A Rhapsody of Whimbrel

Around the globe, the seven-note whistle of the Whimbrel is a spring theme tune for shorebird migration. Where are flocks going to, as they gain height and head north in March, April and May, and why have birds chosen that particular moment to depart?

In a paper in Frontiers in Ecology & Evolution, Camilo Carneiro, Tómas Gunnarsson and José Alves analyse individual migration tracks of birds flying from West Africa to Iceland, including journeys made in successive springs by birds that have been part of the same study for several years. Can these birds help to explain how Whimbrel use time and weather cues in their travel ‘planning’ and might their plans change during the course of their lives?

Look up to the skies and see

Almost all of the Whimbrel that nest in Iceland migrate to West Africa after the breeding season, with just a tiny number wintering in Europe.

Life has just begun

The Whimbrel’s story starts in Southern Iceland. It would be great to tag chicks when they hatch, in order to learn what happens to juveniles in their first autumn, as they head south without parental guidance. For the moment, however, Camilo Carneiro, José Alves and Tómas Gunnarsson are focusing on parent birds which they have been catching on their nests since 2012.

The research summarised in the paper at the heart of this blog uses data from 66 retrieved geolocators that have been carried by a total of 39 individuals.  Light data, temperature readings, conductivity and the timing of contacts with water all help to determine the start and end points of individual flights.

Any way the wind blows?

As the authors write in the summary of the paper, “Weather conditions are important during migration, particularly wind and temperature, and can play a crucial role in the timing of events during the annual cycle of migratory birds.” Camilo and his colleagues have investigated how wind conditions, temperature and spring departure date may drive individuals to pursue either a ‘stop-over’ or ‘direct flight’ strategy in the spring. They suggest that one or two of the following scenarios might be envisaged:

Competition on the breeding grounds can be quite vigorous
  • Whimbrels may make migratory decisions prior to departure, given local weather conditions. If migratory behaviour is defined prior to departure then that would suggest that departure time from West Africa may not be associated with the wind conditions that can assist individuals on the first stage of their journeys.
  • Whimbrels may adjust migratory behaviour during flight, depending on conditions experienced en route. As birds fly north, from 37°N (level with the Mediterranean) to 50°N (SW tip of England), they can make decisions to stop off, rather than continue straight to Iceland. Potentially, they could assess the amount of support they have been receiving from favourable winds and assess the positive effect on fuel reserves. Temperature could also act a cue to weather conditions in Iceland.

Little high, little low

Wader biologists and birdwatchers will have seen flocks of waders preparing for departure from breeding, stop-over and wintering locations.  Birds become restless and groups of birds start to circle and rise into the sky.  The first, departing flock may be joined by others, taking off in small groups to catch up with birds that seem to have a plan. At the same time, birds can also be seen dropping out of the flock to wait for another day.

Once formed, a migratory flock will be made up of individuals that may be heading for points that are hundreds or (for some species) even thousands of kilometres apart but will fly together for this next leg of the journey.

Tómas Gunnarsson has seen Whimbrel circling and gaining height at departure from the south coast of Iceland in autumn, suggesting that they may assess wind conditions at different altitudes before making a final decision and setting their course south. It seems plausible that the same sort of thing might happen during spring migration from West Africa. At some stage, with a large number of tracked birds, perhaps it will be possible to study if waders sample wind speed and direction prior to departure and whether decisions made at this point affect the amount of support they receive from wind conditions when on migration. There’s a great paper about how wind affects the migration of much larger Honey Buzzards by Wouter Vansteelant.

Once in the air, birds in a migrating flock can be impeded by headwinds, assisted by tailwinds and pushed laterally by crosswinds. As has been shown when tracking trans-Pacific journeys of Bar-tailed Godwits, storms and pressure systems can provide a sling-shot effect to accelerate progress, cause birds to temporarily abort their journeys or even back-track a thousand kilometres, in order to refuel for another migration attempt.

Nothing really matters

Camilo and his colleagues compared 9 direct flights with 48 that included stops in Portugal, France, Ireland and north-west Britain. Birds that departed later tended to undertake direct flights. Interestingly, they found little evidence that conditions were linked to an individual’s migration option:

  • For individuals undertaking either direct flights or stopovers, the wind conditions at departure did not differ from winds during the previous seven days, suggesting little or no selection for wind conditions to initiate the flight.
  • Individuals on direct flights encountered similar winds as they passed through the region 37°N to 50°N (Mediterranean to SW tip of England) as those on stop-over journeys.

Too late, my time has come?

For late-departing birds that fly straight to Iceland, there is the potential to catch up with (and even overtake) birds that left earlier and subsequently stopped in countries such as Ireland. In such circumstances, one could imagine that birds still in West Africa in late spring may ‘opt’ for a direct flight. However, the wind patterns over a period of seven days prior to departure were no different to the ones at the start of a non-stop flight. There did not seem to be any weather-related reason for these birds delaying departure as long as they did.

This image has an empty alt attribute; its file name is blog-camillo.jpg
Camilo Carneiro is also investigating the breeding success associated with different arrival times and migration patterns

For birds that do stop-off en route in Britain and Ireland, which are relatively close to the breeding sites in Iceland, there are potential benefits, as discussed in more detail in the paper:

  • Individuals might be able to assess (remotely) the weather conditions at their breeding sites if there are links between weather patterns in Iceland and those in Ireland and western Britain. If this is the case, then they can adjust the start of the final Atlantic crossing so as to arrive in Iceland when conditions are likely to be favourable.
  • Whimbrels can feed up in Britain & Ireland, potentially arriving in Iceland in better condition than birds that have flown directly from West Africa.

Carry on, carry on

The fascinating thing about being able to track individuals is that we are starting to understand the conditions that may lead to the migration patterns we see at the population level. In other WaderTales blogs, some of the key processes and patterns have already been discussed:

Given this body of knowledge, suggesting little flexibility once an individual’s phenology is fixed, one might expect that an individual Whimbrel, travelling from West Africa to Iceland, would adopt the same migration pattern in subsequent years. Tagged Whimbrels, for which there were repeat migration tracks, mostly ‘did the same’ but not always.

Any way the wind blows, doesn’t really matter

The key finding of Camilo Carneiro and his colleagues is that weather conditions are not the main driver of different spring migratory timings in Icelandic whimbrels. As suggested in Whimbrel: time to leave (and the paper Why are Whimbrel not advancing their arrival dates into Iceland?) departure from West Africa is the most firmly scheduled point in a Whimbrel’s annual cycle. However, three birds provide an opportunity to build a modified hypothesis.

In the course of this study of Icelandic Whimbrel, thirteen birds have provided multiple years of data and there have been three cases in which birds have switched migratory behaviour, seemingly contradicting the ‘birds always do the same thing’ theory. In each case, individuals changed from ‘direct-flight’ to ‘stop-over’ and, having changed, they then repeated the ‘stop-over’ option. The fact that all three individuals made the same change hints towards individual refinement of behaviour. Since there appears to be no clear advantage to direct migration, perhaps individuals are moving to a two-stage migration when they discover that this is a possibility?

Is this just fantasy?

This is where the paper stops but it will be fascinating if the research can continue:

  • Are changes always going to be in the same direction – from ‘direct-flight’ to ‘stop-over’?
  • Most juveniles are thought to fly directly to West Africa. By tracking young birds, caught in Iceland prior to departure, perhaps it will be possible to work out the proportion of first journeys that are direct?
  • Young birds that fly south across the Atlantic will not have learnt that there is any land between Iceland and West Africa. Do they retrace their journeys when they fly north again, eighteen months later?
  • What proportion of these birds that start on the ‘direct-flight’ strategy later switch to ‘stop-over’?
  • If some juveniles stop off in western Europe, on their first journeys south, perhaps these birds also stop off on their first journeys north? That might mean that they never used the ‘direct-flight’ option.
  • And how do flocks work? Will it ever be possible to deploy enough trackers to see whether ‘direct-flight’ individuals learn that there’s an alternative option by travelling in flocks with birds that use the ‘stop-over’ strategy.

It’s all fascinating stuff about the Queen of waders!

This image has an empty alt attribute; its file name is blog-take-off.jpg

Anyone can see

The paper featured in this blog is: Linking weather and phenology to stopover dynamics of a long-distance migrant by Camilo Carneiro, Tómas G. Gunnarsson & José A. Alves, published in Frontiers in Ecology & Evolution.


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

Where to nest?

pic whimbrelThere 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

pic hatching whimbrel

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.

pic hidden Redshank

Iceland: a wader factory

tableAs 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).

pic rope

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.

pic pretty graph

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.).

pic skua-ed goldie eggs

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.

pic fox attack

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.

pic snipe nest

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

pic goldie nest in habitat

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

pic sheep


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?

blog isotope chest

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.

blog snow

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

Migrant or resident?

blog co sligo

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).

blog pie charts

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 

blog footer


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

 

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

 

 

 

January to June 2019

blog CU postOne or two WaderTales blogs are published each month. The series is UK-based with a global reach. Suggestions of newly-published research on waders that might be of interest to birdwatchers who appreciate waders/shorebirds are welcomed. I am particularly keen to give feedback to colour-ring readers; they provide a huge amount of information that lies at the heart of these stories.

Click on a link in bold to read an individual blog.

You can sign up to receive an e-mail notification when a new blog is published.


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.

Designing wader landscapes

blog whimbrelMuch has been written about the negative impacts of agriculture on breeding birds – but farming can be good for some species. In Iceland, where high-input agriculture is relatively recent, breeding waders are commonly found in nutrient-rich environments that are associated with increased production. How can high breeding densities of waders be maintained, as farming continues to expand and intensification increases?

In her paper in Agriculture, Ecosystems & Environment Lilja Jóhannesdóttir investigates the distribution of breeding waders across landscapes with varying amounts of highly-cultivated fields and semi-natural areas. She discovers that, in some circumstances and at an appropriate level, adding cultivated land within a broader mosaic of habitats may benefit breeding waders. Is this a model system that provides clues as to how to design landscapes that can support sustainable breeding wader populations in other parts of the world?

The waders of Iceland

table

Breeding populations of waders in Iceland (AEWA report)

Iceland is a hot-spot for breeding waders, holding half or more of Europe’s Dunlin, Golden Plover and Whimbrel, in a country that is a bit smaller then England. The paper at the heart of this blog is written by Lilja Jóhannesdóttir, who worked with colleagues from the University of Iceland, the Agricultural University of Iceland, the University of East Anglia (UK) and the University of Aveiro (Portugal). They investigated how different ways of increasing agricultural productivity might impact upon these species, and others such as Black-tailed Godwit, Redshank and Snipe.

Much of Iceland’s upland interior is not suitable as farmland but there is still plenty of room for agricultural expansion. Only 7% of the area between sea level and an elevation of 200 m is currently under cultivation but it is estimated that it would be possible to increase this to 63% – an eight-fold extensification. Icelandic lowlands currently comprise a fine-scale mosaic of open semi-natural habitats and cultivated fields (primarily for silage production to feed animals), making most of the landscape much more heterogeneous than in countries with a longer history of commercial farming.

blog hay and semi-naturalTwo previous WaderTales blogs have already shown that:

Given that farm production is predicted to increase, that farmers like breeding waders and that some intensively-managed fields can be attractive to waders, is it possible to design farmed landscapes that will work for birds and farmers?

Increasing inputs and reducing heterogeneity

blog nice wetlandGlobally, the expansion and intensification of agriculture has altered landscapes and the associated homogenisation has greatly influenced bird abundance and reduced biodiversity. Populations of numerous species, particularly specialist species, have declined, as agriculture has expanded, while generalist species have often thrived in agricultural habitats.

There is no shortage of examples in which highly intensively managed farmland is shown to be bad for breeding waders. In the monoculture hay-meadows of the Netherlands, Black-tailed Godwit productivity is really low, for instance. These fields have been drained, fertilised and re-sown, in order to create easily-managed carpets of single-species grass that can be cut several times a year. There is more about this in this paper by Roos Kentie.

blog hay fieldAlthough there are some areas of Iceland in which farming is quite intensive, there are many others where farmers have a lighter touch. For instance, nutrient-poor dwarf birch marshes may occasionally be grazed by sheep in the summer but these areas have never received applications of artificial fertiliser. At this end of the intensification continuum, increasing agricultural operations may have benefits for breeding waders. When a patch of rough grazing is ploughed and turned into a hay meadow, the addition of fertilisers can potentially increase soil fertility and create an attractive place for waders to feed. A hay meadow within a local area that is dominated by dwarf birch marsh could effectively increase the heterogeneity (& nutrient-richness via spill-over) of the local area, albeit in an artificial way. In the UK, Golden Plovers breeding on moorland are known to travel up to 7 km to feed on fertilised hayfields with high earthworm densities. This paper by James Pearce-Higgins & Derek Yalden in IBIS provides a nice example of how low intensity agriculture can provide resources for waders in the wider landscape.

Researching waders and landscapes

blog dbmLilja’s work in the Southern Lowlands of Iceland focused upon understanding how agriculture influences breeding wader densities and how these relationships might influence future change. At its heart were counts of adult waders encountered along 200 transects (totalling over 100 kilometres) within semi-natural habitats, visited at several stages during the breeding seasons of 2011 and 2012.

As well as counting birds, Lilja categorised habitats within 500, 1000, 1500 and 2500 metres of the transects, which she called buffer area in the paper. Interestingly, and usefully for later analyses, the distribution of different habitat types is pretty uniform across these scales, in this part of Iceland, with little substantial difference according to elevation. In the diagram below, the 200 transects (a) have been split between those below 50 m above sea level (b) and those higher than 50 m (c).

buffers

Landscape-scale effects

To fulfill the various demands of parents and their offspring, waders need diverse resources on or near their territory. An adult can feed a kilometre or more away from its nest, between incubation bouts, and chicks are mobile from an early age. Tagging has shown that young Black-tailed Godwits can move up to 3 km in the first five days of life, just to give one example. In this open landscape, breeding success is likely to be a function of habitat availability at a broad scale. This is explored in a WaderTales blog about nesting Whimbrel.

blog redshankUsing data collected from these 200 lowland transects, Lilja was able to establish relationships between breeding wader densities and the amount of cultivated land and wetland in the surrounding landscape. These two habitat types were considered because future agricultural expansion is likely to take place on drained wetlands that have high conservation value. In her analyses she assessed the extent to which the amount of cultivated land in the surrounding landscape affects wader densities on semi-natural land, and then considered the potential effects of future agricultural expansion on wader populations. There was substantial variation in the density of all of the six most common wader species recorded on the transects, ranging from 0 to 284 birds/km2.

Lilja found that wader densities in semi-natural habitats were consistently greater when the surrounding landscapes had more wetland, at scales ranging from 500 m to 2500 m, indicating the importance of wetland availability in the local neighbourhood. However, the effects of cultivated land in the surrounding landscape varied with fertility and landscape structure, which was largely defined by altitude.

  • In fertile, low-lying coastal areas (from sea-level to 100 m altitude), wader numbers declined with increasing amounts of cultivated land (and the lowest densities occurred in areas dominated by cultivation). This suggests that further conversion of semi-natural habitats into farmland is likely to severely impact waders in low-lying areas.
  • In less fertile habitats at higher altitudes (between 100 m and 200 m), the lowest densities occurred in areas without cultivated land. This suggests that additional resources provided by cultivated land may have a more positive affect in the less-fertile, higher altitude areas.

blog blackwitThe relationships between the areas of wetland and agriculture in the surrounding landscape and the density of waders vary between species, as you can read in some detail in the paper. A few highlights are:

  • With increasing area of cultivated land, densities of Golden Plover, Dunlin and Whimbrel declined significantly at lower altitudes but increased at higher altitudes. These are the three species that would appear to respond most positively to the addition of pockets of cultivated land within a semi-natural matrix of less fertile land, that tends to be found at higher elevations.
  • Higher amounts of wetland were associated with increased densities of Dunlin and Black-tailed Godwit, but lower densities of Redshank. Golden Plover numbers were unaffected by amount of wetland in the surrounding landscape.
  • Whimbrel densities increased with wetland area, at higher altitudes. Wet patches have been shown to be very important to Whimbrel chicks, as you can read in this WaderTales blog about research in Shetland.
  • At lower altitudes, Snipe densities increased with the amount of wetland area in the local vicinity. This relationship was less pronounced at higher altitudes, which tend to be less effectively drained and hence generally wetter.

dunlin graphic

What now?

Changes in Icelandic landscapes are to be expected in the coming years, as most farmers intend to increase their areas of cultivated land. This expansion will inevitably have impacts upon the internationally important breeding wader populations of Iceland but the level of such impact will depend on where the expansion will occur. This paper shows that increases in the area of cultivated land at lower altitudes in Southern Iceland are more likely to result in declines in wader density than in less fertile areas, when tend to occur at slightly higher altitudes (still under 200 m above sea level). An important next step will be to identify the landscape structures and scales of management that can continue to support high densities of breeding waders.

blog coastal wetlandGiven the international importance of Iceland as a home for breeding waders it would be nice to think that this paper can be used to develop national land management policies that can prevent the unintended loss of species such as Golden Plover and Snipe, which landowners value and wish to preserve. At the farm and community level, the paper highlights the key importance of maintaining the complex and heterogeneous landscapes of lowland Iceland, retaining as many as possible of the remaining wetland patches and pockets of semi-natural land within even the most intensive of farming areas.

The paper may well be of interest to conservationists who are struggling to reverse wader declines in other parts of the world. In Southern Iceland, where 7% of the land is being farmed relatively intensively within a fine scale mosaic of both wet and dry semi-natural habitats, it is possible to support hundreds of waders per square km across the wider countryside. Can this situation be replicated across large tracts of land in other countries?

Take home message and paper

blog heterogeneousThis paper provides a useful reminder that the links between land use changes and biodiversity implications can be highly context-dependent. Further agricultural conversion of wetlands and rough grazing areas in the fertile low-lying areas of Iceland is likely to be detrimental for breeding waders, but such effects may be less apparent in less fertile, higher altitude areas. Here, the conversion of some land from rough-grazing to hay meadows may provide feeding opportunities off-territory for Dunlin, Golden Plover and Whimbrel. The scale at which the addition of cultivated areas is beneficial to breeding waders has yet to be determined.

This paper is published as:

Interacting effects of agriculture and landscape on breeding wader populations. Lilja Jóhannesdóttir, Jennifer A. Gill, José A. Alves, Sigmundur H. Brink, Ólafur Arnalds, Verónica Méndez and Tómas Grétar Gunnarsson https://doi.org/10.1016/j.agee.2018.11.024

blog end banner

 


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.

 

Iceland to Africa, non-stop

blog tagRinging had already suggested that Whimbrel might fly non-stop from Iceland to western Africa (see “Whimbrels on the move”). By using geolocators, Camilo Carneiro and his colleagues from the Universities of Iceland and Aveiro (Portugal) have now shown that this is the norm – and reveal just how quickly they get there.  In the paper reporting on this work, they contrast this rapid autumn movement with what happens on the return journey in spring.

Migratory journeys

European Whimbrel are made up of two distinct populations which mix in the wintering grounds. Three-quarters of the estimated total of 400,000 pairs breed in Iceland, with the rest breeding from Scandinavia through to Russia. In the autumn, most of the Icelandic birds fly straight to Africa. In the late summer and early autumn, the vast majority of birds seen in the UK and other European countries on the East-Atlantic Flyway are of continental (rather than Icelandic) origin. Most will continue their migrations to Africa.

Camilo Carneiro’s paper focuses on the Icelandic population. Although the breeding locations of the birds in the study all fell within a circle of radius 5 km, the wintering area represents about 1500 km of the coastal strip of western Africa and its off-shore islands. This includes Sierra Leone, Guinea-Conakry, Guinea-Bissau, Senegal, The Gambia, Mauritania and Morocco, with the highest density of the locations in Guinea-Conakry and Guinea-Bissau. On spring migration, although some manage a similar non-stop flight, most birds stopped off on their way back to Iceland. The largest number paused in Ireland, with others visiting western Britain, northwest France and Portugal. Marked birds flew an average of 6079 km in autumn and 6450 km in spring.

blog graphic

A sense of urgency

Most studies show that birds migrate faster in spring than in autumn, something that may be associated with a need to get to breeding sites as quickly as possible. Potentially, this enables them to take advantage of the short window in which to find a partner, lay and hatch eggs, look after chicks and fatten up for the return journey. Why is autumn migration quicker for Whimbrel that breed in Iceland and spend the winter in countries such as Guinea-Bissau?

blog tag postCamilo Carneiro and his colleagues have been studying the migrations of individual Whimbrels using geolocators. These small devices, attached to leg-rings, record the times of dawn and dusk for twelve months. When (or if!) an individual can be caught again in the subsequent breeding season, the geolocator can be removed and the data down-loaded, revealing a year’s worth of movements. One of the fascinating things about this study is that there are 56 migrations from 19 individuals; meaning that there are several birds for which repeat information has been collected. There’s a WaderTales blog about geolocators here (Are there costs to wearing a geolocator?)

The tags used on these Whimbrels did not just measure light levels, they also recorded temperature and whether the tag was wet or dry. These extra data helped to establish more precisely the periods in which birds were on migration, as air temperature is lower at higher altitudes and tags can only record wetness if birds are standing in water. Please see the paper and supporting materials for details of the methodology. Given that birds cannot fly without fuel, account is taken of the time taken to fatten up for migration, when estimating the whole migratory period.

blog banner africa

Wintering Whimbrel in Guinea-Bissau

Results

The paper by Camilo Carneiro in the Journal of Avian Biology provides details about the wintering and staging location of Icelandic Whimbrel but the main focus is on speed of migration. This was calculated as the ground distance travelled divided by migration duration, where this period includes fuelling time.

  • blog flightAll birds flew directly from Iceland to the wintering sites (30 autumn migrations from 19 individuals), a journey of four or five days.
  • Males departed earlier than females in spring and made a stopover in 83% of the cases (15 out of 18 individuals), while females stopped on 75% occasions (6 out of 8).
  • Migration duration (fuelling plus flight times combined) was significantly different between seasons, being 59.2 ± 6 days in autumn and 65.5 ± 6.2 days in spring, with no apparent differences between sexes.
  • Migration speed and ground speed were higher in autumn than in spring (migration speed: 102.6 ± 2.2 kmd-1 in autumn and 98.6 ± 5.3 kmd-1 in spring; ground speed: 16.50 ± 5.99 ms-1 in autumn and 13.07 ± 5.82 ms-1 in spring), with no differences between sexes.

blog tag in grass

Catching an individual Whimbrel, in order to remove its geolocator, becomes harder every year. A range of methods is used to catch birds on their nests.

With only a small sample, the following reported results were not statistically significant:

  • On average, males departed later than females on autumn migration. This makes sense, as males stay with their chicks longer than females.
  • In spring, males arrived into Iceland on average 2 days before females.

Explaining the patterns

The discussion section of the paper provides a fascinating review of some of the theories relating to migration physiology – it’s well worth a read. This is just a quick summary.

Autumn migration seems relatively straightforward; every tracked Whimbrel took a direct flight from Iceland to Africa. For Whimbrel migrating to Iceland from western Africa in spring, however, there seems to be a relatively small chance of being able to fly all the way in one hop (5 out of 26 northward flights were direct). The authors suggest that:

  • blog mangrove

    Whimbrel roosting in the top of mangroves at high tide

    When leaving Iceland at the end of the summer, Whimbrel are heading towards predictable resources which will be similar from week to week. Timing of departure is not critical and birds may be able to wait for helpful weather patterns.

  • On the journey south, wind conditions are generally more favourable than on the journey north, reducing the duration of direct flight.
  • Some birds may have sufficient resources for the northward flight, if weather conditions are helpful, but choose to stop off in western Europe (particularly Ireland) if the fuel gauge suggests that they might not be able to complete the crossing.
  • It is possible that the relatively recent addition of West African Bloody Cockles to the Whimbrel’s diet, in the Banc d’Arguin, may have improved the species’ capacity to fatten up quickly, increasing the possibility of a one-flight trip north.
  • Staging areas in western Europe, particularly Ireland, may provide relatively predictable resources that can be used to top-up reserves for the final 1500 km crossing of the Atlantic in spring. By using a stop-over, it may be possible to take on extra reserves that can be used in the early part of the breeding season.
  • There may be a stronger link between weather patterns in western Europe and Iceland than between western Africa and Iceland. Whimbrel that stop off in Ireland, or other countries on the Atlantic seaboard, may then depart in weather systems that are also associated with warmers spring conditions in Iceland.

blog no ringThere are many questions still to be answered but one thing is certain; as it says in the title of the paper, when the migration of the Icelandic Whimbrel is studied in detail, it is clear that there is faster migration in autumn than in spring. Here’s a link to the paper:

Faster migration in autumn than in spring: seasonal migration patterns and non‐breeding distribution of Icelandic Whimbrels Numenius phaeopus islandicus Camilo Carneiro, Tómas G. Gunnarsson & José A. Alves Journal of Avian Biology 10.1111/jav.01938

More about migration

Migrating birds make ‘decisions’ on timing and staging each year that can affect their personal survival and the chance of successfully raising young. Are these ‘strategies’ just the consequences of the circumstances that arise in a particular season? As scientists gather longer runs of tracking data on individuals, and can relate these to wind and weather patterns, it may be possible to gain a better understanding of the drivers of migratory patterns.

The team behind this paper (Camilo Carneiro, Tómas Gunnarsson & José Alves) have produced a number of complementary papers on wader migration, some of which have been covered in previous blogs:

WaderTales: Overtaking on Migration.  Alves, J. A., Gunnarsson, T. G., Potts, P. M., Gélinaud, G., Sutherland, W. J. and Gill, J. A. 2012. Overtaking on migration: does longer distance migration always incur a penalty? – Oikos 121: 464–470.

IBIS/BOU: Risking it all in a direct flight.  Alves, J. A., Dias, M. P., Méndez, V., Katrínardóttir, B. and Gunnarsson, T. G. 2016. Very rapid long-distance sea crossing by a migratory bird. – Sci. Rep. 6: 38154.

Gunnarsson, T. G. and Tómasson, G. 2011. Flexibility in spring arrival of migratory birds at northern latitudes under rapid temperature changes. – Bird Study 58: 1–12.

WaderTales: Whimbrels on the move.  Gunnarsson, T. G. and Guðmundsson, G. A. 2016. Migration and non-breeding distribution of Icelandic Whimbrels Numenius phaeopus islandicus as revealed by ringing recoveries. – Wader Study 123: 44–48.

WaderTales: Black-tailed Godwit pairs – the importance of synchrony.  Gunnarsson, T. G., Gill, J. A., Sigurbjornsson, T. and Sutherland, W. J. 2004. Arrival synchrony in migratory birds. – Nature 413: 646.

blog Iceland banner

The southern lowlands of Iceland (breeding grounds of Whimbrel) seen from Þríhyrningur

 


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.

 

 

 

Starting moult early

In waders (shorebirds), the main moult (molt) usually takes place after the migration that follows the breeding season. Golden Plovers adopt a different strategy, starting wing moult while still nesting. Given that these adult birds are not going to fly anywhere any time soon, this seems like a very efficient strategy. So, why do Icelandic and Scandinavian Golden Plovers moult differently? Is this a reflection of available resources?

The post-breeding moult

MOULT CYCLEMoult is an energetic process, especially the post-breeding moult, which includes a change of all of the wing and tail feathers. To complete the whole process, birds ideally need to find a three-month period when resources are good, climatic conditions are benign and there is no need to migrate. For birds on the East Atlantic Flyway that spend the non-breeding season in Europe, moult typically takes place after the breeding season and before days get shorter and the weather gets colder.

One place with plenty of food-rich mud is the Wash, in eastern England. Here, up to 300,000 waders gather each autumn, including Knot from Greenland and Canada, Grey Plover from Siberia and Curlew from countries such as Finland. A relatively small proportion are juveniles, which will only moult their body feathers, but there are probably at least 200,000 waders in full moult at this time of year – dropping and growing a grand total of perhaps a billion feathers between them. Some populations use the Wash as a feeding station, before moving on to moult in their wintering grounds, but this is a minority. This group includes taymyrensis Bar-tailed Godwits (more about these birds here) and schinzii Dunlin, which will travel further south, to Africa.

wing moult

Golden Plovers start their moult during or before the incubation period

There are Golden Plovers spread across the autumn mud-flats of the Wash too, made up of a mixture of birds that have bred in Britain, Europe, Scandinavia and Iceland. Although they end up in the same winter flocks, their moult strategies are different. Recent research by Paula Machín and colleagues has focused upon how breeding season conditions impact upon the moult strategy of two distinct Golden Plover populations, birds breeding in Scandinavia and Northern Russia and others breeding in Iceland. The resulting paper is published in the Journal of Avian Biology.

Conditions at the breeding grounds and migration strategy shape different moult patterns of two populations of Eurasian golden plover Pluvialis apricaria Paula Machín, Magdalena Remisiewicz, Juan Fernández-Elipe, Joop Jukema & Raymond H.G. Klaassen

Icelandic Golden Plovers

scopeUp to one million Golden Plovers arrive in Iceland each spring, mainly from Ireland and western parts of the United Kingdom. This is estimated to be nearly half of the European breeding population. Iceland might seem small, when compared to the vast land-mass of the European continent, but it’s a haven for waders. This status is threatened by the spread and intensification of lowland farming, increased afforestation and by the ‘summer cottage’ industry – but those are stories for another day.

eggsThe Heiðlóa (Golden Plover) is a welcome sight and sound at the end of the Icelandic winter. The first migrants appear about 23 March and nesting can commence as early as 26 April. The usual clutch size is four eggs, with both parents sharing incubation duties. Some first nests are lost, due to predation, but females can lay another clutch. Joop Jukema studied Golden Plovers nesting near Selfoss in the Southern Lowlands of Iceland, timing his captures of nesting birds to coincide with the later part of the incubation period. He was able to assess the progress of moult by scoring the growth of the primary feathers and to work out when each bird would have dropped its first primary. The estimated mean start date of primary moult for males was 19 May (95% confidence interval 27 April – 10 June) with females starting an average of 9 days later, on 28 May (95% confidence interval 6 May – 19 June). On average, males started to moult their primary feathers nine days before the start of incubation, while females started to moult at the same time as incubation began. Potentially, hormone changes associated with the stage of the breeding season could be linked to the onset of moult.

moult graphic

Icelandic Golden Plovers complete their moult prior to departure from the country. By making catches of birds in late August and early September, it was possible to show that the primary moult period is about 100 days. No birds were caught in suspended moult, strongly suggesting that Icelandic Golden Plovers do not attempt to cross the Atlantic before they have attained a complete, fresh set of feathers.

Swedish Golden Plovers

Paula Machín’s main study site was in Ammarnäs in Sweden, on roughly the same latitude as Selfoss and hence with the same amount of daylight. Ammarnäs is colder in spring than Selfoss, not benefiting from the warmer waters of the Gulf Stream which wash the shores of southern Iceland. The average start of incubation in Ammarnäs was eight days later than in Selfoss with the commencement of moult being seventeen days later. Males started primary moult three days after the start of incubation, with females starting twelve days into incubation. It is interesting to note that the difference in timing of the two sexes is nine days, just as in Iceland.

chickFemale Golden Plovers left the Ammarnäs breeding territories at the end of July. From observations of females caught on their nests, it seemed likely that individual females were not starting the moult of their outer primaries, typically completing the moult of primary four and not dropping primary five. Males stayed with chicks for an extra fortnight. Given the longer period of time available to males, it is likely that they were able to moult more primary feathers than their partners, prior to departure from the area.

Catching birds during the chick-guarding phase or just before migration is very difficult but Raymond Klasssen and colleagues were able to study birds on similar strategies by catching birds at Lund, in southern Sweden, and in the Netherlands. Here, birds from Swedish breeding areas and further afield gather to moult, recommencing primary moult at the point at which it had been suspended. Inspecting moulting birds in the period August through to November enabled the research team to monitor the second part of the moult of Continental birds. Given that the distance between breeding areas and these staging areas is relatively short and that tracking showed that it could be completed in one or two days, it is possible that adults might be able to migrate while in active moult.

Spot the difference

measuringOverlapping the breeding and moulting period is rare in migratory birds but it makes sense in a time-constrained annual cycle. The research team suggest that Icelandic plovers presumably need to initiate moult early in the season, in order to be able to complete it at the breeding grounds. This is not an option for Continental plovers, as their breeding season is much shorter, due to a harsher climate and an earlier drop-off in the number of arthropods, their main food source. These Golden Plovers cannot delay the start of the moult period until after the autumn migration because there is insufficient time to compete a full moult in areas such as Lund or the Netherlands, prior to the onset of winter frosts. The fact that Golden Plover are largely associated with farmland, rather than estuarine sites, may make them more susceptible to sub-zero temperatures than, for instance Grey Plover.

When incubating and looking after chicks, Icelandic and Swedish Golden Plovers were able to moult at the same rate. However, there were differences in the second part of the primary moult season. Away from their territories, Icelandic birds continued to moult at the same rate as previously but, having moved to Lund or the Netherlands, Continental birds could moult twice as fast as before. The availability of earthworms in these staging areas may make it easier to acquire resources for the energetically-expensive moult process.

TGG flying

Despite the faster rate of moult of Continental birds in the later period of their moult, the total period of primary moult is longer than that of Icelandic birds. Birds completing their moult in Iceland took an average of 100 days to replace their primaries, whilst Swedish-breeding birds took 16 days longer. This difference may be associated with the time taken to complete the first stage of moult, prior to the migratory flight away from the breeding sites.

alarmA key finding of this paper is that splitting the moult period extends the total period of primary moult. For Swedish breeders, this is the best option, however, as there is insufficient time to complete autumn moult close to the breeding grounds or after the breeding season. As the authors conclude, “Meeting the energy demands of breeding, moult, and migration calls for different timing and spacing of these events in their annual cycle, adjusted to conditions at their breeding and stopover sites, and to their migration strategy.”

There’s more from Paula Machín and her colleagues on this blog-site: https://overthetreeline.wordpress.com/

More moult

There are more WaderTales blogs about moult: 

  • The not-so Grey Plover includes general information about wader moult and talks about some of the stresses that may occur.
  • Lapwings can moult while on migration. Read more in Lapwing Moult, which also talks about how to study moult without catching birds.
  • Bar-tailed Godwit; migration and survival mentions the different strategies of two subspecies of Bar-tailed Godwit, both of which can be found on the Wash in autumn.

I look forward to future papers about moult strategies to add to WaderTales. Here’s a list of the 60+ blogs that are already available: https://wadertales.wordpress.com/about/

ugo banner


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.

 

 

Mission Impossible? Counting Iceland’s wintering Oystercatchers

If Norwegian Oystercatchers migrate south and west for the winter, how is it that thousands of Oystercatchers can adopt a stay-at-home strategy in Iceland, which lies at a higher latitude than most of Norway?

Braving the cold

As part of a project to try to understand why some Oystercatchers spend the winter in Iceland, when most fly south across the Atlantic, researchers needed to count the ones that remain. Unlike in the UK, where the Wetland Bird Survey can rely on over 3000 volunteers to make monthly counts of waders and waterfowl, it’s tough to organise coordinated counts of waders in Iceland. Winter weather, a small pool of birdwatchers and short days don’t help when you are trying to cover the coastline of a country the size of England.

blog wading

Up until 2016, the only winter wader data in Iceland came from Christmas Bird Counts, first run in 1956. These coordinated counts suggested that most Oystercatchers were to be found in southwest and west Iceland, which is also where most birdwatchers live, but with smaller numbers in areas such as the southeast. The maximum number of Oystercatchers found in any one year was 4466 birds but this excluded known wintering sites which were inaccessible or very hard to access. Some contributors to Christmas bird counts live in areas away from the well-populated west of the country, and they provided evidence that there were no Oystercatchers in the north, for instance. This information gave some guidance as to where to look for Oystercatcher flocks but could a small team of researchers and birdwatchers do a complete count of the resident component of the species in the middle of winter?

Blog snowy

 

Part one of the survey involved a group of well-prepared birdwatchers and researchers spending several days counting Oystercatchers in as many areas as possible of the southeast and in the whole of the west, from the southwest tip of Iceland (where Keflavik airport is situated) through to known wintering locations in the northwest fjords. The north and south coasts could largely be discounted; the north is too cold and the south coast is very barren.

Part two of the survey was carried out by air, allowing the addition of counts of the islands and inaccessible coastal sites in the Breiðafjörður Bay, as well as some key sites in Faxaflói Bay (see map). Flocks of roosting Oystercatchers were usually seen from afar and photographs were used to make counts without flushing the birds.

blog counts

Survey results

The ground-based wader surveys were carried out between 28 January and 3 February 2017 and the aerial survey took place on 16 February. In total, 11,141 Oystercatchers were counted, which nearly triples the previous Christmas total. As expected, the vast majority of Oystercatchers were found on wintering sites in SW and W Iceland. Large numbers of birds were found on sites not covered by the Christmas counts, particularly on the north side of Faxaflói Bay and during the aerial survey over Breiðafjörður Bay.

blog BoddiThe full results of the paper are presented in a new paper in the BTO journal Bird Study. (Click on title for link)

Population size of Oystercatchers Haematopus ostralegus wintering in Iceland Böðvar Þórisson, Verónica Méndez , José A. Alves, Jennifer A. Gill , Kristinn H. Skarphéðinsson, Svenja N.V. Auhage, Sölvi R. Vignisson, Guðmundur Ö. Benediktsson, Brynjúlfur Brynjólfsson, Cristian Gallo, Hafdís Sturlaugsdóttir, Páll Leifsson & Tómas G. Gunnarsson.

Resident or migrant? 

One of the key questions that researchers wanted to answer was ‘what proportion of the Icelandic breeding population is migratory?’ This is part of a bigger project exploring the causes and consequences of individual migratory strategies, as you can read in the previous WaderTales blog: Migratory decisions for Icelandic Oystercatchers. This project is a joint initiative by the universities of Iceland, East Anglia and Aveiro, led by Verónica Méndez.

blog familyIn order to estimate the proportion of migrants and residents it was necessary first to determine the total size of the Icelandic Oystercatcher population, based on a recent estimate of 13 thousand breeding pairs (Skarphéðinsson et al. 2016) . How many sub-adults are there to add to the 26,000 breeding birds?

Verónica Méndez and her team have shown that Oystercatchers fledge on average about 0.5 chicks per pair. Using estimates that 50% of these chicks are alive by mid-winter, that there is then a 90% chance of annual survival and birds typically breed when they are four years old, it was possible to come up with a total population of just over 37,000 birds.

Although the authors of the paper have produced the best winter estimate thus far, they note that it is a minimum – there could be small numbers of birds in other areas. At 11,141 out of 37,177 birds, the minimum estimate of the residential part of the population is 30%, leaving 70% to be distributed around the coasts of the British Isles and (in smaller numbers) along the coastline of mainland Europe.

Latitudinal expectation 

blog ringed birdTo put the migratory status of the Icelandic Oystercatcher into context with other Oystercatcher populations breeding in NW Europe, the authors collated information about the proportion of resident and migratory Oystercatchers in coastal countries between Norway and the Netherlands. They show that there is a strong latitudinal decline in residency. From Northern Norway (69.6°N) to Southern Sweden (57.7°N), where mean January temperatures are typically in the range of -1 to -4°C, only occasional individuals are found in winter, whereas populations in Denmark (55.4°N), where mean January temperatures 0.8°C, and sites that are further south and warmer mostly comprise resident individuals.

blog scenicThis cline in migratory tendency is also seen within the British Isles, which stretch from 60.8°N to 50.2°N. Writing in the BTO’s Migration Atlas, Humphrey Sitters reports that birds from the north of the British Isles have a median recovery distance of 213.5 km, whereas in the west, east, south and Ireland the respective figures are 35.5, 27.0, 6.0 and 13.5 km. In each group, there are birds that travel over 800 km, implying some degree of migratory tendency in birds breeding in every part of the British Isles.

Iceland lies between 63.2°N and 66.3°N, which puts it well within the latitudinal range of the ‘almost-all-migrate’ group of Scandinavian birds. The Icelandic proportion of 30% residency is likely to be a function of the temperature and geographical isolation of the island. Bathed by the relatively warm waters of the Gulf Stream, some coastal areas, particularly in the west of Iceland, provide a relatively mild oceanic climate and apparently ample food stocks to support high survival during most winters. On the other hand, days are very short. For an Oystercatcher that spends December in Reykjavik, the time between sunrise and sunset is just four hours and the average January temperature is -0.6°C. For a bird in Dublin day-length figure is almost twice as long, at seven and a half hours, and temperature is 5.3°C. Food availability may well be compromised by the time available to collect it, as previous studies have shown that feeding efficiency is on average lower at night.

blog of other wadertalesIceland might hold a higher proportion of residents than would otherwise be the case as it is far enough away from Britain (about 750 km to mainland Scotland) and Ireland for the sea crossing to potentially be a significant barrier. For migrants, time will need to be spent acquiring the reserves needed for the journey south in the autumn and north in the spring and the flights may well add costs in terms of survival probability.

There is a blog about the broader project to understand how individual birds become ‘programmed’ to be migrants or residents here: Migratory decisions for Icelandic Oystercatchers.

The migration option 

blog sightingsIf 30% of Oystercatchers are staying in Iceland this implies that up to 26,000 birds of Icelandic origin are to be found in the British Isles and on the western coast of Europe during the winter. Some of these – young birds that are yet to breed – can be found in these areas in the summer too. By the end of the summer of 2017, Verónica Méndez and her team had colour-ringed about 800 (500 adults, 300 juvenile) birds in Iceland, in order to try better to understand the reasons for the migratory/residency decisions that individuals make. Every dot on the map alongside (which was created on 1st June 2018) represents a migratory bird. Each record is valuable and there are lots more birds to try to find! Are there really no Icelandic Oystercatchers in the vast flocks of eastern England?

If you come across a colour-marked Oystercatcher, please report it to icelandwader@gmail.com 

blog bottom

 


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.