Trees, predators and breeding waders

When trees are planted in open habitats that support breeding waders, numbers usually decline pretty quickly. Trees not only directly remove once-occupied habitat, they are also thought to attract predators, by providing somewhere to hide. In their paper in Restoration Ecology, Mark Hancock and colleagues investigate the distribution of thousands of scats of mammalian predators, in order to understand predator activity in landscapes associated with open bogs and forest edge. They were particularly interested in seeing how long it takes for predators to move out of an area when trees are removed and the land once more reverts to blanket bog.

This study took place alongside a project to repair damage to the vast Flow Country blanket bog (northern Scotland), that occurred in the 1980s, when non-native conifer trees were planted in areas of deep peat that had been drained and deep-ploughed. Such forestry practises would nowadays be prohibited.

More trees

The spread of trees can occur naturally, as the northern treeline moves further north or as trees grow higher in mountain regions, or it can be imposed or accelerated when trees are planted in previously open environments. Warmer temperatures create more opportunities for afforestation and politicians seem to be responding to rising CO₂ levels by opting for what seems like an easy win – ‘let’s plant more trees’. In the right places, using appropriate native species, woodland can help to capture carbon**, support woodland wildlife and provide multiple other benefits to society. However, if afforestation focuses on open wet landscapes it can potentially threaten ground-nesting wader species such as Dunlin and Curlew.

** link to The value of habitats of conservation importance to climate change mitigation in the UK by Rob Field and colleagues in Biological Conservation.

As Mark Hancock and colleagues indicate in the abstract of their paper, afforestation of formerly open landscapes can potentially influence mammalian predator communities, with impacts on prey species like ground-nesting birds. In Scotland’s Flow Country, a globally important peatland containing many forestry plantations, earlier studies found reduced densities of breeding waders on open bogs where forestry plantations were present within 700 m. See Hancock et al. 2009 and Wilson et al. 2014. A previous WaderTales blog discussed whether apparent avoidance is due to actual or perceived predation risk (See Mastering Lapwing conservation) but whichever it is, adding new woodland to open wetland habitats has the potential to affect sensitive breeding waders.

Fox scat

There have been many studies looking at the effects of trees on breeding waders but the key differences in this case were that researchers monitored how mammal distributions changed as woodland was removed, in an effort to restore biodiversity and valuable blanket-bog habitats. Spoiler alert: it takes several years to reduce predator numbers!

By counting scats of species as diverse as fox and hedgehog the team were able to address three questions:

• Did scat distributions vary between open bog, forestry plantations, and former plantations being restored as bog (‘restoration’ habitats)?
• How fast did scat numbers change in restoration habitats?
• Were scat numbers different in bogs with differing amounts of nearby forestry?

Counting the poo

Forestry transect

The analyses in this paper are based upon surveying 819 km of track verges, which yielded a total of 2806 scat groups (groups of scats that could have come from one animal) from a variety of predators. I smile when days and days of painstaking fieldwork are summarised in a sentence. “We measured summer scat density and size over 14 years, in 26 transects 0.6-4.5 km in length, collecting data during 93, 96 and 79 transect-years in bog, forestry and restoration habitats respectively”. There is no mention of midges either!

The Flow Country is host to a range of predatory mammals. Hedgehog, Wildcat, Red Fox, Badger, Pine Marten, Stoat and Weasel are native species, while introduced species like Feral Ferret and American Mink may be threatening the area. A 10 mm diameter scat could have been produced by one of six or more species – and increasingly it has been shown that genetic methods, which were outside the budget of this study, are needed to properly identify species from a scat. As all of these species prey on the eggs and/or chicks of breeding waders, the study treated them as a ‘guild’ of animals having similar potential effects.

In April each year, fieldworkers – many of them volunteers based at RSPB’s Forsinard Flows reserve – walked along each of the transects, removing all of the scats from the tracks and track-edges. In July, scats and scat groups that had been deposited on the tracks during the breeding season were counted, measured and their positions recorded using GPS (see paper for details).

Nine transects were in open bog habitat, that remained broadly unchanged throughout the study, 8 were in forestry plantations, 8 were in forestry plantations that were cleared and then restored during the study and 1 site was already a restored plot. For ‘restoration’ transects, the number of years since felling was used as a measure of the length of time under restoration management. In these restoration areas, the brash that was left after felling gradually rotted away or became buried by recovering bog vegetation as re-wetting management (e.g. drain blocking) took effect.

Where’s the poo?

Transect through bog

Predator activity in different habitats and over time. For bog and restoration habitats, scat group density was relatively low throughout the study, averaging around 1 to 2 scat groups per km. In forestry transects, scat group densities started at similar values, but rose approximately eight-fold over the study period, as the forests matured. In the final year of the study, scat group densities in forestry averaged around eight groups per km – approximately twice the figures in restoration and six times the figure in bog habitats. There is a suggestion that more mature forests may have suited Pine Martens, in particular: this species was recorded in the heart of the Flow Country for the first time during the study period.

Trees removed – restoration transect

Predator activity once trees are removed.  Scat group density differed significantly between restoration areas of different age classes. In recently-felled sites (1-5 years), densities were about 2.4 groups per km, rising to 4.0 in the middle period (6-10) and falling to 1.3 later (11-14 years). The authors suggest that tree removal may lead to a flush of nutrients, grasses and then small mammals, thereby explaining the increase in scat densities during the middle stage (6-10 years). The paper demonstrates that it takes several years for mammal densities to fall back to ‘natural’ levels, after tree removal.

Pine Martens have moved into the area

Predator activity close to forests. Scat density on open bog transects was significantly affected by the presence of at least 10% forestry cover within 700 m. There was an estimated 2.9 times (95% confidence limits 1.4 to 6.0) higher scat density at bog transects which contained over 10% cover of forestry within 700 m, compared to bog transects with less forestry nearby. Scottish studies of breeding waders have shown that species such as Golden Plover, Dunlin and Curlew avoid areas close to forestry and the paper includes references to several other similar studies elsewhere.

The Conservation picture

As pointed out by Hancock et al in their Discussion, scat densities in forestry reached much higher values than those of open bogs, especially as the plantations matured, implying that afforestation had strongly altered patterns of mammalian predator occurrence in this formerly open landscape. It took ten years of restoration management to drive down scat densities to levels similar to those of open bogs but, as the authors note, peatland restoration is a rapidly developing field and newer techniques may allow faster restoration, with both biodiversity and soil carbon benefits.

These findings have implications way beyond the scope of this study, three examples of which are included below:

Commercial forestry is seen by some as a way of capturing carbon and can provide opportunities to restore our woodlands, especially our native woodlands and their associated biodiversity. However, given the vulnerability of ground-nesting birds to predation, and the potential for afforestation to markedly affect predator communities, care needs to be exercised when considering afforestation of open landscapes.

Warmer climates offer opportunities to add forestry to the mix of land use options in areas in which the growing season used to be considered too short. For instance, there is significant development pressure in Iceland to plant large areas of non-native commercial forestry. Given that the country holds half or more of Europe’s breeding Whimbrel, Dunlin and Golden Plover this is a contentious issue. This AEWA report is important: Possible impact of Icelandic forestry policy on migratory waterbirds.

In Ireland, it has been suggested that a patchy distribution of relatively new forestry plantations may be one of the factors contributing to the drastic decline of Curlew numbers. (Ireland’s Curlew crisis describes a 96% decline in just 30 years). It has been proposed that some of these patches should be removed. The Hancock et al paper shows how long it might take to make a difference – ten years may simply be too long for Ireland’s breeding Curlew.

Read more

The paper that forms the basis of this blog is:

Guild-level responses by mammalian predators to afforestation and subsequent restoration in a formerly treeless peatland landscape by Mark H. Hancock, Daniela Klein and Neil R. Cowie. Published in Restoration Ecology. https://onlinelibrary.wiley.com/doi/abs/10.1111/rec.13167

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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

Plovers from the north

Despite its global distribution, the Grey Plover (or Black-bellied Plover in the Americas) does not get the attention it deserves, according to Andrew Darby, author of Flight Lines, a book about shorebird migration and Grey Plovers in particular.

Who would want to study a shorebird that is the first species to sneak away from its tundra nest when danger threatens, and that is hard to catch outside the breeding season? Fortunately, satellite technology means that a lot can be discovered by following just a small number of birds and this blog will focus on two individuals, setting their travels within a broader flyway context.

Flight Lines

Grey Plovers CYA and CYB are the stars of Flight Lines, a book by Andrew Darby which takes us ‘across the globe on a journey with the astonishing ultramarathon birds’. They were caught together in Adelaide’s Gulf St Vincent by members of Victoria Wader Study Group on 14 November, 2015. Here, they were carefully fitted with tags that were originally to be deployed on Bar-tailed Godwits. So starts a story that takes us from the south coast of Australia to islands off the north coast of eastern Siberia, via the Yellow Sea.

Andrew has not simply written a bird book; Flight Lines tells the sort of tale that I remember from school days, of how Cook and Magellan travelled the globe or Livingstone and Stanley ‘discovered’ Africa. Grey Plovers have been flying to the Arctic for millennia – from Europe, Africa, Asia, Australasia, the USA and South America. CYA and CYB are doing what their ancestors have always done. As we follow their journeys, Andrew tells us about the habitats these birds need, shares stories about the lives of local people who await their arrival, reveals the way that shoreline ‘development’ is impacting upon their survival and tells us about some of the ornithologists who are  encouraging governments and local communities to save space for the birds with black wing-pits (see picture below).

Territoriality

Grey Plovers travel vast distances across the globe but once they have arrived at their final destinations they are highly territorial – and not just in the breeding season. When David Townshend studied marked individual Grey Plovers feeding on the Tees, in north-east England, back in the late 1970s, he discovered that they fed in the same places for the four-month period of the winter, defending their patches against interlopers; what’s more, they returned to these territories in subsequent years. It’s like running a marathon and then not leaving your back yard until it’s time to take off again, months later.

As Andrew Darby reminds us, Grey Plover can re-visit the same territories for decades; something to remember when considering what happens when a coastal development steals the ‘homes’ of all of the Grey Plovers in a bay. How does a twenty-year old bird find a new home? There’s a WaderTales blog about longevity records for waders/shorebirds.

Territoriality is not just a British thing. In Flight Lines we learn that the same is true for American Black-bellied Plovers wintering in San Diego and Grey Plovers in South Africa’s Eastern Cape. Here, tracking has shown that the patterns that David Townshend witnessed by day are maintained during the night. Those big eyes can make the most of low light-levels. A hungry individual stands still and waits for prey to move, gives up after a while and tries another likely patch within its territory. Plovers are not like Knot; they don’t have a sensitive tip to the bill that can detect hidden prey, their hard-tipped bills grab items from the surface of the mud or sand, guided by those big, black eyes.

Global distribution

According to BirdLife International, the global population of Grey Plover is only about half a million birds, 80,000 of which use the East Asian-Australasian Flyway. This system of aerial ‘motorways’ links countries as diverse as New Zealand and Thailand with breeding areas in the East Russian Arctic and Alaska.

There is a temptation to sit at home and think of migration as something that happens in a line that runs north to south and back again. Fifty years ago there was an assumption that Black-bellied Plovers would migrate north and south within the Americas, that Grey Plovers in western Europe and Africa would be linked to western Siberia, that Australian birds bred in eastern Siberia, and that Grey Plovers in southern Africa, the Arabian peninsula, India etc  would be birds that had flown from ‘the middle bit’ – between western and eastern Siberia.

Studies of other shorebirds have shown more cross-overs than might have been expected, breaking up the neat south-north pattern. Chukotka, for instance, indicated by the red star on the BirdLife map, is a summer home for Ringed Plover from Egypt (Well-travelled Ringed Plovers), Spoon-billed Sandpipers from Bangladesh, Knot from Australia and Buff-breasted Sandpipers from South America.

Shorebird mixing happens on the other side of the Bering Sea too. Shorebirds that fly to Alaska from South America in spring are joined by Bar-tailed Godwit that fly north from New Zealand, via the East Asian coast. These baueri race Bar-tailed Godwits are famous migrants – they fly non-stop all the way to New Zealand come fall/autumn. See paper by Phil Battley et al.

So, what about Australian Grey Plovers? Do they meet up with American Black-bellied Plovers?

Linking wintering and breeding areas

As Andrew Darby tells us in Flight Lines, measurements of Grey Plovers in Australia and in Russian breeding areas suggested that wader experts Clive Minton and Pavel Tomkovich were handling the same birds in Victoria and on Wrangel island, north of the Russian mainland. In 2007, Pavel banded some Grey Plovers, the hope being that one of them might be seen in Australia. The only one of these Grey Plovers ever to be reported was seen in the Chinese part of the Yellow Sea – six years later.

The Grey Plover colour-ringed by Pavel was spotted by David Melville, who has done a great deal to fill gaps in knowledge about the vast flocks of waders that use the Yellow Sea, including significant numbers of passage Grey Plover. One of the wonderful features of Flight Lines is the way that it turns names into characters. I had heard of many of the people who Andrew met or spoke to, during research for the book, but I appreciate their roles much better now. There is fantastic work taking place in countries throughout the Flyway, ably coordinated through the East Asian-Australasian Flyway Partnership.

Given that colour-ringed Grey Plovers were not providing the data that could link breeding and wintering grounds, it was time to try something new. On 14 November, 2015, CYA and CYB were fitted with satellite transmitters and in March they flew north. In the same way that we read that Captain Cook ‘discovered’ Australia, without telling the story of the challenges his crew faced on the way, I am just going to present the map of the northward journeys of the two birds and leave you to read Flight Lines, the log-book of their journeys.

The map shows the positions on 7 June 2016, when CYA and CYB had only just arrived on Wrangel Island. The journey north is described by Tony Flaherty in Victoria Wader Study Group Bulletin number 39.

“The two satellite transmitters, put on to Grey Plover in South Australia by Maureen Christie’s team in November, 2015, have performed brilliantly, with both birds successfully migrating northwards, including a long stop-over in the Yellow Sea, and eventually going on to breed on Wrangel Island off the north coast of Chukotka, eastern Siberia. This is the first evidence of any bird from Australia visiting this remote Arctic Island. At the time of writing this, both are now on their way back from the Arctic, with one having made a surprising major detour via the New Siberian Islands.”

There is a complementary article about the journey south in the next issue of the VWSG Bulletin, also by Tony Flaherty.

Map data courtesy of Victorian Wader Study Group & Friends of Shorebirds SE. The project was made possible by support from the Australian Government and the Adelaide and Mt Lofty Ranges Natural Resources Management Board.

A conservation agenda

One of the major drivers of bird ringers/banders is a thirst for knowledge – and there is nothing wrong with that spirit of enquiry. For the East Asian-Australasian Flyway there is a deeper imperative; conservation of birds using habitats that are under immediate threat from human exploitation and climate change. A previous WaderTales blog – Wader declines in the shrinking Yellow Sea – focuses on a paper that highlighted the desperate need to understand and conserve shorebird populations. One species that hardly gets a mention in that paper is the Grey Plover. It’s not that there is no threat to Grey Plovers, it’s just that there were insufficient data. It’s not easy to study these territorial plovers, which are thinly spread throughout the non-breeding range and difficult to catch.             

About Flight Lines

The WaderTales blog series started out as a planned book about Black-tailed Godwits but I found that I did not have the stamina to weave together science tales into an interesting tapestry. Andrew Darby is a master of the writing craft. Although he focuses upon waders, and the Grey Plover lead characters, he also tells us about the pioneer ornithologists who have explored the East Asian-Australasian Flyway, in search of shorebirds that spend Christmas and New Year in Australia and New Zealand. Flight Lines is published by Allen & Unwin. ISBN 978 1 76029 655 1

Migration research about other Grey Plover populations

Papers about Grey Plover and Black-bellied Plover are thin on the ground but new projects on the East Atlantic Flyway and in the Americas are starting to fill in some of the gaps in our knowledge.

The Wash Wader Ringing Group has ringed/ banded over 6500 individual Grey Plovers since the Group was founded in 1958 (Sixty years of Wash waders). Their work was written up in 1976 by Nick Branson and Clive Minton (Moult, measurements and migrations of the Grey Plover). The map alongside shows movements of birds to and from the Wash.

Recent research by Klaus-Michael Exo and colleagues has used satellite tracking to understand better the movements of Grey Plover breeding in the Taimyr and Yamal regions of Siberia. In their paper, they identify important staging sites as well as wintering areas between Ireland and Guinea Bissau. Tagged birds stopped off for long periods during migration, especially in late summer and autumn. See Migration routes and strategies of Grey Plovers on the East Atlantic Flyway as revealed by satellite tracking.

The Tidal Wings project focuses on Grey Plovers that winter in the Bijagos archipelago of Guinea Bissau. You can keep up to date on their discoveries on their website (https://birdecology.wixsite.com/tidalwings) and on Twitter. The map above shows three migrations of the same individual.

In North and South America, the Black-bellied Plover is also receiving increased attention. There is a large collaborative project to reveal their migratory connectivity, with over 70 tags deployed to track birds from Alaskan and Canadian breeding grounds, and from Texas and Louisiana wintering grounds. Work is being conducted by the Smithsonian’s Migratory Connectivity Project, USGS Alaska Science Center, Environment Canada, Texas A&M University, University of Missouri, Brighman Young University-Hawaii, and Coastal Bend Bays and Estuaries Program. The map alongside was provided by Autumn-Lynn Harrison of the Smithsonian Migratory Bird Center and shows example migration routes from one breeding population in Nome, Alaska. 

Colour-ring studies. Satellite tags are a key part of modern wader and shorebird studies, providing immediate insights from just a small number of birds, but simple bits of plastic can play a role too, especially in Western Europe, where lots of birdwatchers visit coastal sites. Colour-ring studies in East Anglia and northwest England are revealing more about how Grey Plovers use a suite of different estuaries during the course of the non-breeding seasons and will ultimately monitor annual survival rates. It will be interesting to learn whether individual birds hold territories in each of the estuaries that they visit, to moult, spend the winter and prepare for spring migration. The importance of allocating individual leg-flags to ringed birds is discussed in Bar-tailed Godwit: migration & survival.

I look forward to seeing more papers about the Grey and Black-bellied Plover, the shorebird that breeds at the top of the world.

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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

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.

• Results from bird ringing suggested that return migration in spring from West Africa to Iceland often involves stop-overs in Ireland or Britain, as well as on the Atlantic coast of mainland Europe. See Whimbrels on the move and the paper Migration and non-breeding distribution of Icelandic Whimbrels.
• This pattern was confirmed using geolocators. The autumn journey south is nearly always direct but 80% of flights from West Africa to Iceland involve stop-overs. See Iceland to Africa non-stop and the paper Faster migration in autumn than spring.
• By looking at repeat tracks for the same individuals, it became possible to investigate the timing of events during a Whimbrel’s annual calendar. The most obvious fixed point in the year was departure time from West Africa in the spring. See Whimbrel: time to leave and the paper Why are Whimbrel not advancing their arrival dates into Iceland?

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.

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:

• Potentially, arriving in breeding areas early may confer advantages which can be explained by the ability to nest again if a first attempt fails. See Time to nest again? based on the paper Why do earlier-arriving migratory birds have better breeding success?
• The timing of migration is driven by new generations, rather than by individuals changing what they do. See Generational Change based upon Mechanisms driving phenological change in migratory species.
• Birds can make up for the ‘disadvantage’ of flying further south if they make an early spring movement to a staging area closer to their breeding grounds. See Overtaking on migration and the similarly titled paper.
• Once birds are locked into a particular pattern of migratory timings they stick with them – they don’t know that there are better options. See Travel advice for Sanderling based upon Low fitness at low latitudes.

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!

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.

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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