Migration of Scottish Greenshank

In 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.

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.

The 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.

The Greenshank of Tongue

The 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.

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).

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

Colour-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

Although 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

The 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.

To 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.

• Green Sandpipers and geolocators
• Winter territories of Green Sandpipers

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.

• Mission impossible: counting Iceland’s wintering Oystercatchers
• Which Oystercatchers cross the Atlantic?

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:

• Travel advice for Sanderling

---

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

 

Where to nest?

There is nothing more obvious than an Oystercatcher sitting on his or her nest, but a brooding Snipe can be invisible until almost trodden upon. Which strategy works better: nesting in plain view but laying cryptically camouflaged eggs or hiding yourself and your nest in a clump of grass? Which species is most likely to hatch a successful brood of chicks and in what circumstances? In a 2020 paper in IBIS, Becky Laidlaw and colleagues analysed nest site characteristics and nest locations of 469 wader nests in Iceland in order to provide some answers

The perils of ground-nesting

Hatching Whimbrel eggs, with the tell-tale shell fragments that signal a nesting attempt has been successful

Almost all waders are ground-nesters, which makes them highly vulnerable to a wide range of nest predators. To reduce the risks of predation, different strategies have evolved. In some species, nests are placed out in the open, and the camouflage is provided only by mottled egg colouration that resembles the background. In other species, nests are secreted in vegetation, meaning eggs and incubating adults are concealed from predators.

In both groups of species, the risk of nests being predated might vary, depending on the surrounding habitat. For open-nesting species, for example, clutches that are laid in large patches of similar habitat may be harder for predators to locate. The same could apply to closed-nest species that hide their nests; Snipe nests may be tricky to find in extensive areas of long grass but perhaps more at risk if there are only a few suitable clumps of long grass that predators need to check out.

Iceland: a wader factory

As discussed in previous WaderTales blogs, particularly Do Iceland’s farmers care about wader conservation? Iceland is hugely important as a European ‘wader factory’. As farmland elsewhere has become less suitable for species such as Redshank and Snipe, the global importance of the country has increased (see table alongside for most recent figures from an AEWA report)  With this in mind, it is important to understand the factors that underpin the population dynamics of Iceland’s breeding waders.

Working in South Iceland, Becky Laidlaw and her co-authors tried to find as many nests as possible during the summers of 2015 and 2016. This area is largely a mosaic of open habitats, although there are more patches of forestry than there were twenty years ago. Most of the Southern Lowlands area is farmed, on a gradient between intensive and semi-natural, and this is reflected in the distribution of breeding waders (see Farming for waders in Iceland).

Dragging a light rope across the vegetation to flush nesting birds

For this project, nests were located by surveys from vehicles and on foot, through observation of incubating adults, systematic searching, incidental flushing of incubating adults and rope-dragging (dragging a 25 m rope, held between two fieldworkers, lightly across vegetation) to flush incubating adults.

The analysis in the resulting paper in IBIS focuses on 469 nests of three open-nesting species (Oystercatcher, Golden Plover and Whimbrel) and three species that hide their nests in tall vegetation (Redshank, Snipe and Black-tailed Godwit). The team recorded the habitat and vegetation structure around each nest (at the nest, within a 5 m x 5 m square and in a wider 50 m x 50 m square) and worked out which nests hatched successfully and which were predated. The date and time of predation were determined, where possible, with nest-cameras providing extra information for some nests. Cameras captured nest-predation events involving Arctic foxes, Arctic Skuas, Ravens and sheep.

Interestingly, 2015 and 2016 were very different wader breeding seasons. The graphic below shows the mean temperatures for the months from April through to July (encompassing the wader breeding season at this latitude) were much cooler in 2015 than in 2016, representing average monthly difference of between 1.5°C and 2.5°C. At high latitudes these figures translate into very different rates of vegetation growth.

First, find your nest

When nests were first located, their positions were marked and referenced using GPS. Eggs were floated in water to provide an estimate of laying date and thereby predict hatching date. As the chick develops within an egg, the density of the egg falls. A newly laid egg will lie on the bottom of the flotation vessel. Over the next few days the ‘blunt end’ rises until the egg is still touching the bottom but vertical. Eggs in the late-development stage float ‘point-end-down’, with the latest eggs floating at an angle to the vertical (method described by Liebezeit et al.).

This Golden Plover nest was probably predated by an Arctic Skua

Nests were considered successful if one or more eggs hatched, and predated nests were defined as those that were empty in advance of the predicted hatch date or those without any eggshell fragments in the nest (a sign of successful hatching). To determine the time and date of nest failures, iButton dataloggers were placed in a randomly selected subsample of nests. These loggers recorded a temperature trace every ten minutes. A sharp and permanent decline in nest temperature below incubation temperature indicates nest predation. In both study years, motion-triggered cameras were deployed on a sample of open-nesting species to determine the predator species active on these nests.

When each nest was first located, the percentage of eggs visible from directly above the nest was estimated and the habitat surrounding each nest was assessed in the field at three spatial scales: the nest cup, the 5 m x 5 m and the 50 m x 50 m area surrounding each nest. Details are in the paper.

Which nests survive through to hatching?

Over the breeding seasons of 2015 and 2016, the outcomes of 469 wader nests were assessed. 259 hatched successfully (55%), 192 were predated (41%), 13 were abandoned, 7 were trampled and 2 were mown. A nest-loss rate of 40% is fairly typical for ground-nesting waders, when compared to studies in different countries and habitats.

Daily nest predation rates did not vary significantly in relation to the habitat heterogeneity or the extent to which the dominant habitat covered the area surrounding the nest, at either 5 m x 5 m or 50 m x 50 m scales. Most clutches were laid in habitats that were the same or similar to the surrounding areas. Where there were differences, the dissimilarity between the habitat at the nest cup and in the surrounding area did not influence daily nest predation rates for open- or closed-nest species. Although nest predation is high, at about 40%, incidence of predation events appears to be unpredictable – or even random.

In cold spring conditions, Icelandic Snipe are not able to hide their nests

Daily nest predation rates were significantly higher for closed nests (Redshank, Snipe and Black-tailed Godwit nests) in which a greater percentage of the clutch was visible. This suggests that the onset and rate of vegetation growth could potentially constrain the availability of suitable nesting locations for these species, and hence influence nest success, particularly among early season nests. This has been studied in Icelandic Black-tailed Godwits by José Alves and colleagues and is described in From local warming to range expansion.

For closed-nest species, the visibility of nests was significantly greater during the early part of the 2015 breeding season, when compared to 2016, due to slower grass growth in cooler conditions.  The higher predation rate of more visible nests of closed-nesting species was apparent even though nests were predated up to three weeks after egg visibility was measured. These findings suggest that early nesting attempts by concealed-nest species are unlikely to be successful in years when vegetation growth is delayed or slow. There can be major benefits of hatching early, with recruitment into breeding populations typically being lower for later-hatched chicks, so vegetation growth rates are likely to be really important to species that conceal their nests (Redshank, Snipe & Black-tailed Godwit in this study). However, given the ongoing trend for warmer springs at subarctic latitudes, the conditions in which early nests can only be poorly concealed are likely to be reducing in frequency.

In summary

Golden Plover nest set within a homogeneous habitat matrix

Perhaps surprisingly, nest predation rates were similar for open-nest and concealed-nest species and did not vary with vegetation structure in the surrounding landscape. However, nest-concealing species were about 10% more likely to have nests predated when the nests were poorly concealed, and the frequency of poorly concealed nests was higher at the start of the breeding season in colder conditions.

The paper at the heart of this blog is:

Vegetation structure influences predation rates of early nests in subarctic breeding waders. Rebecca A. Laidlaw, Tómas G. Gunnarsson, Verónica Méndez, Camilo Carneiro, Böðvar Þórisson, Adam Wentworth, Jennifer A. Gill and José A. Alves. IBIS. doi:10.1111/ibi.12827

---

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

As 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.

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

Millions 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?

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.

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.

Migration

One 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

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 2^nd and 10^th 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.

Class of 2018

In 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

The 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

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.

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.

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 150^th 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.

---

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