WaderTales blogs in 2020

Around the world in sixteen blogs

2020 was a strange year, as covid swept around the world and more and more of us faced travel bans. Throughout it all, waders/shorebirds continued to fly thousands of kilometres in spring and autumn.

Five out of sixteen of the year’s WaderTales blogs focused on international migration studies, using a mixture of colour-rings, geolocators and satellite tags. It was particularly interesting to think more about ‘teenage’ waders – the period between fledging and first breeding. It may be a couple of years or more before shorebirds return to their breeding grounds; what do we know about what happens during this period? Are vulnerable and threatened species and the sites that they rely on receiving enough conservation support during these important, teenage years?

• Teenage waders is ostensibly about Hudsonian Godwits that spend the non-breeding season in Chile and breed in Alaska. Juan Navedo & Jorge Ruiz noticed that a small number of satellite-tagged birds headed for Argentina instead of Alaska in April. This led to the discovery of flocks of young Hudsonian Godwits (and adults that choose not to breed in a particular year) in the pampa wetlands – areas that are under threat from industrial-scale farming.
• Spoon-billed Sandpipers: track & trace follows tagged Spoon-billed Sandpipers, as they travel from their breeding sites in Russia, through China and beyond. This is an amazing story; thirteen birds carrying back-mounted transmitters have revealed information that will enable the targeting of conservation measures to support a global population that is estimated to be just 660 birds.
• Gap year for sandpipers is based upon a Peruvian Semipalmated Sandpiper paper that investigates the survival advantage of not migrating north to breed in any particular year. It reveals that taking a gap year may be a sensible strategy in some circumstances.
• Which Icelandic Oystercatchers cross the Atlantic? Around 30% of Oystercatchers remain in Iceland for the winter, with the rest of the population flying south across the Atlantic in autumn. Having made an initial ‘decision’ to be a resident or a migrant, an individual sticks to this strategy but what determines whether a particular Oystercatcher becomes a migrant?
• A Rhapsody of Whimbrel asks whether Whimbrel use time and weather cues in their travel ‘planning’ and whether their plans change during the course of their lives. By looking at weather patterns encountered by tagged birds, flying between western Africa and Iceland, Camilo Carneiro shows that old birds may be able to learn new tricks.

A Scottish trio

2020 seems to be the year of the Scottish WaderTales blog, with three spring/summer stories about research led by RSPB Scotland staff.

• Migration of Scottish Greenshank summarises a study of a small number of breeding birds, using a mixture of colour-ring sightings and geolocator records. Unlike their cousins, that breed in eastern Russia and migrate to Australia or even New Zealand, Greenshank nesting in northern Scotland are short -distance migrants, mostly staying within Britain & Ireland for the whole of their lives
• Trees, predators and breeding waders is all about how the presence of woodland affects the distribution of mammalian predators, even after the trees have gone. Species such as Curlew and Dunlin are benefiting from the removal of forestry plantations from the peat blogs of Forsinard, in north-east Scotland. We discover that it takes a long time for habitat restoration to deliver conservation benefits because of residual levels of predator pressure.
• Scotland’s Dotterel: still hanging on discusses how climate changes are affecting the distribution and numbers of Scottish Dotterel. High up on the Cairngorm plateau, scientists have been studying the links between Dotterel numbers and climate change. The distribution of nests seems to reflect local weather conditions but declining numbers may be more of an African problem.

Nesting waders

• Where to nest? Almost all waders/shorebirds nest on the ground which means that nests are vulnerable to predation. Two main strategies have evolved to minimise egg losses, cryptic egg colouration in open settings and hiding nests in vegetation. A study in Iceland investigates which strategy appears to be more successful and in what circumstances. Do Iceland’s open-nesters (Oystercatcher, Golden Plover & Whimbrel) fare as well as nest-hiders (Redshank, Snipe & Black-tailed Godwit)?
• Curlews and foxes in East Anglia raises some interesting conservation issues. Might it be possible to attract breeding Curlew to patches that can be protected from potential predators? Habitat improvement measures that have been designed to help Stone Curlews are popular with Curlews too. Could shallow soil disturbance be used to support Curlew conservation?

Black-tailed Godwits

WaderTales started out as a way to provide feedback to the volunteers who report colour-ringed Black-tailed Godwits. Most of the twenty blogs about the species refer to islandica but the two in 2020 focus on limosa. The first blog is a follow-up to the 2019 story about a plan to build a new airport within the Tagus Estuary. This threatens to undo much of the good work of Project Godwit – trying to rebuild the English breeding population in the Fens. To raise money for this project, Jen and Mark Smart cycled 1000 km across England, vising many of the sites where head-started Project Godwit chicks have been seen. It was a great opportunity to provide updates on the migration stories of these special birds.

• Black-tailed Godwits are on their way home reveals the importance of the Tagus Estuary (Portugal) to England’s breeding limosa Black-tailed Godwits.
• Cycling for waders is about the head-starting initiative to rebuild the English breeding population of Black-tailed Godwit – and a sponsored cycle ride to support Project Godwit & International Wader Study Group.

Behaviour

Two of this year’s blogs are about bird behaviour, other than migration.

• Disturbed Turnstones focuses upon a paper about the changing distribution of Turnstone in northeast England. As numbers have declined, birds have withdrawn from beaches with more people and dogs. Off-shore roosts seem to have become increasingly important.
• Flagging up potential problems discusses safety issues associated with using flags and flag-mounted geolocators when studying waders. At the heart of the blog is a study of Common Sandpiper survival and migration but there is additional information about ways to minimise problems that may occur when using leg-flags.

Book reviews

Occasionally, the publication of a new book about waders/shorebirds is used as a hook upon which to hang a WaderTales blog. Two new books, Red Sixty Seven and Flight Lines, were treated in this way in 2020.

• Nine red-listed UK waders discusses why nine species of wader find themselves on the UK red list of species of conservation concern). The book, which covers all of the 67 species on the UK Red List, is raising money to help fund scientific research by BTO and RSPB.
• Plovers from the north is a blog about the global migration patterns of Grey Plovers (Black-bellied Plovers). There is an Australian focus but this was a good opportunity to summarise recent research from around the world.

Previous summaries

WaderTales blogs in 2019

WaderTales blogs in 2018

WaderTales blogs in 2017

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.The intention is to add one or two new blogs each month. You can sign up to receive an e-mail notification when a new one is published. There’s a full list of blogs here.

Gap years for sandpipers

Will this Semipalmated Sandpiper fly north to breed?

With the approach of spring in the Northern Hemisphere, waders (shorebirds) that have spent the previous few months on the shores of Africa, the Americas, Asia, Australasia, Europe and oceanic islands need to decide whether to fly north. Those that depart leave behind flocks of young birds, together with adults that ‘choose’ not to migrate north and attempt to breed. In a paper in Movement Ecology, Eveling Tavera and colleagues investigate how the decisions made by individual Semipalmated Sandpipers that spend the non-breeding season in Paracas (Peru) are likely to affect their chances of survival.

Semipalmated Sandpipers

The Semipalmated Sandpiper is one of the smallest of the world’s waders. The species is designated as near-threatened by BirdLife International and IUCN, despite its large breeding range. In their assessment, they draw attention to declining numbers, potentially linked to reduced food supplies in staging areas and to changes to arctic breeding habitat. Hunting pressure in some parts of the wintering range (especially the eastern seaboard of South America and in the Caribbean) may particularly affect Semipalmated Sandpipers that breed in eastern Canada.

Back in the 1970s, when I spent three summers in James Bay (northern Canada), I remember catching skinny juvenile Semipalmated Sandpipers that weighed under 20 g, which is way smaller than a House Sparrow (24.2 g – 30.7 g: BTO BirdFacts). We also caught fat, 40 g  adults that were about to leave and head to countries such as Suriname in South America, perhaps stopping off in the Bay of Fundy on their way south. In just a few months, it would be time to fly north again and I guess we assumed that any bird that was alive would at least try to make the return journey. After all, these are small shorebirds and most small shorebirds breed in their first year.

The distribution of Semipalmated Sandpipers during the non-breeding season covers a broad range of latitudes, from about 25°N (southern Florida) to 23°S (northern Chile and southern Brazil). Some of the birds flying to Arctic Canada, Alaska and Northeast Russia are travelling a lot further than others. A bird setting out on a return journey to northern Quebec from Peru will need to find more resources to fuel its journey than one flying from the Caribbean. The additional fattening requirement could potentially affect the ability of individuals to make the return migration.

Shorebird Survival

Graph from Méndez et al in Ibis

In their global review of annual survival rates of shorebirds, Verónica Méndez and colleagues were able to include 56 species from around the globe. Unsurprisingly, small waders tend not to live as long as larger species. Combining the various studies of Semipalmated Sandpiper, they estimated an annual survival rate for adults of 0.61 (see Measuring shorebird survival). This means that, on average, there’s a 39% chance of an individual dying between one breeding season and the next.

We know that waders don’t always breed every year, as discussed in Teenage Waders. Small waders have lower life expectancy than large waders (Waders are long-lived birds) so missing out on a breeding season makes much more of a difference to a small sandpiper than to a Knot (estimated survival rate 0.8 or 20% chance of dying within the next twelve months) or an Oystercatcher (0.89; 11%).

As Tavera et al point out in the introduction to their paper, although most small shorebirds attempt to breed in their first year of life they may have lower breeding success than older individuals. In Semipalmated Sandpipers, young birds start nesting later in the spring, lay smaller and fewer eggs, and produce fewer chicks (references in paper). When comparing potential reproductive output, a bird that does not migrate north in its first year is probably missing out less than an adult that ‘takes a year off’.

Breeding habitat in Alaska – a long way from Peru

Semipalmated Sandpipers in Peru

The results presented in the Tavera et al Movement Ecology paper come from a long-term Semipalmated Sandpiper colour-ringing study in the Paracas National Reserve, 250 km south of Lima, in Peru. Over a period of five years, 1963 birds were caught in mist nets and individually marked, producing 3229 resightings. Only eight of the marked birds has been seen during the nesting season, all in Alaska and western Canada. This paper builds on a previous paper: Effects of migration distance on life history strategies of Western and Semipalmated sandpipers in Perú.

The key findings in the study are:

• 28% of first-year Semipalmated Sandpipers remain at Paracas, instead of heading north
• 19% of adults remain in Paracas instead of migrating.
• The apparent annual survival rate of first-years that head north is 0.555, compared to 0.671 for first-years that stay at Paracas.
• For adults, apparent annual survival rate of those that migrate is 0.614, compared to 0.808 for those that stay.

The fact that 28% of youngsters in this particular population of Semipalmated Sandpipers don’t migrate north in the first year was unexpected, given what had been learnt from previous studies of the species, but the fact that one in five adults ‘choose’ not to breed in any year is probably more surprising. In a species with a declining population, these missed opportunities to boost the population appear concerning.

Short and long bills

Measuring bill length

Several thousand Semipalmated Sandpipers spend the non-breeding period at Paracas, including individuals with long bills (which are thought to fly there from eastern Arctic breeding populations, about 8,000 km away) and short bills (likely from western Arctic breeding populations, up to 11,000 km distant). There is more about these morphometric differences in this paper by Cheri Gratto-Trevor et al in Waterbirds.

It is not possible to assign individual Semipalmated Sandpipers to a particular population, especially as there are also sex-based differences in bill length, and gender could not be determined in the hand. However, there is a trend for longer-billed birds to be from the east. The eight colour-marked birds from Paracas that have been seen in the western part of the breeding range were all short-billed or intermediate-billed birds.

• Larger-billed juveniles appear more likely to migrate than smaller-billed juveniles, suggesting that Semipalmated Sandpipers that have travelled less far are more likely to breed in the first year.
• Resightings of flagged birds suggest that the survival of first-year birds that fly to the Arctic in their first spring is markedly lower in small-billed birds than in long-billed birds.

The cost of migration seems particularly high in small-billed, first-year Semipalmated Sandpipers. These birds tend to be longer-distance migrants, from the western end of the breeding range.

Modelling the costs and advantages of migration

Eveling Tavera and her colleagues have found that survival is higher for Semipalmated Sandpipers that stay in Paracas than for migrants. During the period April to September, the apparent survival rate for first-year birds and adult birds is much higher for birds that do not migrate.  The survival advantage acquired by non-migrants is significantly greater for adults (0.215) than for yearlings (0.140).

Clutch of Semipalmated Sandpiper eggs

By failing to migrate, individual Semipalmated Sandpipers miss out on a breeding opportunity. Does a bird that lives longer but does not breed in every potential year produce more youngsters than a bird that lives a little less long but breeds every year? In an appendix to the paper, the research team calculate whether the survival advantage for birds that stay in Paracas is high enough, in fitness terms, to compensate for the loss of potential youngsters. They used values for annual survival, mean clutch size and hatching success from studies by Weisser et al and Gratto et al, for adults and first-year birds, to produce figures for Lifetime Reproductive Success (LRS). The predicted survival advantage of non-migrating adults (0.240) is higher than that of first-years (0.134) because they forego a larger average potential reproductive output than do inexperienced birds.

Using these calculations:

Teamwork: birds are mist-netted at night

• On average, a first-year migrant will have the same LRS as a bird that does not migrate if its survival in the first year is no more than 0.134 lower. This is close to the measured value of 0.140 for the Paracas birds.
• On average, an adult migrant will have the same LRS as a bird that does not migrate if its survival in that year of life is no more than 0.240 lower. This is close to the measured value of 0.215 for the Paracas birds.

Based on the modelling of LRS and survival rates, the team conclude that ‘juvenile and adult birds staying at Paracas compensate for the loss of a breeding opportunity with higher survivorship than migrant birds’.

Different non-breeding populations

Tiny bill of an Alaskan Semipalmated Sandpiper

The Semipalmated Sandpipers that breed across North America and the far eastern tip of Russia travel to a wide range of destinations in the autumn, with birds mixing in the non-breeding season. The Paracas site is a long way from the species’ breeding grounds and the results may suggest that migration is constrained by distance. However, there could be other processes at play, especially if food supplies are limited at the time when individuals need to fatten up for migration. Jeroen Reneerkens et al showed that Greenlandic Sanderling that spend the winter near the equator (Mauritania & Ghana) had lower apparent survival rates than birds that travelled much further south (Pretoria). They were also less likely to breed in their first year than birds spending the breeding season in other locations, and arrived on their breeding territories late in the season. Migration distance is not always a problem, it transpires, as long as there are refuelling possibilities on the way north, as described in Travel advice for Sanderling. This is also discussed in Overtaking on Migration, a Black-tailed Godwit blog based upon a paper by Alves et al.

Conservation importance

Much of the statutory protection for migrant waders is based upon sites used in the non-breeding season. Eveling Tavera has shown that Paracas is important for the whole year. Are there other sites that hold 20% or more of their flocks of Semipalmated Sandpipers for the whole year? What are the conservation implications for this species, which is already designated as ‘near-threatened’? Are we doing enough to look after pre-breeding (and non-breeding) flocks? This issue is discussed further in Teenage Waders, built around a Hudsonian Godwit paper by Juan Navedo & Jorge Ruiz.

In conclusion

An individual Semipalmated Sandpiper does not, of course, have the experience or capacity to enable calculation of differential survival rates. The decision to migrate north will be based upon circumstances and the bird’s condition. Effectively, it is trading off the fitness benefit of higher survival against the fitness cost of a foregone breeding opportunity – but it does not know that that is what it is doing. What is interesting, in this study, is that the cost-benefit analysis so closely matches what is found using field data from this particular site. The survival rates and percentage of non-breeding Semipalmated Sandpipers in Suriname or at another site in Peru may well be completely different but could still balance out. There is so much more to learn about shorebird migration.

Oversummering juvenile and adult Semipalmated sandpipers in Perú gain enough survival to compensate for foregone breeding opportunity Eveling A. Tavera, Glenn E. Stauffer , David B. Lank and Ronald C. Ydenberg. Movement Ecology 8,42. https://doi.org/10.1186/s40462-020-00226-6

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