taken from the BTO’s MapStore, based on Bird Atlas 2007-11 (BTO, BirdWatch Ireland & SOC).

The Greenshank is far more widely spread across the British Isles in the winter. The three maps below, also based on data from Bird Atlas 2007-11 show a growth in the number of inland and east-coast sightings between 1981-84 (left) and 2007-11 (middle), with the highest densities in west coast sites in Ireland and Scotland.

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The Greenshank of Tongue

pic7 breed adultThe sound of a calling Greenshank takes me back to an Easter holiday that involved cycling into the wind (and odd snow flurry) along the A roads of the north coast of Scotland. These elegant waders are very much at home in this terrain of bogs, moorland and rocky outcrops. The study area for the project at the heart of this blog was near Tongue, two-thirds of the way from John o’ Groats, in the east, to Cape Wrath, in the west.

Between 2010 and 2015, twenty-four breeding Greenshank were trapped at the nest, by laying a mist-net over them. All were colour-ringed (most uniquely) and geolocators were attached to twenty of them. In most cases, feather samples were taken to determine gender. As many as possible of the geolocators were retrieved when the birds returned to breed, by again catching birds on their nests but one was recovered by a French hunter and another when a bird was recaptured in North Wales.

pic11Tongue

Stories from colour-rings

Prior to this study, the only ringing recoveries of Scottish-breeding birds refer to a chick ringed at Forsinard (Sutherland) on 6 June 1926 and shot in Ireland four months later, and a chick ringed in Perthshire in June 1974 and shot in northwest France that September. As both of these were autumn records, the young birds could still have been on migration when shot. The first definite winter location was established when an adult colour-ringed in Sutherland in 2010 was found to winter in Essex (eastern England).

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Ten of the colour-ringed birds from Tongue have been seen away from the breeding grounds: two in Scotland, five in Ireland and one each in Wales, northwest England, southeast England and southwest France. These movements represent migrations of between 530 km and 1560 km, which must seem unimpressive to a Greenshank that flies 10,000 km to reach southern Australia. Scottish colour-ringed birds have been seen on staging areas but once they arrive in their wintering areas in late June and July, they don’t move again until the following March or April.

In the case of one pair of Greenshank, both male and female were ringed and resighted. The male was in Wales and the female in France. If you have read Black-tailed Godwits: the importance of synchrony, this will come as no surprise!

Additional data from geolocators

pic10 scanColour-rings cannot really establish whether migration is non-stop or staged, just because sighting probability is low. By using geolocators, which collect data on the timing of dusk and dawn, it is possible to work out where individuals go between one year and the next – as long as you can re-catch individuals wearing geolocators! Seven geolocators were recovered (five by recapture of breeding birds, one shot in France and one recaptured at its Welsh wintering site – see image alongside). One geolocator did not work but there was sufficient information from the other geolocators to show that:

  • Geolocations for four birds indicated that they spent the winter in Ireland (but geolocators do not give precise information and one of these birds was actually seen (and subsequently caught) in North Wales)
  • One bird spent the winter in France (proved by being resighted and later shot there)
  • One tagged bird was recorded as being in Ireland in September, after which data collection ceased
  • Median departure date from northern Scotland was 16 July
  • Median arrival date in final wintering locations was 17 July
  • One Irish-wintering bird staged for two days in southwest Scotland
  • The French wintering bird appeared to spend a day in southern Ireland on its way south and to stop off in northern France on its way north.

Context and conclusions

pic6 chickAlthough the Summers et al Greenshank study only involves a small number of birds, it seems that Scottish birds do not migrate far, with none seen outwith Ireland, Britain or France.  Further, the data from the geolocators, which do not rely on birdwatchers spotting the birds, provided no evidence of birds going further south than France.

Although the migration distances were relatively short, there was some staging during southward and northward migrations.  For most birds, there was no staging and they could have accomplished the migration distance to Ireland or Wales (500-700 km) in about 10 hours, if flying at 60 km per hour (Alerstam et al. 2007).

The size of the wintering populations of Greenshank in Ireland, Great Britain and France are estimated as 1,265, 810 and 200, giving a total population of about 2,300 in these countries.  The breeding population in Scotland in 1995 was estimated as being between 1,100 and 1,790 pairs. Adding in chicks might mean that 4,000 birds are on the move each autumn. Although this value is higher than the numbers counted in Ireland, Britain and France in winter, the authors suggest that the two values are not so far apart as to discount the conclusion that the majority of birds from these wintering populations are derived from the Scottish-breeding population.

Winter visitors and passage migrants

pic1 BTO mapThe map alongside shows the movements of ringed Greenshank to and from Britain & Ireland, as extracted from the BTO’s online ringing report on 20 March 2020. There is evidence of the classic leap-frog migration, with individuals that breed further north spending the winter months further south. British breeding Greenshank may not move very far but many birds from Norway, Sweden and Russia spend time in Britain on their way to western African countries such as Ghana and Ivory Coast. Spring records in Italy suggest some birds might take a more easterly route on their way north.

Data from a UK-based colour-ring and tagging programme, coordinated by Pete Potts of Farlington Ringing Group, are being analysed. Initial findings suggest that a single estuary can host birds from a range of breeding locations. Some passage birds stay to complete moult but others just fatten and move on. We should soon know more about the relative importance of these British stop-over sites to western European Greenshanks.

pic8 bandwTo read the paper

The full story is available in Bird Study: 

Scottish-breeding Greenshanks Tringa nebularia do not migrate far. Ron Summers, Nick Christian, Brian Etheridge, Stuart Rae, Ian Cleasby and Snæbjörn Pálsson. Bird Study. March 2020.

The study was a Highland Ringing Group project, supported by the Scottish Ornithologists’ Club Endowment Fund.

More about migration

If you found this blog interesting, here’s a selection from the WaderTales catalogue that may also appeal. The first two articles reveal the results of a local study of Green Sandpipers that spend the winter in Hertfordshire.

In the next two blogs, you can read how migration patterns vary in Oystercatchers, depending upon how far north birds breed, the locality in which they nest and the obstacles that lie in the way if they undertake migratory journeys.

And this blog is all about ‘happenstance’, the seemingly random processes that presumably determine why Sanderling from the same small part of Greenland may fly as far as South Africa or just to Scotland:

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GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.

@grahamfappleton

 

Black-tailed Godwits are on their way home

bg topAs I write this, at the start of March 2020, spring is on its way – and so are limosa Black-tailed Godwits. Many have flown north from wetlands and rice-fields in West Africa and are now fattening and moulting in a small number of sites in Portugal, France and Spain. The vast majority are heading for the Netherlands but a few will ‘bear left’ and end up in East Anglia.

The biggest spring flocks of limosa Black-tailed Godwits are found on the Tagus (or Tejo) Estuary, in Portugal, a site that is under threat from a planned airport development. Swirling flocks of up to 80,000 birds create a wildlife spectacle that attracts an increasing number of tourists. Among these ranks of telescope-wielding birdwatchers is a small band of dedicated colour-ring readers from the Netherlands working on a University of Groningen / Global Flyway Network project. They are looking for marked Black-tailed Godwits (Grutto in Dutch) that are part of their conservation science project; some of these Grutto are old friends, others will have been ringed as chicks and are now heading north for the first time.

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This year, the Dutch team working in Portugal in mid-February spotted ten Project Godwit birds – Black-tailed Godwits that belong to the tiny and highly threatened population that breed in the Ouse and Nene Washes. An increasing number of these sightings of English birds are of ‘head-started’ godwits; birds that started life as eggs in nests on the RSPB’s Nene Washes reserve and were then hatched in incubators and reared in captivity at the Wildfowl & Wetland Trust’s Welney reserve. You can read more about head-starting here.

Before telling some fascinating individual stories, here’s a quick reminder that conservation operations in The Netherlands, the UK and elsewhere might be jeopardised by a plan to build a second airport for Lisbon, within the Tagus Estuary – one of the top wetlands in Europe and a critical stopover site for limosa godwits.

Birds v Planes

bg petitionMillions of euros – and a smaller number of pounds – are spent each year in support of the dwindling populations of limosa Black-tailed Godwits that breed in the Netherlands, here in the UK and in other countries within Europe. Much of the money is helping ‘meadow birds’ in general but there are specific interventions to protect godwit nests and chicks during farming operations in the Netherlands and to boost chick production in England. These huge (and often expensive) conservation efforts are potentially being threatened by a plan to build the so-called Montijo Airport in the heart of the Tagus Estuary. This is where up to 80,000 Black-tailed Godwits gather in spring and several thousand spend the winter. You can read more about the planned airport and the importance of the area to migratory waders and other waterbirds in Tagus estuary – for birds or planes?

You can support the Dutch initiative to stop the new airport by signing the petition being organised by Vogelbescherming, the BirdLife partner in the Netherlands. Link here.

Last chance for England’s breeding Black-tailed Godwits

When Project Godwit started in 2017, there were only 38 pairs of Black-tailed Godwit breeding in East Anglia, mostly on the Nene Washes, with a small number on the Ouse Washes. Despite huge efforts by conservation organisations, and the RSPB in particular, productivity was consistently very low. Predation and flooding were the main challenges; there was a real prospect of ageing birds failing to raise enough youngsters to maintain the viability of the population. While work continued to create alternative flood-free breeding areas at the Ouse Washes and to tackle predation issues, these godwits needed a boost. That’s where head-starting comes in; by removing first clutches, incubating the eggs, raising the chicks and releasing them back onto the Nene and Ouse Washes, once fledged, it proved possible to greatly increase the number of young birds that headed south for the winter.

Sep2019

At the start, there was no guarantee that head-starting would work. The first WaderTales blog about Project Godwit was a plea for birdwatchers to look out for colour-ringed, head-started chicks, the second asked whether the released chicks would be able to find their way back to East Anglia and the third celebrated early successes.

  1. Special Black-tailed Godwits
  2. Site-fidelity in Black-tailed Godwits
  3. Head-starting success

The success of these special head-started Black-tailed Godwits has been enjoyed by millions who watch the BBC’s Springwatch series and thousands of visitors to the WWT centre at Welney. In addition, individual godwits have played starring roles in newspaper and magazine articles and on local television news programmes.

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Migration

bg SenegalOne of the big take-home messages from Project Godwit is that head-started chicks, released back on the Ouse and Nene Washes, soon mix with wild-reared birds and adults.  Information collected so far suggests that head-started birds follow similar migration patterns to the wild godwits.  Most limosa Black-tailed Godwits travel south to countries in West Africa, especially Senegal, and then fly north after Christmas, to Portugal and Spain.  Some may make another stop in France, before reaching their territories. An increasing proportion of the main Dutch population is now wintering in Europe (Should Black-tailed Godwits cross the Sahara?). Dutch and Iberian researchers are using satellite tracking to monitor day-to-day movements (King of the Meadows)

Birds on the Tagus in 2020

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Black-tailed Godwits feeding in a Tagus rice-field

Some limosa Black-tailed Godwits spend the winter on the Tagus but big flocks do not start to build until the start of the new year, as birds return from Africa. The ten colour-ringed Project Godwit individuals that were seen by the Dutch team between 2nd and 10th of February 2020 were a mixture of old friends and birds that had not been seen on the rice fields before. Flocks of 30,000 or more Black-tailed Godwits can descend upon a single rice-field, post-harvest, to feed on spilt grain and invertebrates. It is not easy to spot colour-ringed birds in the melee of legs, as birds wade through the water, and it is very likely that there were many more Washes birds that were not spotted. The ten Project Godwit birds were seen alongside hundreds being studied by Dutch conservation scientists. So, which individual godwits were seen?

Class of 2017

Two head-started chicks from the first year of the project were seen in February 2020. One of them was YG-GL(E) or Remi (click on her name to read her story), who starred in the WaderTales blog Site-fidelity in Black-tailed Godwits. We know that she is one of the majority of Black-tailed Godwits that fly to West Africa because she was also spotted in Senegal in November 2019. A total of 24 head-started birds were released in the summer of 2017 and six of them have now been seen on the Tagus.

bg remi in cage

Class of 2018

bg HurricaneIn the summer of 2018, 38 head-started chicks were released and two of them were seen this February in the Tagus rice-fields. One of these was WG-WL(E) or Hurricane, a bird that spent his first summer near Valencia in Spain before departing in mid-June. Some Black-tailed Godwits fly north in their first spring but many do not. After months of Spanish sunshine, Hurricane may well have flown south with an early flock of post-breeding adults, moving through to West Africa in the late summer,  and that the Dutch team spotted him on his way back to the Washes. Two other head-started birds from the second year of the project have been seen on the Tagus, making a total of four.

Class of 2019

The 48 head-started birds from 2019 are still only a few months old. Some might be on their way back to the Washes but there were no sightings in early February. It has been suggested that birds that do migrate north to breed in their first year might be on a slightly later schedule, so perhaps later teams of Dutch observers might report one or more of these birds.

Wild chicks 2017-2019

bg ad chicksThe Project Godwit team try to ring as many as possible of the wild-reared chicks on the Nene Washes, so that they can compare their behaviour patterns to those of the captive-reared group. Two of the wild-reared birds have been seen on the Tagus; a chick from 2018 was reported in both 2019 and 2020, and a chick from 2019 was seen in the autumn of 2019.

Earlier chicks

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Two members of the Dutch team of colour-ring readers: Rienk Jelle Hibma & Teade de Boer

The RSPB has been studying Black-tailed Godwits for over twenty years. One of the very early chicks was spotted in the rice-fields this February. LG-RL(E) was ringed 21 years ago and she had previously been reported in the Tagus estuary in the springs of 2017, 2018 and 2019, and in the autumn of 2018. Black-tailed Godwits are known to live for up to 25 years.

Ringed as adults

RSPB researchers also ring adults by catching them on their nests. Four birds ringed in this way were seen on the Portuguese rice-fields in February 2020. Adding in four head-started chicks, and two chicks that was raised in the wild, this makes a total of ten birds from the Ouse and Nene Washes that are known to have visited the Tagus Estuary during this spring.

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There are two colour-ringed birds in this photograph

One that won’t be seen again

RY-OL(E) was ringed in 2002 and spotted in the Tagus in February 2018. She has been a key contributor to Project Godwit over the last few years, fledging two chicks in the wild in 2018 and three in 2019. Additionally, she provided four extra young godwits via the head-starting process in 2018. Her metal-ringed leg was recently found in a Peregrine nest in Brighton. Presumably she became a meal for a young Peregrine in the late summer of 2019.

Conservation importance of the Tagus Estuary

In February, the Tagus is thought to hold half of what is left of the Dutch population of Black-tailed Godwits, when up to 80,000 birds move around the estuary in huge flocks. Colour-ring reports and sighting probabilities suggest that around half of the Project Godwit birds, heading for the Ouse and Nene Washes, may also rely on the mud-flats and surrounding rice-fields in the early spring.

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Project Godwit has already given a terrific boost to the Black-tailed Godwits breeding in England, with the number of pairs up from 38 in 2017 to 45 in 2019, and it seems ridiculous that much of the good work could be put at risk if Montijo Airport is built. It is sad that a five-year project, that has involved over 20 dedicated RSPB and WWT staff , together with local volunteers and observers in the UK, Europe and Africa, might be in jeopardy.

Project Godwit has received major funding from the EU LIFE Nature Programme, HSBC 150th Anniversary Fund, Natural England, the Heritage Lottery Fund (through the Back from the Brink Programme) and Leica UK. The Dutch team of colour-ring readers in February 2020 was: Jan Vegelin, Kees de Jager, Egbert van der Velde, Rienk Jelle Hibma, Teade de Boer, Bob Loos & Jacob de Vries.  Their work is directed by Jos Hooijmeijer and funded by the University of Groningen and the Global Flyway Network.

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GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.

@grahamfappleton

Which Icelandic Oystercatchers cross the Atlantic?

blog ringed birdMost Icelandic Oystercatchers leave Iceland in the autumn, crossing the Atlantic and arriving in Ireland, the UK and mainland Europe. Despite much shorter day-length and colder conditions, 30% spend the winter in Iceland, as discussed in this blog (Mission Impossible).

A 2020 paper from Verónica Méndez and colleagues asks whether birds that stay in Iceland or cross the Atlantic differ in sex, body-size or breeding location (within Iceland) and whether birds behave differently in different years. Interestingly, they were also able to test whether there is assortative mating – do Oystercatchers that stay in Iceland pair with other stay-at-home birds?

Iceland’s Oystercatchers

Iceland lies at the northern edge of the breeding range of Eurasian Oystercatchers. The country supports an unusually high proportion of wintering Oystercatchers, given its latitude and winter temperatures (Þórisson et al. 2018), and this may be influenced by the trans-oceanic flight of at least 700 km that migratory individuals must undertake to reach the European wintering sites. Individuals that migrate or stay within Iceland could differ in body size, for example if size influences the capacity to survive adverse winter conditions. Females tend to be slightly larger, and thus any sex differences in migratory behaviour could potentially reflect differences in body size.

It would be easy to imagine a scenario in which Oystercatcher pairs try to breed as early as possible, as this could increase the number of potential nesting attempts, as discussed in Time to nest again, based on Morrison et al. 2019. Does this mean that stay-at-home birds pair off at the start of the season, before migrants arrive? Given that most birds will choose the same mate in successive years, what happens in mixed pairs if a resident is waiting around for a delayed migrant? Is divorce likely to occur, as discussed in the importance of synchrony for Black-tailed Godwits, and could this mean that mixed pairs are rare?

Colour-marks and isotopes

blog map of sightingsA huge amount of the evidence that was used to answer the questions posed by Verónica and her colleagues was provided by volunteer birdwatchers, who reported colour-ringed Oystercatchers in their wintering areas, in the period through to April 2018. There’s an impressive set of dots on the map alongside, from the north of Scotland through to Spain, and the number of sightings continues to rise. It’s perhaps unsurprising, given the direction of travel from Iceland, that there is a strong westerly bias to the distribution across the British Isles.

The sample size from colour-ring observations was not big enough to answer all of the questions posed above, especially relating to whether pairs mate assortatively. To provide one data-point, it’s necessary to know the winter locations of both members of the pair. Might feather isotope ratios provide some help?

Oystercatchers that winter in Iceland use a restricted number of coastal sites (as inland sites are frozen during winter) and forage on marine prey. Elsewhere in Europe, a much wider range of marine and freshwater resources is available, with birds readily moving between the shoreline and fields, golf-courses, football pitches and road-side verges. Previous studies have shown that terrestrial diets produce different carbon and nitrogen isotope ratios, based on salinity and trophic level of prey items.  Are differences in habitat use and diet of Oystercatchers reflected in carbon (δ13C) and nitrogen (δ15N) isotope ratios of feathers grown during late winter?

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Oystercatchers moult their chest feathers in late winter

The research team hoped that isotopic signatures from resighted colour-marked migrants and residents would be sufficiently different to be able to predict the probable wintering areas (Europe or Iceland) of marked birds not seen away from their breeding sites. If so, this would greatly increase the sample size, by enabling the combination of data from observations of colour-marked individuals with information on birds that could be assigned as Icelandic or European winterers using the isotopic composition of their feathers. They predicted that it would then be possible to:

  • Identify migratory strategies of individual Oystercatchers and explore whether the likelihood of migrating or staying in Iceland is related to gender, body size or breeding location.
  • Assess how consistent these individual strategies are between years.
  • Quantify spatial variation in the distribution of migrants and residents across the Icelandic breeding range.
  • Determine whether Oystercatchers mate assortatively in relation to migratory behaviour.

The work covered in this paper was conducted between 2013 and 2017. Full details of the study areas and methods are available in the paper – link below.

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Early nesting is not always a good idea – still incubating after sudden snow-fall

Migrant or resident?

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An Icelandic Oysterctaher spending the winter in Co. Sligo in Ireland

Of the 537 colour-ringed adults in the study, 58 were seen away from Iceland and 55 were shown to be resident in Iceland. Oystercatchers undertake a partial moult at the end of the winter period, when they grow new feathers on the neck and chest. The isotopic signature of a tiny piece of one of these feathers, taken from each adult at the time of ringing or recapture, was determined. The values of δ13C, which relates to habitat salinity, and δ15N, which relates to trophic level of diet, varied between residents and migrants but there was an overlap (details in paper).  There was enough of a difference, however, for it to be possible to allocate two-thirds of ringed birds that had not been seen in the winter period to the resident and migratory categories, with sufficient certainty, thereby increasing the sample size for other tests.

Consistency of migratory tendency

The 18 individuals that were observed in more than one winter were all consistent in migratory behaviour (10 residents and 8 migrants) and each was seen in the same specific location (Iceland or western Europe) in both winters. Where feather samples were taken in more than one year, there was no evidence of any bird changing its habitat or diet.

Factors influencing individual migratory programmes

Females and males were equally likely to migrate and there was no evidence that bigger (or smaller) birds were more likely to leave Iceland. Most Oystercatchers that winter in Iceland are in flocks in the west of the country, where the coast is warmed by the Gulf Stream. Unsurprisingly, westerly breeders were more likely to be resident than those in the south or northeast of Iceland (see figure below).

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Assortative mating

Vero and her colleagues were able to assign the migratory strategy to both members of the pair for 162 pairs (either by resightings or using predictions from isotopic signatures). Among these, 75 pairs (46%) were both migrants, 32 pairs (20%) were both residents and 55 pairs (34%) were mixed. The frequency of full-migrant, full-resident or mixed pairs varied significantly among regions, which was to be expected, given the differences in the likelihood of migrating from different parts of Iceland. There was no evidence of assortative mating; the likelihood of a particular individual pairing up with a migrant was as expected from the proportion of migrants in the area; it was not influenced by whether the particular individual was itself a migrant (see figure above).

To migrate or remain in Iceland

The consistency of adult migratory behaviour suggests that migratory strategy is determined in early life, and the regional variation in the frequency of migrants and residents may thus reflect variation in the conditions encountered by individuals during this life stage. As noted above, the frequency of residency is greatest amongst Oystercatchers breeding in the west of Iceland, which are the areas closest to the main wintering locations. Juveniles from the northwest and west are more likely to encounter these flocks of adult and sub-adult birds when moving south, than juveniles from the south, north-east and east, which are more likely to encounter migrating adults.

blog gen chThe regional variation in migratory strategy could arise through the influence of social cues, with juveniles adopting the behaviour of Oystercatchers they encounter and then recruiting back into their natal locations (more about this in Generational Change, focusing on Black-tailed Godwits). Birdwatchers across Europe will hopefully help to test this theory, by tracking colour-ringed juveniles during the early years of life. This is all part of a quest to identify the conditions that influence migratory behaviour and to understand the consequences, in terms of survival rates and productivity, of adopting different migratory traits.

Paper

Please click on the title below to access the paper:

Individual variation in migratory behavior in a sub-arctic partial migrant shorebird by Méndez V., Alves J.A., Þórisson, B., Marca, A., Gunnarsson, T.G., Gill, J.A.  Published in Behavioral Ecology (2020).  doi.org/10.1093/beheco/araa010 

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GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.

@grahamfappleton

 

Tagus estuary: for birds or planes?

blog samoucoA planned new airport that will serve Lisbon threatens the future of internationally important flocks of waders and other waterbirds. These same birds pose safety concerns for the passenger aircraft that will fly through the airspace that is currently reserved for them.

The development site of the proposed Montijo airport abuts the part of the Tagus/Tejo estuary that is designated as a Special Protection Area (SPA) and an Important Bird Area (IBA). This designation is based upon counts of 49,000 Black-tailed Godwits, 12,000 Dunlin, 6000 Avocet, 4500 Wigeon, 3300 Greylag Geese, 2000 Grey Plover and 1600 Greater Flamingos. That’s 23 tonnes of birds, representing just a few key species, before you add in gulls, Spoonbills and up to 6,000 Glossy Ibises. This blog focuses upon the importance of the Tagus/Tejo Estuary for just one of the species, the Black-tailed Godwit.

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The planning process

At first sight, turning the air force base in Montijo into a commercial airport looks like an obvious option, given that planes already take off and land there. However, the runway will need to be longer, there will have to be a vast new infrastructure and planes will be landing every few minutes, rather than during scheduled periods of military training. There will be some habitat removal, and it will be hard to avoid run-off of fuel and chemicals into the estuary, but the big problem will be disturbance of the flocks of birds within this IBA, as planes land and take-off and when airport employees frighten away flocks that are too close to the main flight-paths. Each time a flock of birds takes to the air, a large amount of fuel is burnt – as fat laid down for migration is wasted.

blog flamingoPlanes and birds do not mix, as we saw on 15 January 2009, when US Airways Airbus Flight 1549 landed on the Hudson River after an encounter with Canada Geese. How many Greater Flamingos will it take to stop a jet engine? Each one weighs about three kilogrammes and there are 1600 on the SPA, many within a few hundred metres of the airport site.

Around the world, there have been many bird/plane incidents, some causing significant loss of (human) life, which explains why there’s not a ‘Boris Island Airport’ in the Thames Estuary. History suggests that bird-strike risks are underplayed at the planning stage but have to be coped with later. Once the airport is operational, it is likely that nests will be removed and attempts will be made to disperse flocks through disturbance and shooting.

Icelandic Black-tailed Godwits

The Tagus is particularly important for Black-tailed Godwits. Although the published count, associated with the designation of the estuary, is 49,000, it is agreed that the maximum late-winter number for the estuary and surrounding rice fields is now 70,000 or more, which includes birds of both the islandica and limosa races.

mapThere are Black-tailed Godwits on the Tagus during every month of the year. Numbers are lowest in the summer, chiefly comprising young islandica birds that do not travel back to Iceland in their first spring. Adults arrive back from Iceland between July and November, the later birds having stopped off to moult in sites such as the Wash (Eastern England) and coastal France. Numbers drop again as early as January, when adults move to the Netherlands and England, to fatten up for the trip back across the Atlantic to Iceland. There is a blog about this ‘overtake manoeuvre’ and the advantages it confers.

Given that islandica Black-tailed Godwits can spend the winter anywhere between Scotland and the south of Spain, it could be argued that disturbance on the Tagus, to try to disperse flocks, would be no big problem, as there are other places for individuals to spend the winter. Two things are wrong with this theory. Firstly, as was described in Generational Change, individual Black-tailed Godwits are creatures of habit, typically using a suite of about four non-breeding sites during their entire lives. If a Black-tailed Godwit is on a patch of mud in December one year then it will be back there the next year, and possibly for the next twenty.

blog RedshankThere is no reason to believe that Black-tailed Godwits are unique in being site-faithful. In the WaderTales blog called A place to roost there is a description of the consequences of site removal for Redshank in Cardiff Bay. Birds displaced by the flooding of the bay had much lower survival rates in the next year and in subsequent years than other Redshank with which they shared their new winter homes. This illustrates the second point; even though these Redshank were only forced to move a few kilometres, they were still severely disadvantaged.

Limosa Black-tailed Godwits

The Tagus really comes into its own during the late winter, as limosa Black-tailed Godwits pour into the area, en route to their breeding grounds in continental Europe. An increasing number of the limosa subspecies now spend the winter on the estuary and in surrounding fields but numbers grow rapidly in January, as others join them from sites as far south as Guinea, in West Africa. On the Tagus, they moult into summer plumage and build up fat reserves that will fuel flights to The Netherlands and surrounding countries, and prepare them for the breeding season that lies ahead. A favourite rice field may hold up to 70,000 Black-tailed Godwits in late February, which includes half of what’s now left of the Dutch breeding population. This is also where many of the birds that are heading back to the Nene and Ouse Washes of Eastern England fuel up for the final leg of their journeys home. Several of the Project Godwit head-started birds (youngsters raised from eggs and released when just about to fledge) have been seen on the Tagus in February.

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To watch vast feeding flocks of Black-tailed Godwits, or their swirling aerial displays, when disturbed by a hunting Peregrine, is an amazing experience – a highlight for locals and for visiting birdwatchers, who holiday here in late winter and early spring. It’s especially impressive to watch the godwits at dusk, when clouds of Glossy Ibis create a backdrop to the action, as they move off the fields and cross the IBA to roosting islands on the far side of the estuary.

blog take offAs indicated earlier, The Tagus Estuary is designated as an EU Special Protection Area because of its crucial role in the lives of a suite of species, just one of which is the Black-tailed Godwit. Over the last few years, the average peak godwit numbers on the Tagus and Sado Estuaries in Portugal have risen from 44,000 to 51,000, at the same time as the breeding population of the subspecies has dropped rapidly (see this WaderTales blog about 75% drop in Dutch numbers). The Portuguese increase has coincided with a rapid decline in spring totals in Extremadura (Spain).

Without colour-rings, it might be assumed that individual Black-tailed Godwits have changed their migration routes, suggesting a flexible response to changing conditions. This is not the case. In their paper, Generational shift in spring staging site use by a long-distance migratory bird, Mo Verhoeven and colleagues show that nearly all of the older birds stick to the routes that they know, with young birds establishing routes that are more likely to include the Tagus and Sado Estuaries. Western Portugal has become vitally important to limosa Black-tailed Godwits, a subspecies that is in huge trouble and upon which millions of conservation Euros are being spent in The Netherlands and elsewhere.

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What next?

The Portuguese Environmental Agency (Governmental institution) has given the go-ahead for the development of the airport at Montijo, despite robust arguments from researchers and conservationists about the inevitable effects on the IBA, and errors and limitations they have identified within the Environmental Assessment Study. There are also concerns about flooding risk, air pollution and other issues that seem not to have been fully assessed.

AEWASPEA, the Portuguese BirdLife partner, together with wader researchers who have studied waterbirds in the Tagus for decades, have submitted a request to the UNEP African-Eurasian Migratory Waterbirds Agreement (AEWA) to open an Implementation Review Process, to help Portugal to ensure that it complies with its obligations as a signatory to the treaty. The approach to AEWA is particularly appropriate for Black-tailed Godwits, as AEWA has already published a Single Species Action Plan to try to support efforts to restore populations of the rapidly declining limosa subspecies.

Black-tailed Godwits may be the most numerous of the key waterbird species for which the Tagus/Tejo Estuary is designated but let’s not forget the next most numerous six: 12,000 Dunlin, 6000 Avocet, 4500 Wigeon, 3300 Greylag Geese, 2000 Grey Plover and 1600 Greater Flamingos.

flamingo and ibis

Key conservation point

The most important conservation fact to bear in mind is that, as has been shown for Black-tailed Godwits, individual birds tend to be remarkably inflexible. Circumstances determine the migration pattern in the first year of life and, if a bird survives, it will continue to do the same things in subsequent years. Building an airport and then trying to reduce plane/bird interactions will quite probably affect the quality of the IBA for waders and other species. Individuals are unlikely to move elsewhere; they are more likely just to try to cope with altered circumstances. Habitat loss and disturbance on this scale are very likely to result in high levels of mortality and declines in the numbers of birds using this critically important site on the East Atlantic Flyway.

Petition

The Black-tailed Godwit is the Dutch national bird. The BirdLife partner in the Netherlands, Vogelbescherming, has launched a petition to register Europe-wide concern about the Portuguese decision to build the new airport. Not only will the new airport be a disaster for the East Atlantic Flyway, it also sets a precedent for developments affecting other Europe wetlands. Please click here to sign.

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GFA in Iceland

Graham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

Red Knot pay the price for being fussy eaters!

jean-hall_36310664056_oIn a fascinating comparison of weight gained by Red Knot and Ruddy Turnstone during spring migration in Delaware Bay, on America’s east-coast flyway, Anna Tucker and colleagues show that Knot are far more vulnerable to annual variations in their main food supply than more flexible Turnstones, which target the same food if it is available. Given that changing weather patterns, associated with a warming climate, are expected to make resource availability harder to predict, the authors suggest that populations of migrant shorebirds (waders) that rely on a specific resource being available at the right time are likely to be more vulnerable – as has become apparent for Delaware Bay Knot.

Feast on the beach

Spring shorebird migration in Delaware Bay is largely fuelled by the superabundance of the eggs of horseshoe crabs. Some of the numbers associated with crabs, eggs and migratory waders are amazing!

  • Horseshoe crabs have been around for 400 million years.
  • Each spring, hundreds of thousands of horseshoe crabs swim to Delaware Bay, where the females spawn in the sand along the tidelines of Delaware and New Jersey.
  • Historically, horseshoe crabs were collected, ground up and used as fertilizer. They are still harvested for use as bait and to be bled for the pharmaceutical industry.
  • Each female crab can lay 100,000 eggs, burying them in clumps in the sand above the high tide line, over the course of a few nights.
  • Disturbance by other females and wave action brings eggs to the surface, where they become readily available to birds.
  • In a good year, egg densities on beaches can reach 800,000 per square metre, in hot-spots.
  • Over half a million shorebirds still visit Delaware Bay each spring. This number used to include 100,000 Knot but peak counts are now generally much lower, in the region of 25,000.
  • A Knot can eat 25,000 eggs a day and double its weight in two weeks.
  • Horseshoe crab eggs fuel the second stage of a Knot’s 14,000 km spring migration, from Delaware Bay to the Arctic.

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A short season

In Delaware Bay, horseshoe crabs spawn once a year, during the highest tides in May and early June, a period which overlaps with shorebird stopovers. The largest spawning events typically occur on a full-moon high tide, as long as the water temperature is higher than 15°C. Over the course of two decades, spring water temperatures have fluctuated in Delaware Bay; this annual variability in temperature is predicted to increase with climate change.

Prior to the paper by Anna Tucker and colleagues, which is at the heart of this blog, it had been shown that cooler temperatures cause delays in crab spawn, with consequences for migratory shorebirds. Anna’s research aimed to see whether Knot, which specialise on horseshoe crab eggs, are more susceptible to seasonal differences than Turnstone, which are more generalist foragers.

Knot and Turnstone both breed in the Arctic so they have similarly long journeys ahead of them when they leave Delaware Bay. The prediction was that individual Knot would show more variation in the timing and rate of mass gain than individual Turnstone and that mass gain in Knot, but not Turnstone, would be dependent on the timing of horseshoe crab spawning.

Catch, mark, weigh and re-sight

unnamed (1)Northward migration of Knot and Turnstone begins in late April/early May, with most birds arriving in Delaware Bay in mid to late May and staying for between one and two weeks, before continuing north to begin breeding in early June. The optimal breeding window in the Arctic is short and punctual arrival on territory is important if waders are to have a productive nesting season. This means that spring fattening at migration sites can directly affect breeding success. Weight data for both species were collected between 1 May and 5 June over a twenty-two-year period between 1997 and 2018, with horseshoe crab counts being made since 2003. Birds were marked with flags, with resightings in the same year providing an indication of length of stay. Recaptures of marked birds provided information on weight gain, while sightings in subsequent years gave estimates of apparent survival.

Key results from paper by Tucker et al

For both Knot and Turnstone, spring arrival was pretty consistent between years, over the 22-year period. Approximately 95% of individuals had generally arrived by the time of the seventh sampling period (26–28 May).

The proportion of horseshoe crab spawn that occurred by the time of peak shorebird arrival depended upon water temperature (see paper for details), ranging from just under a quarter (2003) to three-quarters (2004), with a median of 58%. Over the period of the study, there was no sign that the mismatch between horseshoe crab spawning and shorebird arrival was getting stronger.

unnamedMasses of most of the Knot and Turnstone caught in Delaware Bay were within the published range for the two species (Knot 125–205 g and Turnstone 84–190 g) with individually-marked Knot doubling their weight during their stay.

The estimated rate of mass gain per day varied between 2.7 g/day (2005) and 15.9 g/day (1997) for Knot and 2.2 g/day (2014) and 5.8 g/day (1998) for Turnstone. Between years, as predicted, there was far more variability in weight gain for Knot than for Turnstone, with the most pronounced difference being between the maximum rate of weight gain for individuals of the two species. The variability in this parameter for Knot was three times that for Turnstone. For both species, there were higher refuelling rates in years when mass gain started later in the season, with no trend in fattening rates, over the twenty-two-year study, for either species.

Not a lot of Knot

An earlier paper described the decline in Knot numbers in Delaware Bay and the probable link to the availability of horseshoe crab eggs. Rapid population decline in red knots: fitness consequences of decreased refuelling rates and late arrival in Delaware Bay. Allan J. Baker et al. Proceedings of the Royal Society B: Biological Sciences (2004)

  • From 1997 to 2002, an increasing proportion of knots failed to reach threshold departure masses of 180–200 g, possibly because of later arrival in the Bay and food shortage caused by over-harvesting of horseshoe crabs.
  • Resightings suggest that heavier birds in catches made between 1997 to 2002, were more likely to be seen again in subsequent years.

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This 2004 paper and subsequent annual counts of crabs and birds drew attention to overfishing problems in Delaware Bay, leading to a stakeholder-led adaptive horseshoe crab management plan, as described in this paper by McGowan et al. Developing the adaptive management plan required bringing together many groups of stakeholders, with very different values and objectives, to develop a strategy that would allow for the regulated harvest of horseshoe crabs, with a strong emphasis on protecting shorebird populations – especially Knot. The Delaware Bay horseshoe crab population now appears to be stable and it seems that shorebird populations using Delaware Bay have stabilized as well, although at much lower numbers than previously recorded in the Bay.

Conservation initiatives have restricted the impacts of the horseshoe crab fishing industry, reduced disturbance of feeding birds and showcased the importance of Delaware Bay to local people and visitors. You can learn more in this 15-minute programme: Feast on the beach http://www.delmnh.org/feast-on-the-beach/

tableAerial counts of Knot and other shorebirds have been taking place in Delaware Bay since 1981. Over this period Knot counts have varied but the big peaks of nearly 100,000 of the 1980s are now replaced by peaks that rarely exceed 25,000. See table taken from totals reported in USF&WS Rufa Red Knot background information and threats assessment. The declines in the Delaware spring passage numbers are similar in size to the drop in numbers seen wintering in Tierra del Fuego (far south of Argentina).

Why have Knot been so badly affected?

As outlined in the earlier papers and predicted at the start of the new study, the timing of pre-migratory fattening and the rate of mass gain were linked to timing of food abundance for specialist Knot but not for generalist Turnstone. Additionally, mass gain was far more variable in Knot, between years, suggesting greater sensitivity to local conditions (see figure). The way that Turnstones gain mass was more consistent across years and was not associated with abundance or availability of horseshoe crab spawn, which aligns with an ability to dig up buried eggs and switch to alternative prey items. The adaptability of Turnstone is discussed in the blog Why do Turnstone eat chips?

gain graph

The Knot is a highly adapted long-distant migrant. Studies elsewhere have shown that individual Knot can reduce the size of the gizzard, intestinal tract and organs, once they have fattened up for migration. Upon reaching Delaware Bay from southern South America, many Knot will have travelled over 6,000 miles.  The authors suggest that having an available supply of high‐quality soft‐shelled horseshoe crab eggs, which can be consumed without increasing gizzard size, may be particularly important to Delaware Bay Knot. Turnstone are thought more likely to migrate in shorter hops, a strategy that could be physiologically less challenging.

Knot refuelling was slower in years when there were more horseshoe crab eggs, suggesting that a slower mass gain is preferable and that there may be a physiological cost of rapid fat accumulation. Preliminary work (Tucker 2019) suggests that annual survival of Knot appears to be lower in years following springs in which individuals gain weight rapidly.

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In cooler years, with later horseshoe crab spawning, mass gain in Knot was faster, suggesting that birds try to “catch up” at the end of the season, to avoid a delayed departure. It would be interesting to know the upper limit of this extremely rapid mass gain, and whether there are costs to piling on the fat. Such costs could be physiological, in terms of flight efficiency, or there could be increased predation risk if vigilance is compromised while feeding more intensively, for instance.

Breeding shorebirds are constrained by a narrow time window for nesting and a fixed single‐clutch size (usually four eggs). This means that they have little flexibility to compensate for unfavourable conditions previously encountered during migration. In a warming world, with more unpredictable weather patterns, mismatches between food supply and the timing of migratory fattening could well occur more frequently, with downstream consequences for productivity and annual survival rates. The authors point out that this could be particularly bad news for populations of shorebirds that have limited capacity to vary timings within their annual cycles.

In conclusion

unnamed (3)Long‐distance migrants rely on predictable resources at stopover sites; even when these linkages are simple and predictable, populations can be vulnerable to change. The Tucker paper suggests that generalist foraging strategies, as used by Turnstone, may dampen the negative effects of phenological mismatch.

The Knot that use Delaware Bay have probably been relying upon horseshoe crab eggs for centuries and, as long as conditions remain predictable, this remains a good strategy. Over the years, there will have been cold springs, with consequent lower productivity and reduced survival, and other springs in which a superabundance of eggs has fuelled a wonderful summer of eggs, chicks and high survival. Overfishing of horseshoe crabs and more unpredictable spawning conditions appear to have tipped the balance and may (at least in part) explain huge declines in the number of Knot that visit Delaware Bay in spring. This population of Knot has been paying the price for being fussy eaters.

Details of paper

Foraging ecology mediates response to ecological mismatch during migratory stopover. Anna M Tucker, Conor P McGowan, Matthew Catalano, Audrey DeRose-Wilson, Robert A Robinson & Jordan Zimmerman. Ecosphere.

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GFA in IcelandGraham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland. He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

 

Travel advice for Sanderling?

blog 9 wint plum ringedHave you ever seen a colour-ringed Sanderling and perhaps wondered why it spends the non-breeding* season on a British or Irish beach rather than on one in Portugal, Ghana or even further south? Why fly from Greenland to Namibia, a distance of over 20,000 km, when spending the winter months in the UK or Ireland requires a flight of as little as 3,700 km? Perhaps the chance of survival is greater in other countries or perhaps birds that travel further have a larger lifetime breeding output? A paper by Jeroen Reneerkens and colleagues provides some of the answers.

*The term non-breeding season (rather than winter season) is used in this blog because Sanderling travelling as far as Namibia experience a southern summer at the same time as UK birds are experiencing a northern winter.

Pros and cons of travelling further?

At the end of the summer, juvenile Sanderling from Greenland start heading south. The first migration might take an individual to Scotland or Namibia, in southern Africa – or anywhere in-between. The circumstances that lead to these initial settlement patterns are unknown but an individual will repeat its first migratory journey every year, with some birds travelling just 7,400 km annually and others travelling over 44,000 km. It has been argued that, for a range of migration strategies to persist, different wintering sites will have balancing pros and cons. This suggests that costs of longer migrations might be matched by benefits gained at the non-breeding destinations. Is this really true?

blog 5 juv Hebrides

Just six weeks after being ringed as a chick, this Sanderling was photographed in Mull (island off the west coast of mainland Scotland)

Using data provided by colour-ring sightings, Jeroen Reneerkens and colleagues assessed three factors that might affect the fitness of individual birds that spend the non-breeding period in different areas.

  • Annual adult survival: If a bird from one non-breeding location is more likely to survive than a bird that spends the non-breeding season somewhere else, it should live longer and potentially have more breeding attempts within a lifetime.
  • Age when a bird makes its first migration northwards: A young individual that flies north in its first spring will potentially have one more breeding opportunity than a bird that remains in the non-breeding area for its first summer.
  • Timing of migration: There is a short breeding window in the High Arctic so a bird that migrates north earlier in the spring may have higher reproductive success, because it will have a higher chance to re-nest if a first clutch is lost. (There is more about this in Time to nest again?)

Studying marked birds

map no arrowsSanderling were captured and ringed in breeding sites in northeast Greenland, at staging areas during migration (SW Iceland, N Scotland and the Dutch Wadden Sea) and in the non-breeding season (Scotland, England, Portugal, Mauritania, Ghana and Namibia). The different analyses in these studies used data from 5,863 Sanderling, of which 5,220 were individually colour-ringed.

Survival rates. By visiting key sites and collating additional reports of ringed birds from hundreds of birdwatchers, the research team were able to estimate the annual survival rates of Sanderling that spent the non-breeding season in England, France, Portugal, Mauritania, Ghana and Namibia. As can be seen in the table, the apparent survival rate in West Africa (Mauritania and Ghana) was much lower than that in Europe or Namibia. A bird with an annual survival rate of 0.75 is 67% more likely to die in any given year than a bird with a survival rate of 0.85. Confidence limits and methodological notes are provided in the paper. There is a WaderTales blog about the importance of measuring survival rates.

sa plus table

Age of first northward migration. The proportion of colour-ringed juveniles that migrated north in the first spring varied significantly, with virtually all Portuguese and English juveniles migrating north but only 35.8 % of those from Ghana and 9.6 % of those from Mauritania. (There were insufficient data to work out figures for Scotland, France and Namibia).

Timing of northward migration. Observations in Iceland provided information on the timing of migration of Sanderling from a range of non-breeding locations. This is the last possible stop-over site on northward migration, before birds migrate to their Arctic breeding sites in Greenland or Ellesmere Island in Canada. Birds from Ghana were observed in Iceland between 5 and 9 days later and those from Mauritania between 10 to 13 days later than the birds from Europe or Namibia. That is a considerable difference, given the short breeding period.

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Flock of summer plumage Sanderling, on migration in Iceland

Summary

The authors asked the question “is there equal fitness throughout the non-breeding range?”, as inferred from the three measured discussed above. The answer seems to be “no”. Sanderling from non-breeding areas in West Africa had lower annual adult survival, delayed first northward migration and later passage through Iceland than birds wintering either further north or south.

map cross Africa

Sanderling travelling north from Namibia do so by crossing the Sahara (generalised route – sample tracks are shown in paper)

Using geolocators**, the team was able to show that birds from Namibia bypassed potential staging sites in West Africa on the way north, flying north across the African continent to Europe, with some birds stopping briefly in the central part of the Mediterranean before spending a longer stop-over in NW Europe, thereby overtaking the Sanderling from West Africa. Namibian individuals used both Mauritania and Ghana as staging areas during southward migration.

** The use of geolocators is discussed in this blog.

The West African sites seem to be relatively poor places in which to spend the non-breeding months of the year. Food availability in spring is likely to be the chief problem. Theunis Piersma and colleagues have shown that the quality and biomass of prey available to shorebirds is lowest close to the equator, resulting in low fuelling rates and low body masses at departure for northward migration in Knot (Piersma et al. 2005).

Sanderling occupy a variety of different and widely-dispersed non-breeding sites between the northern tip of Scotland and the southern tip of the African continent. Here, they experience very different conditions which affect potential, life-time breeding outputs. Sites which appear to be poorer continue to be used, even though there are better options elsewhere, simply because individual birds have no knowledge of other potential areas where they could spend the non-breeding months.

A roll of the dice?

Once a juvenile Sanderling has settled upon a particular migration strategy and a spot in which to spend the non-breeding season, he or she will continue on the same annual cycle for the rest of his/her life. One of the big unknowns for waders/shorebirds – and for other groups of migrant birds for that matter – is just how these settlement patterns develop. (See Generational Change to read how young birds can create new patterns of migration).

Checking their data, Jeroen and his colleagues could see no pattern in the juvenile/adult proportions, sex ratios or sizes of the birds in different non-breeding areas that would help to explain differences in fitness. Birds from the same breeding areas of Greenland end up in non-breeding locations along the whole north-south range. It is almost as if the dice are rolled and a juvenile ends up where chance events take it.

blog 2 flying

At the level of the individual:

  • A Sanderling that spends the non-breeding season in Ghana does not know that it would have a better annual survival rate and be likely to return earlier to Greenland each spring had it ended up wintering in England or travelled as far as Namibia.
  • A bird in Namibia has no idea that it could have saved itself an accumulated migration distance of 37,000 km each year by stopping in England, without affecting its probability of survival.
  • A first-year bird that spends its first potential breeding season feeding on the beaches of Mauritania, will be unaware that first-years from Portugal have all travelled north to Greenland.

blog 8 look for crIt’s amazing what colour-ring readers have helped to discover but there is much still to learn about the migration strategies of individual waders.

Let’s hope that birdwatchers will continue to look out for colour-rings, as flocks of Sanderling chase the waves in and out on beaches throughout the world.

 

Paper in Journal of Animal Ecology

Low fitness at low latitudes: wintering in the tropics increases migratory delays and mortality rates in an arctic- breeding shorebird

Jeroen Reneerkens, Tom S. L. Versluijs, Theunis Piersma, José A. Alves, Mark Boorman, Colin Corse, Olivier Gilg, Gunnar Thor Hallgrimsson, Johannes Lang, Bob Loos, Yaa  Ntiamoa-Baidu, Alfred A. Nuoh, Peter M. Potts, Job ten Horn & Tamar Lok.

blog 6 run for it


GFA in Iceland

Graham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

Sixty years of Wash waders

wwrg tt balance

Weighing a Turnstone

The Wash Wader Ringing Group (WWRG) started with a bang on 18 August 1959, when the team made a catch of 1,132 birds in a Wildfowl Trust rocket-net at Terrington, in Norfolk. Over the years, cannon have replaced rockets, catches have become generally smaller and the scientific priorities have been refined, but the Group continues to focus upon discovering more about the waders that use the Wash. This blog attempts to summarises what has been learnt about the waders that rely upon the Wash, the vast muddy estuary that lies between Lincolnshire and Norfolk, on the east coast of England.

Sixty years ago, the first goal was to understand where the vast flocks of waders that visit the Wash came from – a task that would provide great insights into the way that the whole East Atlantic Flyway works. In this time, over 300,000 birds have been caught and ringed on the Wash, as you can see in the table below. Equally importantly, hundreds of bird-ringers from across the UK and scores of visitors from around the world have joined WWRG teams, in order to learn more about the study of shorebirds. Further international collaboration has been fostered through overseas visits by WWRG members and emigration of some key personnel. The impact of the Group is truly global, as you can read in the WWRG report for 2014/2015.

wwrg table

A total of 307,226 birds is impressive, especially when some of the species totals are compared to the national totals of the BTO Ringing Scheme for the whole of Britain & Ireland since 1909. WWRG is responsible for over 40% of the Grey Plover, Knot, Sanderling and Bar-tailed Godwit, with Grey Plover topping the list at nearly 60%. These are terrific achievements for a group of volunteers. I don’t have the figures but I reckon that Nigel Clark has been responsible for the largest number of catches.

Wee quiz: What’s the best match between these Wash waders and the countries that they are quite likely to have come from? Answers at the end of the blog:

  • Species: Bar-tailed Godwit, Black-tailed Godwit, Curlew, Oystercatcher, Sanderling, Turnstone
  • Countries: Canada, Greenland, Iceland, Norway, Finland & Russia
wwrg box

Firing box connected to 4 cannon-nets

In the early days, rocket nets were borrowed from the Wildfowl Trust for an annual summer week of catches, but the development of cannon-nets gave opportunities for all-year ringing. The intensity of the Group’s activities grew in the 1970s, when there was a threat to build a freshwater reservoir on the mudflats. For a couple of years, Clive Minton (founder and leader) persuaded us to visit fortnightly, so that we could get better data on weight-gain and turn-over, using a mixture of cannon-netting and mist-netting. Everything we knew was published by the Group as The Wash Feasibility Study in 1975. These days, the Group gets together about ten times a year for catching and colour-ring-reading sessions.

wwrg oldies

By catching and ringing large numbers of the key species that visit the Wash, the Group was able to generate maps showing what are now well-known patterns of migration (see Which wader, when and why?). Early on in the Group’s history, there was a focus on nine species, with Black-tailed Godwit added as a tenth when numbers increased. Each of these species has its own section below. The maps were prepared for the Wash Wader Ringing Group 2016/2017 Report by Ryan Burrell, using data stored within the BTO archives. Blue dots represent WWRG-ringed birds that have been found abroad. Red triangles represent foreign-ringed birds caught on the Wash. The base maps used are by courtesy of Natural Earth (www.naturalearthdata.com).

Oystercatcher

wwrg map OCThe map alongside clearly demonstrates the strong link between the Wash and Norway. Other interesting things that have been discovered about Oystercatchers:

  • They live a long time. An Oystercatcher that we caught at Friskney on 30 July 1976 broke the longevity record for a BTO-ringed wader when it was shot in France on 4 April 2017 (41 years 1 month and 5 days). It was ringed as an adult so we don’t know the exact age – but it must have been at least 43 years old. There’s a WaderTales blog with a list of longevity records for BTO-ringed waders.
  • When life gets tough, Oystercatchers fail to complete their autumn moult, retaining some of their outer primaries for an extra year. The ability to complete moult and annual survival rates are both affected by cockle and mussel supplies on the Wash. There’s more about this in two papers in Biological Conservation and the Journal of Applied Ecology.

Grey Plover

wwrg GV GVIn the early days of the WWRG, Grey Plovers occurred in much smaller numbers than they do now. Writing in an article about the first 40 years of the Group, Clive Minton told the story of the first catch of 100, made in 1963, that was celebrated with three bottles of champagne provided by the late Hugh Boyd, delivering on an incentive that he had promised.

  • Over half of the Grey Plover that have been ringed in Britain & Ireland since 1909 have been ringed by WWRG since 1959 (58.9%)
  • All of the Grey Plover using the Wash breed in Siberia. Some birds spend the winter on the Wash but there are autumn moulting flocks of birds that will go on to winter in other parts of Britain & Ireland, and spring and autumn passage of birds that travel as far south as West Africa.
  • Grey Plover are late to leave the Wash, with the last departures not occurring until the start of June. Unsurprisingly, they are some of the last waders to return at the end of summer, which puts pressure on birds to finish moult before the short, cold days of winter. Some adults fail to complete primary moult, especially if food supplies are low. There is more about Grey Plover moult in this WaderTales blog.

wwrg map GV KN

Knot

wash knot

First-winter Knot (subterminal bands on wing coverts and, as yet, unmoulted juvenile fethers on upper-parts)

Knot (or Red Knot) are truly international waders, as is shown in this map of movements of islandica  (and a few canutus) birds  to and from the Wash. Several WWRG members have been heavily involved in efforts to understand the decline in numbers of the rufa subspecies in Delaware Bay (on the North American eastern seaboard) and Clive Minton has been at the heart of efforts to explain the sudden drop in survival of piersmai and rogersi adults that winter in Australia and migrate to Arctic Russia via the Yellow Sea (see Wader declines in the shrinking Yellow Sea).

  • We are still learning about Knot migration. The cluster of reports of WWRG-ringed birds in Northern Norway looks odd on this map projection but it turns out that this is a well-used stopping-off point for islandica Knot heading for northern Greenland and NE Canada. This route was first confirmed in 1985, when a joint Durham University and Tromsø University expedition caught 18 Wash-ringed birds in a total catch of 1703 birds.
  • The dot in Siberia looks odd but isn’t. This will be a bird of the canutus race, small numbers of which pause on the Wash in autumn and spring, on their way between the Russian Arctic and west Africa.
  • wwrg net set

    Setting cannon-nets

    Many birdwatchers visit the Wash in autumn and winter to see the swirling Knot flocks at Snettisham and Holme. If high tide is at first light, Knot and other waders sometimes roost on Heacham Beach, giving the occasional opportunity to make a significant catch. The most recent of these, on 11 February in 2012, included 2757 Knot, 77 of which were already wearing rings.

  • The most recent analysis of wader populations in Great Britain showed that there was a drop of nearly 20% in wintering Knot numbers (from 320k to 260k) in less than a decade (see Do population estimates matter?). Regular catches on the Wash will help produce estimates of annual survival rates and age ratios of the islandica subspecies.

Sanderling

wwrg sanderlingThe biggest catches of Sanderling are generally in the summer, when the Wash is a meeting point for birds from Greenland and Siberia. July can sometimes see catches of 200 or more birds. Traditionally, a Sanderling catch was the curtain-raiser at the start of Wash Week, an opportunity for the whole team to make one catch before splitting into ‘Terrington’ and ‘Lincolnshire’ teams for the rest of the main summer trip.

  • Wintering Sanderling on the Wash are thought to be exclusively of the race that heads northwest in the spring, to Greenland via Iceland.
  • Late summer and spring see the addition of birds passing through on their way from/to Siberian and Greenlandic breeding areas.
  • I well remember the first time we caught a Sanderling (on 26 July 1975) wearing an Italian ring (caught in Italy 9 May 1975). Thanks to Jeroen Reneerkens (whose work will be covered in an upcoming blog) I now understand that this is probably a bird that migrates from Namibia to Greenland in spring, via the Mediterranean. It will have been on its way back to Namibia when caught in July.

wwrg map SS DN

Dunlin

wash dunlin

Sam Franks, looking for the buffy tips on inner coverts, which distinguish first-year birds from adults

Nearly half of the waders caught by WWRG have been Dunlin – a total of 140,168 up until the end of 2018. There were really big flocks of Dunlin in the 1970s but numbers have dropped over the years, with peak counts now half what they were, according to WeBS data.

  • We caught over 3,500 Dunlin in one week in 1976 but the annual total has exceeded 1,000 in only four of the last ten years. Partly, this reflects a change in behaviour in the summertime, with fewer waders roosting on fields and hence less catchable.
  • Three races of Dunlin visit the UK. Our winter birds are alpina, from Siberia, NW Russia and northern Scandinavia. A lot of July birds are schinzii, breeding in the UK and as far north as Greenland, and we occasionally try to convince ourselves that we have caught an arctica from northern Greenland.
  • Data collected for the WeBS survey suggest that national winter totals have dropped by over 40% in 25 years. This could perhaps partly be explained by a redistribution of alpina, with new generations of young birds settling in wintering areas on the other side of the North Sea. Warmer winters may well make this a more practical proposition than in the 1970s. There’s more about this in this paper.

Black-tailed Godwit

wash blackwit

Newly ringed Black-tailed Godwit, caught in a mist-net at night.

Black-tailed Godwits became a priority species in 1995, when Jennifer Gill (University of East Anglia) started a project to study the movements of individuals, using colour-rings. Nearly 25 years later, the WWRG-ringed Black-tailed Godwits have contributed data to numerous papers, largely focusing upon migration.

  • The Wash is a hugely important area for moulting islandica Black-tailed Godwits. Some birds stay in East Anglia for the winter but others move south and west within the UK, west to Ireland and south to France, Portugal and Spain.
  • There are several blogs about Black-tailed Godwits in this WaderTales contents list.

Bar-tailed Godwit

One of the key things that was learned from the sudden decline in annual survival rates in a range of species that use the Yellow Sea (as mentioned above) is a need for regular monitoring of marked birds. The WWRG’s Scientific Committee set up colour-flagging projects for Bar-tailed Godwit, Curlew and Grey Plover, in order to increase the reliability of estimates of annual survival for three species that the Group does not catch in sufficient numbers to generate good retrap histories. Birdwatchers can help by reporting colour-marked birds here.

wwrg barwit map etc

  • In Bar-tailed Godwits: Migration & Survival there is a comparison of the data generated by a catch of 505 Bar-tailed Godwits in 1976 with the information that has been generated recently, using colour-flags.
  • Bar-tailed Godwits are long-lived birds. A WWRG bird holds the current record for a BTO-ringed Bar-tailed Godwit: 33 years and 11 months between ringing in 1978 and recapture in 2008. BTO longevity records are discussed in this WaderTales blog.
  • Colour-ring reading is now a significant element of Group activities, as described by Rob Pell in the WWRG Report for 2016/2017.

Curlew

Back in the 1970s, Curlew were still hunted on the Wash (paté made from autumn-shot birds was reported to be very tasty). Shooting stopped in Great Britain in 1981, when the maximum winter count on the Wash had dropped to about 3,000 birds, and by 2003/04 the maximum winter count was 15,336. Since then, numbers have declined, in line with national and international trends.

wwrg curlew map etc

  • A large number of Curlew on the Wash in winter are from Finland and surrounding countries. Surprisingly few are of UK origin.
  • Birds wearing WWRG leg-flags have been observed breeding in the Brecks (Norfolk/Suffolk).
  • The Curlew is internationally designated as ‘Near Threatened’. Is this really true when we can still see a field with 1000 roosting Curlew in Norfolk? Answers here.

Redshank

wash redshThe latest population estimates suggest that Great Britain has lost 26,000 wintering Redshank in less than a decade, representing a drop of 20%. Perhaps WWRG data can be used to help to explain these declines? Here are some of the things we know:

  • The Redshank on The Wash in the winter are mainly a mixture of birds from around the Wash, across the UK and from Iceland.
  • In cold winters, Redshank wintering on the Wash die in large numbers. After a period of severe weather in 1991, nearly 3,000 wader corpses were collected from along the tide-line, about 50% of which were Redshank. The winter WeBS counts for Redshank dropped by 50% after this mortality event but have recovered somewhat since then.
  • An analysis of nearly 1,000 dead Redshank showed that about two-thirds were of Icelandic origin. There was a tendency for smaller birds to be more susceptible to cold weather mortality than larger birds of the same species (More information in this paper by Jacquie Clark)

wwrg map RK TT

Turnstone

wash ttWinter Turnstone are birds that will head for Greenland and NE Canada in the spring but recoveries of birds in Finland and other Scandinavian countries indicate a passage of continental birds. African recoveries of WWRG-ringed birds probably include birds from Canada/Greenland and Finland/Scandinavia.

  • Turnstone wearing US Fish & Wildlife Service rings are occasionally caught on the Wash. Some of these rings were put on by Guy Morrison and his colleagues in Alert, Ellesmere Island, Canada. Guy was an early member of WWRG. It’s a small world!
  • The first Wash Turnstone were colour-ringed in 1999, as part of a study to understand why birds were feeding on the docks at Sutton Bridge. There is a WaderTales blog about the resulting paper by Jen Smart and Jennifer Gill. Colour-ringing continues, to measure annual survival rates.
  • Turnstone have a reputation for eating almost anything (including dog excrement and a human corpse) so do not be surprised if you see a colour-ringed bird scavenging for chips on the Hunstanton sea-front.

A few more highlights

Ringed Plover: this is not one of the ten key study species but 1,432 have been ringed between 1959 and 2018. Some birds are local breeders that hardly move anywhere but other birds link the Wash with Greenland, northern Norway, Morocco and Senegal.

wwrg GKGreenshank: The Group supports a colour-ringing project that was initiated by Pete Potts, in Hampshire. More information here.

Spotted Redshank: During the period 1959 to 2018, WWRG ringed a total of 85 Spotted Redshank, representing over 20% of the total ringed in Britain and Ireland since 1909. Amazingly, sixty of these birds were ringed on the same day – 27 July 1975. There is a blog about this catch and the recent decline in the number of Spotted Redshank visiting the UK. Fewer Spotted Redshanks.

Ruff: Until its closure, WWRG members spent many a smelly night at Wisbech Sewage Farm. This was a great place to catch Ruff, Curlew Sandpipers, Green Sandpipers etc. in mist-nets. Group members wrote a paper about Ruff moult and migration.

Rares: Occasionally there are surprises! WWRG has caught one each of Stone Curlew, Pectoral Sandpiper, Broad-billed Sandpiper and Terek Sandpiper. The last bird features in this WWRG blog.

What do we know now?

Migration studies have revealed the importance of the Wash to half a million or more waders each year – birds that spend the whole winter, others that refuel in the spring and vast numbers that rely on the food supplies in the mud to provide the energy for the post-breeding moult. There’s a selection of papers that have included WWRG data here, on the Group’s web-site.

wwrg cr TTThe Group still aims to maintain its general ringing programme, so that a representative sample of the key species carry rings. Colour-ringing projects aim to provide survival estimates for Curlew, Bar-tailed Godwit, Grey Plover and Turnstone, with Greenshank and Black-tailed Godwit colour-rings contributing to migration studies. Birdwatchers who visit the Wash can help by reporting colour-marked birds here, on the WWRG web-site.

WWRG data have been used to help inform decisions about the future of the Wash but the threats keep coming. Studies of migration and seasonal turn-over in numbers contributed hugely to decisions to provide national and international protection to the area and to fend off the 1970s plan to build a freshwater reservoir on the rich mudflats. The information that has been generated by many generations of volunteers over a period of sixty years has been used to manage the level of shellfish exploitation, to inform decisions about wind turbine locations and to manage activities that can cause disturbance.

The Wash Wader Ringing Group is very keen for its data to be used – and not just for impact assessment studies. Click here to learn more.

Diamond Jubilee

PLI

Phil Ireland releasing a Curlew

Over one thousand people are estimated to have contributed to sixty years of the Wash Wader Ringing Group’s activities. We have lived in barns, rolled cars, dug tens of thousands of holes, carried nets for miles, made important catches, had depressing failures, got frostbite, been threatened by surge tides and made friends for life.

In the whole of this period, there have been only two leaders of the Group – Clive Minton* (1959-1981) and Phil Ireland (1981-present). Bird ringers, wader biologists and millions of waders owe them both a huge debt of gratitude.

You can read more about the history of WWRG on the Group’s website:

*Clive Minton died in a car crash a few months after this blog was written. Friends and colleagues have shared some wonderful memories on the IWSG website.

wwrg sunset

Photo at the top of this blog is by Cathy Ryden. Many thanks to her and to other photographers.

Wee quiz:

  • Bar-tailed Godwit – Russia
  • Black-tailed Godwit – Iceland
  • Curlew – Finland
  • Oystercatcher – Norway
  • Sanderling – Greenland
  • Turnstone – Canada

 


GFA in Iceland

Graham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

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Generational change

blog TGG on postIn a changing world, with more chaotic weather patterns and rapidly altering habitats, migratory birds are faced with opportunities and challenges. Long-term monitoring of colour-ringed Black-tailed Godwits, during a period of range expansion and phenological change, has revealed that individuals behave consistently over time but that the behaviour of new generations is moulded by the conditions they encounter.

A changing world 

When trying to explain observed changes in the distributions and annual cycles of migratory birds, there are many things to consider:

  • blog VM y flag

    Colour-rings enable life-time tracking. This bird, caught on its nest, had been ringed as a chick.

    Are individual birds able to take advantage of new breeding and non-breeding sites, as they become available, particularly if other areas become less suitable?

  • Are individuals able to change the timings and patterns of migration?
  • Do individuals adjust their migration routes as a consequence of changes in stop-over or wintering areas?
  • If individuals do not change what they do, how do we explain range expansions and changes in timing of migration?

Put simply, how does climate change lead to changes in distribution of migratory birds? Answering this question is key to being able to predict the rate and direction of future changes, and to assess whether our existing networks of protected sites will continue to support populations in the way that was intended. This issue was tackled by Jennifer Gill, José Alves and Tómas Gunnarsson in their paper “Mechanisms driving phenological and range change in migratory species”, published in Linking behaviour to dynamics of population and communities: applications of novel approaches in behavioural ecology and conservation, a special issue of Philosophical Transactions B (Royal Society).

Potential models

Change could happen in two main ways:

  • Individuals could relocate – having knowledge of a range of available conditions, they can choose to move elsewhere.
  • New generations could settle in new areas (in the breeding season, the non-breeding season or both) and/or adopt new migratory strategies.
blog map

Map that illustrates range expansion

Working out whether change happens through individual movement or generational shifts can only be done by life-long tracking of individuals, in populations in which range change is happening. The Icelandic population of Black-tailed Godwit is ideal for such an investigation. Black-tailed Godwits have been expanding into new breeding areas of Iceland for over 100 years, as discussed in this WaderTales blog. Population growth has been facilitated through warming spring conditions, as discussed in From local warming to range expansion.

blog TGG juvs

Naive youngsters, gathering together before migration

Icelandic Black-tailed Godwits fly south in the autumn, to spend the winter in the British Isles, The Netherlands, Belgium, France, Spain and Portugal. As numbers have grown, winter counts have increased in many areas, with new flocks appearing and expanding on estuaries and areas of wet grassland where the species was previously absent or scarce.

 

Winter distribution

The Wetland Bird Survey shows that there are three times as many Black-tailed Godwits wintering in Great Britain as there were 25 years ago. The biggest changes in numbers have occurred on estuaries in the northwest of England, with the Morecambe Bay winter maximum rising from about 180 to 3200, for instance. Where have these extra birds come from?

blog juvs on Axe

These young birds happen to have ended up on the Axe Estuary in Somerset

Black-tailed Godwits have been ringed in Iceland for nearly twenty years, providing a pool of known-age adults for which natal sites are known. Winter observations of colour-ringed individuals have shown an interesting pattern; birds breeding in newly-colonised areas, particularly in north and east Iceland, are the ones that are more likely to be found in newer winter sites.

In their paper, the authors suggest that birds nesting in these colder areas, where spring comes later, will be fledging quite late and leaving Iceland after adults have departed. With no experienced birds to follow, these young birds may well stop off at the first suitable site, many of which are in the north of the wintering range, and then they return to breed in their natal sites. Birds in Morecambe Bay don’t know that days are longer and the weather is kinder for other birds that travel further south to wintering areas such as Portugal.

blog RS Dee

Wintering birds in Northwest England

Observations from birdwatchers show that the same colour-ringed individuals are nearly always found at the same wintering sites each year. Whatever mechanism is producing this new-breeding-site to new-wintering-site link, it is becoming clear that older birds continue to do what they have always done, with changes in distribution happening as a result of a generational shift.

The annual cycle

Colour-ringed Black-tailed Godwits have been tracked for over 25 years, with a small number of individuals contributing data for the whole of this period. This tracking information can be used to ask how much individuals move around and experience different sites and to assess whether individuals from different generations are using different parts of the range.

Using colour-rings, the Black-tailed Godwit team has discovered that, although individuals can live for over 20 years, in that time they generally use a total of only about four sites between leaving Iceland in late summer and returning in the spring. Basically, individual birds have very limited experience of sites and there is no evidence that they have moved to occupy different sites as, for instance, winter conditions have changed.

blog infographic

Spring arrivals in Iceland

Colour-ring observations have shown that individual birds do not change their breeding or wintering locations and that migrating individuals often appear in the same stop-over sites year after year. The timing of movements is also pretty consistent, especially in the spring. A previous WaderTales blog called Why is spring migration getting earlier? demonstrated that the timing of  migration of individual Black-tailed Godwits varies very little, with observed shifts in the period of migration being driven by young birds returning to Iceland for the first time on average doing so somewhat earlier than previous generations. Once individual birds settle into a timing pattern, they stick to it.

blog LJ arrivals

Black-tailed Godwits, newly arrived in Iceland after crossing the Atlantic

Migration patterns

As discussed above, individual Icelandic Black-tailed Godwits have experience of only a small number of sites, which they use on an annual cycle. When migrating, a bird will generally use the same stop-over site when breaking its journey south, to undertake autumn moult, or on their way north, to take on fat for the trans-Atlantic journey. There is a range of spring migratory strategies in islandica Black-tailed Godwits, as discussed in Overtaking on migration.

blog wwrwOnce established, the annual migratory programmes of individuals rarely change, as illustrated by the map to the right. Colour-ringed Black-tailed Godwit W-WR/W regularly moulted on the Wash, in eastern England, before spending the late winter and spring in northwest England. In the late summer of 2002 he was reported at Slimbridge on 18th and 20th July but back on the Wash on the 25th. Having made the Atlantic crossing and ended up in southwest England, he was able to correct what he may have perceived to be his mistake, returning to the moulting area that he had been using since at least 1996.

Individuals might not change their annual migration routes but we do see changes in numbers on different sites that are used during migratory stop-overs. In a paper published in 2018, Mo Verhoeven and colleagues investigated whether observed changes in migratory patterns of a population of the limosa subspecies of Black-tailed Godwit were caused by individuals altering their strategies or by generational change.

Limosa Black-tailed Godwits leave breeding areas in countries such as The Netherlands in late summer, heading south to either West Africa or Iberia, where they spend the winter. In spring they all gather in staging sites in Portugal and Spain, typically on rice fields. Over the course of less than ten years, the average peak number in Extremadura (Spain) has dropped from about 24,000 to 10,000, while the numbers on the Tagus and Sado estuaries rose from 44,000 to 51,000. These changes took place during a period of rapid population decline, as described in this blog focusing on a paper by Rosemarie Kentie and colleagues.

blog VM Tagus

Limosa Black-tailed Godwits feeding in a rice field in the Tagus estuary

Mo Verhoeven et al have shown that this rapid population-level shift in spring stop-over sites from Spain to Portugal, 300 km further west, was driven by young godwits increasingly using Portugal in the period January to March, instead of Spain. Nearly all of the older birds stuck with the routes they knew. The paper is Generational shift in spring staging site use by a long-distance migratory bird.

Change happens to birds

One thing that is becoming clear in Black-tailed Godwits is that birds are being affected by change – individuals do not have the knowledge or flexibility to effect change. Even in long-lived birds, like Black-tailed Godwits, we see no evidence of individuals altering what they do over what is now two decades, despite the fact that the species’ migration dates, wintering areas and migration routes have all perceptibly changed over the same time period. It’s all about generational change. The behaviour patterns of young birds arise from the conditions they encounter in the first year of life, after which they are repeated.

Details of the Generational Change paper by Gill et al

blog LJ sum plumThe paper at the heart of this blog is: Mechanisms driving phenological and range change in migratory species by Jennifer Gill, José Alves and Tómas Gunnarsson, from the Universities of East Anglia (UK), Aveiro (Portugal) and Iceland. It is published in Linking behaviour to dynamics of population and communities: applications of novel approaches in behavioural ecology and conservation, a special issue of Philosophical Transactions B (Royal Society).

The paper could not have been produced without the help of “thousands of observers of colour-ringed godwits who have made these analyses possible”. This WaderTales blog is a celebration of the work they do: Godwits and Godwiteers.


GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.

@grahamfappleton

 

Whimbrel: time to leave

blog WW-WLGeolocators* have provided fantastic information about the movements of migratory birds – making links between countries, revealing previously unknown stop-over sites and indicating just how quickly birds traverse our planet. A small number of Icelandic Whimbrel have carried geolocators for up to six annual cycles, providing Camilo Carneiro with an opportunity to investigate the annual consistency of egg-laying, autumn departure, arrival in West Africa, departure in the spring, stopover in Western Europe and arrival back in Iceland.

* Geolocators are tiny devices that record the daily positions of birds, by measuring the timing of dawn and dusk. An individual typically carries a geolocator for a year and then needs to be re-caught for the data to be downloaded.

Planning a trip

When booking a train journey on-line, the first question I am asked is whether I want to stipulate departure time or arrival time.  In early spring, with breeding on their minds, you might think that Whimbrel will focus on the time they need to be in Iceland, rather than the time they leave West Africa? If that’s the case then it might be best to take early spring opportunities if they arise, to catch express winds that will make the journey as rapid as possible and to get to Iceland early. Is that the case?

blog mangroves and beach

The Whimbrel is one of several wader species that breed in Iceland. Each autumn, Redshank, Snipe, Golden Plover, Oystercatcher and Black-tailed Godwit fly south to Europe, especially Ireland and the United Kingdom, but many Ringed Plover, most Dunlin and most Whimbrel travel as far as Africa. The main wintering sites for Whimbrel are in West Africa, south of the Sahara, in countries such as Guinea-Bissau. Here they can be seen feeding on crabs on the mangrove-fringed muddy shoreline (above). It’s a very different environment to the inland floodplains of Iceland (below).

blog river plain

In a paper by Tómas Gunnarsson & Gunnar Tómasson in 2011, we learnt that Whimbrel arrival times in Iceland did not change much between 1988 and 2009 (just 0.16 days earlier per year), while timing of arrival was advancing much more in species that travel less far to winter grounds, as you can see in this diagram.

wader arrival Tand G

Changes in first spring arrival dates of six species of waders in southern Iceland from 1988 to 2009 (reproduced from Gunnarsson & Tómasson 2011).

The arrival date for Black-tailed Godwit was advancing fastest (0.81 days per year). In more recent research, it has been shown that the rapidly advancing trend for Black-tailed Godwits is being driven by new recruits to the population – individual adults are not changing their schedules. Why is spring migration getting earlier? summarises a paper by Gill et al in Proceedings of the Royal Society B.

The Whimbrel trend has been recalculated, with a longer run of years, and the new change of 0.03 days earlier per year is not significantly different from zero. Given that Whimbrel are breeding alongside other species that are arriving in Iceland much earlier than thirty years ago, what are the constraints to the timing of their migrations?

Migration timings for Whimbrel

Camilo Carneiro, José Alves and Tómas Gunnarsson from the Universities of Aveiro (Portugal) and Iceland have been studying a population of Whimbrel in Southern Iceland. Birds are caught on the nest in one year and then re-caught in the subsequent year – or two years later if a bird evades capture in the intervening summer. The following results summarise weeks and weeks of patient fieldwork and brush over the hours of frustration caused by wary birds that have been caught before!

blog catching

Over the course of the whole study, 86 Whimbrel were fitted with geolocators, 62 of which were retrieved. Repeatability could be calculated for 16 birds, with between 2 and 7 years of data collected from each individual. The results are summarised in these few bullet points. Please see the paper for confidence intervals and more details about differences between the sexes.

  • Blog tagIndividual timings of autumn departure from Iceland varied between years. The repeatability index is 0.28, with a suggestion of a gender difference (females 0.40, males 0.02). Males tend to look after chicks for a longer period than females so their departure dates may be more strongly influenced by the success of each year’s breeding attempt.
  • Autumn arrival time in West Africa was closely linked to departure time because, on all but one occasion, southward migration was achieved through a single direct flight. See Iceland to Africa non-stop.
  • Spring departure time from West Africa was highly consistent, with a repeatability index of 0.76 and no discernible difference in repeatability between males and females.
  • blog long green grassSpring arrivals in Iceland. Some Whimbrel that managed to complete spring migration in a single flight in some years stopped off in other years. These breaks, perhaps to wait for more helpful wind conditions and/or to refuel, resulted in variability in annual arrival dates for individuals. The repeatability for the two sexes combined was 0.23.
  • Laying date was the least consistent stage of the annual cycle, with a repeatability index of 0.11 and no significant difference between males and females.

In an individual Whimbrel’s annual cycle, there appears to be one fixed point – departure from wintering ground in West Africa. With no discernible seasonality of resource availability on the wintering grounds and little change in day length in these areas, departure dates are probably being determined by an ‘internal clock’. Two major unknowns will then determine what happens in the next twelve months. Will wind and weather conditions be conducive to a one-leg flight to Iceland and how successful will a bird be in any particular breeding season? Unforeseen events, such as having to wait for a delayed partner, losing a first clutch, and the time needed to guard chicks will all affect the timing of autumn migration.

Understanding individuals

blog tag through grassThe study of wader migration has advanced hugely.

  • Fifty years ago, the main measure of migration phenology was the appearance of the first individuals of a species.
  • Colour-ring sightings are ideal for providing repeat arrival dates over the lifetimes of individuals, as exemplified by the Gill et al paper on Black-tailed Godwits, which suggest that individual timing is highly repeatable.
  • Geolocators have provided more detailed information about the precise arrival and departure timings of individuals, which is so important if we wish to conserve threatened, migratory species that visit areas in which data collection was previously virtually impossible.
  • Now, by tracking individual birds for several years, it is possible to look at the variability in annual patterns, and what can cause this variability.

Over the next decade or so, as devices get smaller and remote downloads become easier (eg using GSM tags), it should become possible to understand the conditions that lead to fast, slow and aborted migratory journeys in a whole range of species. Exciting times!

Paper

Why are Whimbrels not advancing their arrival dates into Iceland? Exploring seasonal and sex-specific variation in consistency of individual timing during the annual cycle. Camilo Carneiro, Tómas G Gunnarsson & José A Alves. Frontiers in Ecology & Evolution.

There is more about the information that is obtained from geolocators, how they work and the affects that they have on the individual birds that wear them in these two blogs:

blog roost flock


GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.

@grahamfappleton