January to June 2022

Here are brief summaries of the first nine WaderTales blogs of 2022. As ever, I am grateful to the authors of the papers that underpin the blogs; they have worked with me to make sure that I get the stories right! I have not covered every new paper; perhaps your favourite is in the pipeline or perhaps I did not happen to spot it? The blogs are described in order of publication.

Welsh Oystercatchers

To explain how flexible Oystercatchers can be in response to changes in their food supply, Katharine Bowgen has brought together long-term data collected by wader ringers and WeBS counters, and added in annual assessments of cockle stocks on the Burry Inlet (South Wales). This paper has a particular resonance, as I remember teaching students about the Burry Inlet Oystercatcher controversy of the 1970s, when complaints from shellfishers led to the deaths of thousands of birds. We understand more about the relationship between shellfish stocks and bird numbers now but what happens when Oystercatchers can’t find food? This paper makes a strong case for the protection of networks of sites, so that individuals have alternatives when needed.

Australian stock-take

One of the great joys of writing WaderTales blogs is that I get to ‘visit’ the flyways of the world without having to burn carbon. How many shorebirds use the East Asian-Australasian Flyway? is a flyway-wide stock-take of the waders that visit Australia and New Zealand, led by Birgita Hansen. It is shocking that a flock of 350 Far-eastern Curlew now constitutes 1% of the global population and that the population of Curlew Sandpipers has halved in double-quick time, but the key strength of the paper is the clear explanation of a methodology that can be used in the future, to monitor changes in numbers.

Chick vocalisation

Big analyses of data sets are very important but it’s lovely when you learn more about the natural history of species that birdwatchers know well. In Australia, Kristal Kostoglou recorded the calls of the chicks of Red-capped Plovers and Southern Masked Lapwings, that were being ringed and measured in the hand. In Chick squeaks I describe how calls get deeper with age, which is not surprising, but that the calls of males and females can become distinguishable from a very early age. Male Red-capped Plover chicks are more demanding than their sisters!

Trans-oceanic migration

There have been several recent wader papers that interpret data obtained from birds when on migration. One of the interesting questions being asked is, “Do shorebirds account for wind displacement continuously or correct for drift later?”. Navigating a vast ocean summarises Jenny Linscott’s work on Hudsonian Godwits, as they cross the Pacific Ocean and then the Gulf of Mexico, on their way from Chile to Alaska. She and her fellow authors show that flocks make continuous adjustments, demonstrating that birds ‘know where they are’ and giving them the ability to fly extremely long distances without running out of energy. There’s some clever maths too!

Hiding in the trees

In the second paper from her PhD, Triin Kaasiku looks at the breeding success of Estonian coastal waders that nest at different distances from woodland. Keep away from the trees describes these ‘edge effects’. In a part of the world where waders are in diminishingly short supply, hatching success is six time as high in open areas as in areas that are within one kilometre of forest edge. The Baltic coast used to be a haven for species such as Curlew and Dunlin but reduced grazing and forestry plantations have provided hiding places for predators. Alongside increased predation, breeding waders are also having to contend with an increasing numbers of nest inundations, arising from summer storms.

Curlew hunting

Curlew hunting stopped in Great Britain in 1982, when the declining wintering population received protection under the new Wildlife & Countryside Act. A fascinating paper by Ian Woodward and BTO colleagues teases apart the positive effects of the cessation of shooting and more benign winter weather. It is summarised as Curlew: after the hunting stopped.

I am old enough to remember when Curlew were hunted in East Anglia. The pâté made from autumn-shot birds is reputed to have been very tasty; I recall Clive Minton getting back in his land-rover and reporting that he had been offered some, when asking for permission to cannon-net Curlew on a Norfolk land-owner’s estate.

Personal appreciation of Whimbrel

On 27 April, Jenny Gill and I were at Eyrarbakki, on the south coast of Iceland. As we watched, small groups of Whimbrel were coming in off the sea. Others were resting on the seaweed-covered rocks, a few were feeding and some flew straight by. Watching waders arrive in Iceland is always magical but, from sightings of satellite-tagged Whimbrel, we could be pretty sure that these tired birds had just completed five-day, direct flights from west Africa. I could not wait to get back to base and to share our observations. It was a good excuse to round up the Whimbrel stories in other WaderTales blogs, as you can read in Whimbrels arrive in Iceland.

Power-line problems

We have seen huge changes in Iceland, since we first visited in 2000, but how are these affecting shorebirds? In the first paper of her PhD (Effects of land conversion in sub-arctic landscapes on densities of ground-nesting birds), Aldís Pálsdóttir investigated how distributions of breeding waders are affected by power-lines. She discovered significantly depressed numbers several hundred metres from the transmission lines, with Whimbrel and Redshank being the most obviously impacted. Her results are written up as Power-lines and breeding waders. With an increasing global reliance on electricity, these are important findings for planners and conservationists.

Conflict with forestry

Just a few days later, Aldís Pálsdóttir’s second paper was published. By mapping distributions of breeding waders in the vicinity of forests, she has shown that new plantations have a massive effect on distributions. In lowland Iceland, the most vulnerable species appear to be Dunlin and Oystercatcher, followed by Whimbrel, Black-tailed Godwit and Golden Plover. It should be noted that three-questers of Europe’s Whimbrel nest in Iceland, as well as half of the Golden Plover and Dunlin. Aldís and her fellow authors argue that Iceland’s waders need a strategic forestry plan. They estimate that recently-planted woodland and forests have already removed the breeding territories of tens of thousands of waders.


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.

Iceland’s waders need a strategic forestry plan

More and more trees are being planted in lowland Iceland – and further increases are planned, in part encouraged by the suggestion that this will mitigate for climate change. Forestry is potentially bad news for Whimbrel, Black-tailed Godwit and other waders that breed in open habitats, and which migrate south to Europe and Africa each autumn. Are there ways to accommodate trees while reducing the damage to internationally important populations of waders?

Pressure on Iceland’s breeding waders

Iceland is changing; more people want second homes in the countryside, the road network is being developed to cope with more and more tourists, new infrastructure is needed to distribute electricity, agriculture is becoming more intensive and there is a push to plant lots more trees. The south of the country is seeing the most rapid loss of open spaces, providing opportunities to study how these incursions affect ground-nesting species, particularly breeding waders.

One of the big changes, especially in Southern Iceland, has been the planting of non-native trees, as shelter belts around fields and country cottages and, more significantly, as commercial crops. Iceland has been largely treeless for hundreds of years but climatic amelioration has facilitated rapid forestry development in areas where tree growth was previously limited by harsher environmental conditions. Seeds of some non-native species are blown on the wind for a kilometre or more, to germinate in open land, well beyond the edge of planned forests.

Most of the new forests are in lowland areas, where we also find the most important habitats for many ground-nesting bird populations. Lodgepole pines may be good news for Goldcrest and Crossbills but not for species such as Golden Plover, Dunlin & Redshank. For breeding waders, the most obvious impact of a new forest is direct loss of breeding habitat but trees can have wider effects, by providing cover for predators and breaking up swathes of open land that are used at different stages of the breeding season. Little is currently known about how predators in Iceland use forest plantations but any perceived risks of predator presence and reduced visibility is likely to influence densities of birds in the surrounding area.

Iceland’s open habitats have suited breeding waders for hundreds of years

Aldís E. Pálsdóttir’s studied changing bird populations in lowland Iceland during her PhD at the University of Iceland, in collaboration with researchers from the University of East Anglia (UK) and the University of Aveiro (Portugal). Among the most concerning of these changes is the rapid expansion of forestry in these open landscapes.

Assessing the potential impacts of trees

In a 2022 paper in the Journal of Applied Ecology, Aldís assesses whether densities of ground-nesting birds are lower in the landscape surrounding plantations and whether these effects vary among plantations with differing characteristics. She and her fellow authors then quantified the potential impact of differing future afforestation scenarios on waders nesting in lowland Iceland.

Forestry currently covers about 2% of Iceland’s land area so the potential for growth is massive. In 2018, the Icelandic government provided additional funding to the Icelandic forest service to increase the number of trees planted, with a goal of enhancing carbon sequestration. As forestry primarily operates through government grants to private landowners, who plant trees within their own land holdings, plantations typically occur as numerous relatively small patches in otherwise open landscapes. These features make Iceland an ideal location in which to quantify the way that plantations affect densities of birds in the surrounding habitats, and to identify afforestation strategies that might reduce impacts on globally important wader populations.

To measure the effects of plantation forests on the abundance and distribution of ground-nesting birds, in particular waders, 161 transect surveys were conducted between May and June 2017. To avoid systematic bias arising from possible “push effects” of corralling birds in front of the surveyor, surveys were conducted along transects that started either at the edge of the plantation, with the observer moving away (79 transects), or started away from the plantation, with the observer walking towards it (82 transects). Please see the paper for the full methodology. The variation in density with distance from plantation was used to estimate the likely changes in bird numbers, resulting from future afforestation plans, and to explore the potential effects of different planting scenarios.

Bird communities change around plantations

Snipe densities are highest close to young forests

On the transects, 3713 individual birds of 30 species were recorded. The nine most common species (excluding gulls, which rarely breed in the focal habitats) were seven waders (Oystercatcher, Golden Plover, Dunlin, Common Snipe, Whimbrel, Black-tailed Godwit & Redshank) and two passerines (Meadow Pipit & Redwing). These species accounted for 88% of all birds recorded.

  • Of the seven waders, Snipe was the only one found in significantly higher numbers closer to plantations. Snipe density declined by approximately 50% between the first (0-50 m) and second (50-100 m) distance intervals, suggesting a highly localised positive effect of plantations on Snipe densities.
  • Densities of Golden Plover, Whimbrel, Oystercatcher, Dunlin and Black-tailed Godwit all increased significantly with increasing distance from plantations. Dunlin and Oystercatcher showed the largest effect (~15% increase per 50 m), followed by Whimbrel (~12%), Black-tailed Godwit (~7%) and Golden plover (~4%).
  • Although Redshank did not show a linear relationship with distance from plantation edges, densities were lowest close to the plantation edge.
  • There were more Redwings close to woodland edges but Meadow Pipit showed no change in density with distance from plantations.

Golden Plover, Whimbrel and Snipe were found in lower densities close to the tallest plantations (over 10 m), when compared to younger plantations (tree height 2m to 5m), suggesting that the impact of forests gets more pronounced as the trees grow. Plantation density and diameter had no additional effect on the species that were in lower densities closer to the plantations, implying that the mere presence of plantations induces the observed changes in abundance. See the paper for more details.

The bigger picture

Aldís Pálsdóttir and Harry Ewing walked every step of every transect and made detailed counts of what they saw – data that are invaluable when considering local impacts of plantations – but the paper becomes even more interesting when the authors look at the bigger picture. When plantations are distributed across these open landscapes, in different configurations, what will be the accumulated effects on the numbers of breeding waders? They estimate likely changes in abundance resulting from planting 1000 ha of plantation in different planting scenarios, ranging from a single block to lots of small patches.

  • Planting 50 smaller patches of 20 ha, instead of 1000 ha of forest in one large patch, is estimated to double the resulting decline in abundance (because there is more forest edge and hence a bigger effect on more open habitat)
  • This effect increases even further as the patches become smaller; in their models, planting 1000 blocks each of 1 ha would have nine times the impact of planting one forest of 1000 ha.
  • Proximity of woodland seems to be the driver of local distributions of breeding waders so the authors suggest that the amount of edge (relative to area) should be minimised, to reduce the impact of a plantation – which means making forests as near circular as possible.

It is clear that fewer larger forestry plots are likely to be less bad than lots of small, local plantations, in terms of the effects on wader populations. The figure below illustrates how much more land is affected when one woodland is replaced by four with the same total area. The grey area (equivalent to a 200 metre annulus) accounts for 88 hectares in the one-patch illustration and 113 hectares for four patches.

An urgent need for action (and inaction!)

Iceland holds large proportions of the global nesting populations of Golden Plover (52%), Whimbrel (40%), Redshank (19%), Dunlin (16%) and Black-tailed godwit (10%) (see Gunnarsson et al 2006) and is home to half or more of Europe’s Dunlin, Golden Plover and Whimbrel. Data in the table alongside have been extracted from Annex 4 of the report, which was discussed at the 12th Standing Committee of AEWA (Agreement on the Conservation of African-Eurasian Migratory Waterbirds) in Jan/Feb 2017.

Aldís measured the areas of 76 plantations in her study, using aerial photographs. The total area of woodland was about 2,800 ha and the total amount of semi-natural habitat in the surrounding 200 m was about 3,600 ha. Using the reduced densities that she found on the transects and the direct losses for the plantations themselves, she estimates potential losses of about 3000 breeding waders, just around these 76 forest plots. Extrapolating this figure to the whole of the Southern Lowlands of Iceland, the total losses resulting from all current plantations are likely to already be in the tens of thousands. Worryingly, the densities measured on the transects in this paper (even 700 m from forest edge) were well below those measured (slightly differently) in previous studies of completely open habitat, suggesting that losses may already be significantly higher than estimated in the paper.

A scary statistic in the paper is that “6.3% of the Icelandic lowlands is currently less than 200 m from forest plantations”. Given the incentives to plant lots more trees, this is particularly worrying for species such as Black-tailed Godwits, the vast majority of which breed in these lowland areas (between sea level and 300 metres).

Non-native trees are spreading beyond the boundary of a planned forest

It has been suggested that breeding waders might move elsewhere when impacted by forestry but migratory wader species are typically highly faithful to breeding sites. If birds are not going to move to accommodate trees, then perhaps plantations should be located where bird numbers are naturally low, such as in sparsely or non-vegetated areas, at higher altitudes and on slopes? Planning decisions could usefully be informed by surveys of breeding birds, to identify high-density areas that should be avoided.

The severe impact that planting forests in open landscapes can have on populations of ground-nesting birds emphasises the need for strategic planning of tree-planting schemes. Given Iceland’s statutory commitments to species protection, as a signatory to AEWA and the Bern Convention on the Conservation of European Wildlife and Natural Habitats, and the huge contribution of Iceland to global migratory bird flyways, these are challenges that must be addressed quickly, before we see population-level impacts throughout the European and West African Flyway.

To learn more

The take-home message from this work is clear. Local planning decisions and the ways in which forestry grants are allocated are producing a patchy distribution of plantations across the lowlands of Iceland, and this is bad news for breeding waders.

The paper at the heart of this blog is:

Subarctic afforestation: effects of forest plantations on ground-nesting birds in lowland Iceland. Aldís E. Pálsdóttir ,Jennifer A. Gill, José A. Alves, Snæbjörn Pálsson, Verónica Méndez, Harry Ewing & Tómas G. Gunnarsson. Journal of Applied Ecology.

Other WaderTales blogs that may be of interest:

Forest edges

Work by Aldís Pálsdóttir (pictured right)

Changing agricultural systems in Iceland (work by Lilja Jóhannesdóttir)


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.

Power-lines and breeding waders

Around the globe, people are consuming more energy, much of which is delivered to cities, towns, individual homes and businesses via over-head electricity cables. In a paper in Ibis, Aldís E Pálsdóttir and colleagues investigate the effects of power-lines on Iceland’s breeding waders. This is the first of several papers from Aldis’ PhD thesis, in which she seeks to understand how forestry and the sprawl of new infrastructures (roads, cottages and power-lines) are changing bird distributions within what were previously open landscapes.

Breeding waders in Iceland

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. In a 2017 report prepared by AEWA (Agreement on the Conservation of African-Eurasian Migratory Waterbirds), in response to concerns about the effects of afforestation on Iceland’s waterbirds, we learn that:

“Iceland is second only to Russia in its importance as a breeding ground for migratory waterbirds in the AEWA region. It supports the most important breeding populations in Europe for six species of waders and is the second most important country for three.”

Data in the table alongside have been extracted from Annex 4 of the report, which was discussed at the 12th Standing Committee of AEWA in Jan/Feb 2017.

Power lines

For waders nesting in Iceland, power-lines are a new addition to a once-open landscape. Pylons provide potential nesting opportunities for Ravens and perches for Gyrfalcons, while the wires between them are a collision risk. Under power-lines, carcases of swans, geese and waders may attract scavenging Arctic Foxes and Ravens, thereby increasing the activities of nest predators. Perhaps these actual and perceived threats affect densities of breeding waders in the vicinity? Or might birds react to something less obvious, such as the emission of UV light or electromagnetic radiation?

In Iceland, the vast majority of electricity is produced from hydropower or geothermal sources, often long distances from the areas in which the power is used. A new move to develop the wind energy sector has the potential to further add to the number of power lines and introduce them in more areas of the country. Much of the increase in electricity production over the last fifty years has been used to fuel industries such as aluminium smelting and there is the potential to further expand generation capacity, perhaps exporting some electricity to other countries.

Much of Iceland’s electricity is used to power aluminium smelters (here, in Hvalfjörður)

Counting the birds

Aldís counting waders on a transect

Aldís conducted the fieldwork for this study between the 6th May and the 20th June 2019, counting birds along 85 transects of between 300 m and 500 m, running perpendicular to power lines. The full methods are described in the paper but it is interesting to see that they included a check to see whether there were different results if walking towards or away from the power lines. Each transect was divided into intervals of 50 m length, each corresponding to 1 hectare of surveyed land. For each power line, Aldís recorded the number of cables, pylon characteristics, and the height and voltage of the line.

Results

In total, 1067 birds of 21 different species were recorded on the 85 transect surveys. Over 90% of sightings were of eight species considered in the subsequent analysis: Dunlin, Black-tailed Godwit, Golden Plover, Meadow Pipit, Redshank, Redwing, Snipe and Whimbrel. Having analysed the data, Aldís and her colleagues concluded that:

  • For all eight species combined, the areas closest to the power lines (0-50 m) supported densities of approximately 112 birds/km2 (±13 SE) which increased by approximately 58% to 177 birds/km2 (±24 SE), in the sector that was between 450-500 m away from the power-lines. On average, there was a 4% increase in abundance between adjacent 50 metre bands.
  • At the species level, Redshank (figure below) and Whimbrel density increased significantly with distance from power lines (18% and 9% per 50 m, respectively) but no other significant effects were detected for other species individually.
  • There were no detectable difference between types of power-lines or relating to the voltages of the electricity they carried.

Implications of the research

In the paper’s discussion there are questions as to why densities of Redshank and Whimbrel (right), in particular, are lower near power-lines. The two species behave differently while nesting, with Redshanks being nest-hiders and Whimbrel nesting in the open, but previous research has shown that their nest predation rates are quite similar (see Where to nest?).

The reason why significant reductions in density close to power lines were apparent for Whimbrels and Redshanks (but not for other species) is not clear but the authors suggest that sample sizes may have been too low for there to have been measurable effects for species such as Dunlin and Golden Plover (below).

Power lines could have direct impacts, such as increased collision risk, but this may be difficult to establish directly, as the authors suggest that carcasses are likely to be quickly removed by scavengers.

Ravens may find it easier to find and predate nests if there are pylons or wires on which to perch but it will be hard to discriminate between an actual predation effect, reducing numbers in areas close to power-lines, and the avoidance of risky areas because of a perceived threat of predation. This is discussed in Mastering Lapwing conservation.

Given the depressed density of ground-nesting bird species in the vicinity of overhead power lines, the authors of the paper suggest that burying power lines might be a better option, even though there would be temporary disturbance to the ground during installation.

What are the implications for Iceland’s breeding waders?

It would be interesting to calculate how many Whimbrel and Redshank (left) territories would be lost over the course of a 50 km run of power-lines through open landscapes – and then extrapolate that to 500 km and 5,000 km. As shown in the earlier table, 75% of Europe’s Whimbrel breed in Iceland. How vulnerable are they to power-line infrastructures and what might be the impact on a breeding population of over 300,000 pairs?

This is the first of several papers from Aldis’ thesis, in which she seeks to understand the current rapid changes to Iceland’s lowland landscapes. Links to other blogs and papers will be added as they appear. It should soon be possible to reveal the combined effects of these incursions into open wader habitats, by considering plans that might affect these areas over the next twenty years, working out potential losses and setting these numbers in a flyway context.

This paper is published as:

Effects of overhead power-lines on the density of ground-nesting birds in open sub-arctic habitats. ALDÍS ERNA PÁLSDÓTTIR, JENNIFER A. GILL, SNÆBJÖRN PÁLSSON, JOSÉ A. ALVES, VERÓNICA MÉNDEZ, BÖÐVAR ÞÓRISSON & TÓMAS G. GUNNARSSON. Ibis. https://doi.org/10.1111/ibi.13089

Here’s a link to another blog about Aldís Pálsdóttir’s research: Iceland’s waders need a strategic forestry plan.

A complementary set of papers by Lilja Jóhannesdóttir investigated how changes to Iceland’s farming may also be affecting breeding waders. These are discussed in three WaderTales blogs:


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.

Whimbrels arrive in Iceland

There is something magical about standing in Eyrarbakki in South Iceland, in spring, watching small flocks of Whimbrel come in over the sea. Thanks to geolocators and satellite tags (about which more later) we know that these amazing waders will have been in the air for around five days, since leaving the west coast of Africa. Looking down at the seaweed-covered rocks on the morning of 27th April 2022, we could pick out small groups of new arrivals. Most were resting but one bird was looking for crabs, just as it had been doing in West Africa just a few days previously. A few birds headed off inland while we were watching, making the distinctive seven-note whistle as they left. It sounded almost like a cry of “made it”!

Incoming Whimbrel: Tómas Gunnarsson

Setting the scene

We had been here before. On 22nd April 2008, I did a live broadcast for the BBC Radio 4 programme World on the Move from this very spot, when I described visible migration to Brett Westwood. On that day, we could see Purple Sandpipers and Turnstone feeding on the tide edge, White Wagtails and Meadow Pipits, newly arrived from Iberia, and small flocks of Golden Plover flying in low over the sea. During the programme, a gaggle of 35 Pink-footed Geese flew in strongly from Britain, as did four Arctic Skuas that had spent winter in the Southern Hemisphere.

On 27th April 2022, the skies were not as busy as they had been fourteen years previously. High pressure over the British Isles and northerly winds across the Atlantic seemed largely to have pressed ‘pause’ on migration from Britain & Ireland. There were newly-arrived White Wagtails, Meadow Pipits and Black-headed Gulls feeding on insects emerging from the banks of rotting seaweed, but the stars were definitely the Whimbrel.

These banks of seaweed will be even more important in May, when there will be hundreds of waders refuelling for the next leg of their journeys, with Sanderling and Dunlin on their way to Greenland and some Knot and Turnstone perhaps flying as far as northeast Canada. When the tide is high enough to wash maggots out of the seaweed, you can sometimes see Red-necked Phalaropes along the tide-line, spinning around and picking food off the surface of the water.

Whimbrel migration

We knew that the Whimbrel were on their way because Global Flyway Network had published a map showing the location of ‘Acuno’, a bird that is wearing a satellite tag that was put on in the Bijagós archipelago of Guinea Bissau. It had been logged west and north of Ireland on the previous evening, already 6000 km and 4 days into its migration. Doing the sums, it seems unlikely that it could have reached Eyrarbakki by the time that we were there but perhaps it flew past soon after, sending signals back to mission control that would confirm arrival**.

** An hour after I published this blog, Acuno was found to have diverted to the Faeroes. It may breed there – as many Whimbrel do – or if could have run out of fuel and landed there, to put on some extra grammes of fat. We’ll see whether it resumes migration.

** Three weeks later, Acuno flew to Iceland. How much will it have been disadvantaged by giving up on direct flight?

Only a minority of Whimbrel fly straight from Africa to Iceland in spring although almost all fly directly south in the late summer. Most individuals spend late April and early May in Ireland, the UK or on the west coast of mainland Europe. Ireland is by far the most important staging area. The individuals on Eyrarbakki beach may have been tired but there could be advantages to being an early bird. See Time to nest again? based on a paper by Morrison et al.

There are several WaderTales blogs about Icelandic Whimbrels:

Whimbrels on the move summarised the movements of Icelandic birds, based on reports of ringed and colour-ringed individuals. In the paper upon which the blog was based (Gunnarsson & Guðmundsson) there was a strong suggestion that birds only stop off in Britain & Ireland on the way north. Geolocator-based research by Alves et al showed that at least some birds were flying straight from Iceland to West Africa and that these sea-crossings could be very rapid.

Migrations to and from Africa were investigated further in a paper by Camilo Carneiro et al that was summarised in Iceland to Africa, non-stop. More recently, papers by the same team have shown that the most consistent point of the annual migration story is departure from Africa and discussed the links between weather and phenology. These two papers have appeared as the WaderTales blogs – Whimbrel: time to leave and A Rhapsody of Whimbrel.

The latest blog about this research is Winter conditions for Whimbrel, based on a paper that assesses the influence of winter conditions on subsequent breeding performance.

Searching for Black-tailed Godwits

We had seen a flock of eight Whimbrel, earlier in the morning, when we were checking fields for colour-ringed Black-tailed Godwits. The Whimbrel were gliding into land, about five km from the coast, before seeming to melt into a patch of rough grassland, bleached after the winter snows.

We did not pay the Whimbrel much attention as, on the other side of the road, there were Black-tailed Godwits probing for worms in silage fields that were already green, after a few days of warmth and the liberal addition of fertilizer. This is our target species during spring trips to Iceland. We have discovered that the arrival time of individuals is remarkably consistent from year to year, which initially seemed surprising, given that migration appears to be getting earlier. There is more about this in Why is spring migration getting earlier? based on a paper in Proceedings of the Royal Society B.

One of the fascinating things about visiting Iceland is that no two years are the same. 2022 has been a dry, warm spring, with northerly winds potentially delaying migration from Britain and Ireland, as mentioned earlier. Early-arriving Black-tailed Godwits that were wearing colour-rings were birds that winter in Portugal and France and migrate via the Netherlands. There was a period of helpful winds for these early birds that fly further but get to Iceland earlier. This strategy is discussed in the blog Overtaking on Migration, based on a paper in Oikos.

Looking forwards

The short Icelandic summer provides fantastic conditions for these waders to raise their chicks, although there are concerns as to how agricultural development, increased forestry and infrastructures will affect these species in the future. In June, in just two months’ time, adults will cross the Atlantic. Black-tailed Godwits head for the British Isles and the west coast of continental Europe and Whimbrel will return to West Africa. By August, the next generation will be preparing for the journey south and we will be here in future springs to monitor their return to Iceland.


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.

Curlew: after the hunting stopped

It is estimated that 120,000 Eurasian Curlew spend the winter in Great Britain, with a further 28,300 on the island of Ireland (Note). Counts made by Wetland Bird Survey (WeBS) volunteers in Great Britain show that the winter population increased following the end of Curlew hunting in 1982 but has since decreased. A paper in Bird Study by Ian Woodward et al investigates how much the temporary recovery was ‘cause and effect’ and asks what other processes may be important, locally and regionally.

Note: Figures from reports in British Birds and Irish Birds, as summarised in the WaderTales blogs, Do populations estimates matter? and Ireland’s wintering waders.

Curlew problems

The 13 species of the Numeniini tribe (curlews, godwits & Upland Sandpiper) are in trouble, with two species probably extinct (as discussed in Why are we losing our large waders?). Eurasian Curlew is red-listed in the UK and described as ‘near-threatened’ internationally.

The wintering Curlew population of Britain and Ireland is made up of birds that move around within these islands and others that breed as far east as Russia. The breeding population of Curlews in the UK declined by 48% over the period 1995-2018, according to Breeding Bird Survey data, but numbers were probably higher still in the preceding period. Trends in other countries are mixed; across Fennoscandia there have been increases in Finland but declines in Sweden, for instance, as discussed in Fennoscandian wader factory.

In the autumn, some UK-breeding Curlew migrate south and west but there are larger arrivals, especially from Finland. Winter numbers on estuaries and wetlands are monitored by WeBS counters, with supplementary information for coastal birds collected periodically (see Waders on the coast). Curlews are site-faithful to wintering sites, so changes in abundance on an estuary will largely depend upon the annual survival of adults that use the site and the recruitment of juveniles.

To survive the winter, a Curlew needs access to sufficient food and to be able to build up fat stores so that it can cope with periods of freezing conditions, when energy loss is high and access to food is limited. In Great Britain, up until 1982 there were additional losses due to hunting. The study led by Ian Woodward aims to establish the local and broadscale factors that might have influenced annual changes in the numbers of Curlew using wintering sites.

Curlew hunting

The estuaries of Britain and Ireland are of huge importance to Europe’s Eurasian Curlew, being significantly warmer than sites in continental Europe on similar latitudes. It is estimated that at least 20% of the European population winters in the British Isles. An adult Curlew is almost as heavy as a Mallard, so it is unsurprising that the species was pursued by hunters, particularly wildfowlers, who encountered them on the foreshore and on wetland sites. When the list of species that could be legally hunted was revised, as part of work to develop the Wildlife & Countryside Act of 1981, Curlew numbers were falling. Shooting of Curlew in Great Britain stopped in 1982 but continued until 2011 in Northern Ireland and 2012 in Ireland.

The national graph from the Wetland Bird Survey (WeBS) can be divided into four sections. There was a rapid decline in wintering numbers during the 1970s, with the UK population reaching a low point in about 1980. Numbers increased rapidly for the next 15 years and then there was a period of relative stability between 1995 and 2000. Since then, the trend has been downwards.

Although not considered in this study (because annual count data are not collected) it is interesting to note that, in the period between 1997/98 and 2015/16, counts of Curlew on open coasts declined more rapidly than on estuarine sites covered by WeBS (40%, compared to 26%). See Waders on the coast.

Looking closely at the WeBS graph, signs of recovery of the UK wintering Curlew population were evident before 1982, when hunting ceased in Great Britain. With numbers falling in the late 1970s, it is possible that hunters chose not to target Curlew, either because they were worried about sustainability or because there were fewer to hunt. Sadly, there is no systematic recording of bag numbers that might help to explain why the upturn in the Curlew graph started before the species received full protection.

Detective work

Ian Woodward and his colleagues started by considering a range of potential drivers of change, other than reduced hunting pressure. Have numbers responded positively to warmer winter temperatures, and might this effect be more obvious in colder regions of the UK? Are there different trends in some estuaries, potentially linked to water quality or the ability to switch to feeding in fields?

The main data available to the BTO team were monthly WeBS counts from north-west England, the Midlands, south-west England, southern England, Anglian region, north-east England and Wales. There was particular focus on 46 estuaries with largely complete datasets and for which comparable environmental data were also available: estuary structure, the presence of coastal grassland feeding areas, potential disturbance and water quality data.

Coastal fields can provide important roosting and feeding areas for Curlew

Why did Curlew numbers change?

The analyses and detailed findings of the study can be found in the full paper in Bird Study. Here are the headlines:

  • When all of the potential drivers of change were considered, the increase in wintering Curlew numbers across the whole of the UK during the 1980s and early 1990s is most likely to have been linked to the cessation of hunting.
  • There has been a redistribution of Curlew over the period of the study, with a higher proportion of a reduced UK wintering population now wintering in the east. Many of the estuaries where numbers have been stable or there have been increases are on the east coast (including the Thames, Blyth, Tees and Alnmouth estuaries). Warmer winter temperatures may have made conditions in the east more suitable for wintering Curlew.
Protracted periods of cold weather are tough for Curlew wintering in the UK
  • Regional trends of wintering numbers were similar across the UK, although the exact timing of the post-hunting peak varied between regions. Numbers are still increasing in north-east England, the coldest region for which data were analysed.
  • In addition to the reduction of direct mortality, Ian Woodward and colleagues suggests that the cessation of hunting may have led to reduced disturbance. Although wildfowlers will still have been shooting ducks and geese, they will not have been directly targeting areas with Curlew flocks.
  • The research team did not detect an effect of changes in water quality, so it is unlikely that the clean-up of estuaries, prompted by the EU Water Framework Directive, had a major effect on the change in Curlew numbers.
  • Curlew numbers decreased during winters with higher numbers of frost days but increased in the following years. An example of the dramatic effect of particularly cold weather was described by a wildfowler, operating on the Wash (Anglian region) in 1991, who came across a small flock of Curlew that had died where they stood, while roosting on the foreshore.
  • In the paper, there is an extensive discussion about the factors that may lead to a redistribution of Curlew, after a period of cold weather. The authors suspect that local redistribution and behaviour changes, rather than long-distance movements, may be the main drivers of changes in annual numbers related to cold weather. Sadly, there is insufficient information to know what factors are at play. How many birds move out of areas to escape freezing conditions but then return to their old wintering areas in subsequent years? Is there a longer-term redistribution of some adults following a cold winter? Do new recruits take advantage of gaps left by missing birds in the winter after a cold-weather event? We need to know more about what happens to individuals in periods of extremely cold weather, which should be increasingly possible now that more Curlews are colour-ringed.

Read more

The analyses presented in the paper suggest that the period of increase, following the cessation of hunting, lasted for around 13 years. Since 1995, declines have resumed. We know that annual survival of the UK-wintering Curlew population is remarkably high, as discussed in another BTO paper by Aonghais Cook et al and described in More Curlew chicks needed. There is very strong evidence that conservation action to support this red-listed species needs to focus upon improving breeding season productivity.

Sadly, the best days for the UK’s wintering Curlew appear to be behind us, with a seemingly relentless decline in numbers since the winter of 1999-2000. This paper could not have been written without WeBS counters and, thanks to them, we will be able to discover what happens next.

The full Bird Study paper is:

Assessing drivers of winter abundance change in Eurasian Curlew Numenius arquata in England and Wales. Woodward, Ian D., Austin, Graham E., Boersch-Supan, Philipp H., Thaxter, Chris B.and Burton, Niall H.K. Bird Study. https://doi.org/10.1080/00063657.2022.2049205


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.

Keep away from the trees

There are concerns that waders nesting in open landscapes are threatened by habitat fragmentation, and may be increasingly so in the future by a drive to plant more trees. Plantations obviously remove nesting space used by species such as Lapwing and Ringed Plover but they could also create hiding places for predators that can then target nests in the vicinity. In a 2022 paper in Animal Conservation, Triin Kaasiku and colleagues report on the outcomes of 753 Estonian wader nests in open areas close to forest edges along Estonia’s coastal fringe. Which are the key predators and where do they hunt?

Wide horizons

Open landscapes have been lost at an unprecedented rate over the past century. Warmer temperatures and reduced management of semi-natural landscapes provide ideal circumstances for the establishment of shrub growth and the expansion of forests. At the same time, afforestation campaigns are encouraging tree planting, to generate revenue and perhaps contribute to climate change mitigations. The combined effects of these drivers are exacerbated by the way that these processes increase the fragmentation of these already-threatened open habitats, which have traditionally provided homes for waders such as Dunlin and Curlew.

The coastal strip that used to provide important breeding habitat has nowadays often become fragmented by forest

Waders in Estonia

The semi-natural wet pastures of the Baltic coast have persisted for centuries, formed by the combined effects of floods, winter ice and postglacial land uplift, and through grazing by domestic livestock and wild geese. Together, these processes have created and preserved important wader breeding habitat. Sixty years ago, Estonia’s coastal grasslands used to be full of Lapwing, Dunlin and Redshank, as well as Black-tailed Godwit, Curlew, Common Snipe and Ruff. Since then, farmland abandonment and afforestation, both as a result of commercial forestry and natural succession, have reduced the area of coastal grasslands by about 70%.

The Boreal Baltic coastal grassland habitat is listed as a priority habitat type in Annex I of the EU Habitats Directive. Despite efforts to restore this habitat, by reducing reed and tree cover over the last two decades, most wader populations in these areas have not recovered. This is discussed in a blog about the effectiveness of agri-environment schemes in the same study area (Remote monitoring of wader habitats). Direct habitat loss is part of the problem for Estonia’s breeding waders but increased predation rates may also be a factor. Triin Kaasiku and colleagues have studied this diverse breeding wader community, to learn more about how nest predation varies across this wet grassland-forest system.

Follow that nest

Wader breeding densities at the study sites varied from 7 to 160 wader pairs per km2; the upper end is considered to be a high density, at the European level. Nests were found and then revisited approximately weekly. The Animal Conservation paper describes fully how evidence was used to determine whether nests were successful and to consider the probable causes of failures. Wader nest survival was measured during three breeding seasons (2018-2020).

Lapwing, Ringed Plover, Redshank and Dunlin were the four main species studied by Triin Kaasiku and her colleagues (see table). They accounted for 655 out of the 753 nests, with six other species providing smaller samples. To understand more about predation events, the team deployed camera traps alongside 85 of the nests, all of which were within 1 km of trees and forests.

Coastal flooding can potentially be a serious issue

About 80% of nesting attempts were unsuccessful (526 out of 655) and the outcomes of 14 other nests could not be established. Of the known failures, 89% were lost to predation, while other causes of nest failures included abandonment (6.7%), flooding (2.3%), trampling (0.2%), and others where the causes were unclear (2.3%). The seemingly high nest abandonment rate may also include some nests that were subject to temporary flooding. The results are based on 679 nests that either hatched or where there was evidence of predation.

There were no discernible differences in survival rates for different species. This is in line with findings in an Icelandic study that compared outcomes of open-nesting species (Golden Plover, Oystercatcher and Whimbrel) with those of species that hide their nests (Redshank, Black-tailed Godwit and Snipe). See Where to nest?

Nest losses

The mean daily survival rate (DSR) for nests was 0.929 which, over a combined incubation and laying period of 27 days, predicts that only about 14% of nests survive through to hatching.

DSR is higher further from the forest and where the amount of cover is lower. These two metrics are obviously related but the effects are teased apart in the paper.

From the modelled data, a nest that is only 20 m from forest edge has a 7% chance of being successful (95% CI = 5-11%), while the equivalent figure for one that is 1  km away is about 26% (18-34%).

Similarly, 3% (1-8%) of nests hatch when local forest cover (within 1 km of the nest) is about 50%, compared to 19% (15-23%) in completely open areas.

Nest success was too low across the whole study area – not enough chicks are produced

Predators and predation

Nest cameras were deployed to track what happened to 85 nesting attempts. Although 64 nests were predated, the camera trap only managed to record the nest predator in 41 cases. Of these events, 31 nests were lost to Red Fox, 5 to Golden Jackal, 3 to Raven and 2 to Badger.

Fox predation occurred on average at 217 m (95% CI=161-273 m) from the forest edge but the other mammals tended to predate nests that were further from cover. Predation events by Raven may also be more frequent closer to forest edge, but these events were rare. Based on the recordings of the camera traps, Red Fox detection rate was higher closer to the forest edge but no similar relationship was found with the proportion of forest cover.

In this Estonian study, wader nest survival did not vary with distance from smaller patches of trees or bushes (<30 m wide). Perhaps these patches may be too small for Red Foxes to hide or forage in.

The bigger picture

There is strong evidence, from studies in the UK and elsewhere, that species that breed in open habitats avoid woodland (see the WaderTales blog Mastering Lapwing conservation) and may experience greater population declines in more fragmented landscapes (as discussed in Curlews can’t wait for a treatment plan).

In the Estonian wet grassland-forestry patchworks studied by Triin Kaasiku and colleagues, Red Fox was the most commonly encountered predator operating close to forest edge. It was in these areas that eggs were most likely to be taken. This is in line with some other studies – but by no means all. The authors discuss in detail why different guilds of predators may have different effects in different circumstances and how patterns might be distorted if waders actively avoid nesting near forests or if there are complex predator-prey networks. See Further Reading below.

Predated Lapwing eggs

Hatching success is not high in any of the areas studied in Estonia – even at the lowest forest cover, only 19% of the nests hatch. This result shows that habitat fragmentation may have more severe effects on the open landscape species than previously realised. It may also indicate that more attention should be directed at the high number of generalist predators.

Conservation implications

In Estonia, as elsewhere, landowners are being encouraged to use land to grow food, to deliver biodiversity gain and to lock up carbon. Others can argue whether planting trees is necessarily a good thing for carbon capture, especially if deep peat is drained and cultivated in the process, but forestry is becoming more fashionable. This paper reminds us that piece-meal planning decisions that, for instance, provide grants to one landowner to preserve habitat for declining species of wader and grants for a neighbour to plant trees, are unlikely to maximise biodiversity benefits.

The full paper is available here:

Predation-mediated edge effects reduce survival of wader nests at a wet grassland-forest edge. Triin Kaasiku, Riinu Rannap and Peep Männil. Animal Conservation. doi.org/10.1111/acv.12774

Further reading

Foxes play leading roles in several WaderTales blogs but this selection may be of particular interest:

Tool-kit for wader conservation looks at different ways of reducing predation, particularly by foxes, within lowland wet grassland. The focus is upon issues in the UK.

Can habitat management rescue Lapwing populations? assesses whether the available tools have the power to deliver sustainable wader populations.

Trees predators and breeding waders is a cautionary tale. Reestablishing nesting habitat for species such as Dunlin and Curlew is not just a matter of removing the trees. It may take up to ten years for predator numbers to drop to levels that are associated with an open landscape.

Dunlin: tales from the Baltic is not focused on predation but fragmentation and predation are parts of the story. Veli-Matti Pakanen’s Finnish research is complementary to the studies in Estonia.


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.

Navigating a vast ocean

The journeys that shorebirds make, as they cross the oceans of the globe, are truly remarkable. Individual birds demonstrate amazing endurance and navigational expertise while in the air for days at a time. Satellite transmitters are providing opportunities to understand how shorebirds refine their flight plans in responses to the wind patterns they encounter. In a paper in Movement Ecology by Jenny Linscott and colleagues, we join the northward flight of Hudsonian Godwits across 7,000 km of the Pacific Ocean and the Gulf of Mexico.

Coping with wind

Conditions encountered en route can dramatically impact the energy that migratory species spend on movement. To complete their journeys across barriers such as oceans, migratory birds need to manage energetic costs by adapting to the wind conditions they encounter. It’s a dynamic environment; no two years are the same and there is often little relationship between local conditions upon departure and what lies ahead, as for instance discussed in the WaderTales blog Rhapsody of Whimbrel.

Migrating Hudsonian Godwits are heading for Alaska

If an individual bird has full knowledge of its location at all times and a fixed destination point in mind, then perhaps it can adjust its airspeed and direction of flight so that it can completely compensate for any lateral drift that is caused by the wind systems en route. Alternatively, it might accept the drift that it experiences or only partly compensate, perhaps gambling that there may be systems ahead that might cause drift in the other direction. It may even over-compensate for the wind patterns it experiences at a particular time, which may be a good idea if there is more of the same weather to come. The authors of the Hudsonian Godwit study explain how these different approaches may integrate to create a movement strategy and summarise what has been found in other studies. Interestingly, it has been suggested that complete compensation (continually adjusting the flight-plan) might not be possible for trans-oceanic flights because there are no landmarks to use as reference points.

Hudsonian Godwits spend the austral summer in coastal Chile and Argentina and migrate northwards in spring, through the midcontinental United States, to breed in subarctic Alaska and Canada. For birds taking off from Chiloé Island in Chile, the first part of the journey takes them across the open Pacific Ocean, the relatively narrow landmass of Central America and the Gulf of Mexico. Godwits making this flight have few or no opportunities to stop, and they traverse several global wind regimes that differ in directionality and strength along the way. The authors predicted that birds would experience drift during their journeys, especially over the featureless open ocean, and increase compensation as they approach North America. Given the vast distances and time spent in flight, it might be expected that the winds experienced during flight should influence the points where individuals cross the coast into North American airspace.

Flock of Hudsonian Godwits on Chiloé Island in Chile – a long way from Alaska

Tracking transoceanic journeys

During the springs of 2019, 2020 and 2021, Jenny Linscott used satellite tracking devices to follow Hudsonian Godwits, as they migrated northward across more than 7,000 km between Chiloé Island, Chile and the northern coast of the Gulf of Mexico.

Prior to migratory departure, two types of solar-powered satellite transmitters were deployed on a total of 54 adults. Technical details are provided in the paper, alongside information as to how the data were filtered and interpreted. This paper focuses on the journey across the Pacific Ocean and the Gulf of Mexico, as birds head towards a relatively narrow refuelling area in North America (the eastern parts of Kansas, Nebraska, South Dakota, and North Dakota).

For any two points along each bird’s route, between Chiloe and the coast of the Gulf of Mexico, it was possible to calculate distance travelled, ground speed, turning angle, and heading. Having removed low-quality data, the team were left with 29 tracks and 689 locations with which to work. They linked each location with the range of possible wind conditions that godwits were likely to be experiencing at the time, depending upon flight height. They then “calculated the total magnitude and mathematical direction of the wind flow for each location at each altitude using vector trigonometry”. Previous studies have shown that migrating waders change altitude in order to find better wind conditions, allowing the team to assign the most likely wind conditions to each godwit location. Please see the paper for details of the modelling and assumption-testing processes.

Results

A total of 24 complete and 5 partial northward journeys were collected from birds migrating north, including repeat tracks from two individuals, which were followed for three years. The sample size was reduced by device failure/malfunctions, presumably some mortality, and by eight birds that oversummered in Argentina (see Teenage Waders and Gap year for sandpipers for information about oversummering shorebirds).  The 25 birds in the study comprised 14 males and 11 females.

  • Godwits for which there were complete tracks undertook continuous flights lasting about six days, covering an average of 8,361 km, before making their first stops.
  • Godwit ground speeds were best predicted by a strategy in which individuals flew at the altitude offering the most wind support in the preferred direction of movement, but were restricted to altitudes at or below 3000 m. It seems likely that the godwits were mostly flying between 100 m and 750 m above sea level.
  • Tracked godwits travelled along paths which showed a close match to a Great Circle line from Chiloé to the North American target area.
  • When flight behaviours were analysed, full compensation was the most frequent behaviour, accounting for 41.1% of all observed flight segments. Fewer segments were associated with partial compensation (23.5%), tail winds (8.1%), full drifting (9.4%), or overcompensation (16.0%).
  • The prevalence of full compensation remained constant across wind conditions. For example, full compensation was the dominant behaviour under crosswinds to the east (32.0%) and west (45.3%). Full compensation was also prevalent across regions, comprising the largest proportion of behaviours exhibited over the Pacific Ocean (45.1%), while crossing Central America (23.9%), and in the Gulf of Mexico (31.4%).
  • There was considerable variation in migration patterns over the Gulf of Mexico and it is suggested that some birds may have been running out of fuel and heading for the nearest land.
  • One individual tracked repeatedly over three years completed its crossing of the Gulf of Mexico in central Texas every year. The other bird tracked for three years had no specific point at which it crossed the coast but always ended up in the same spring staging area.

Jenny Linscott and colleagues found little support for their prediction that godwits would tolerate more drift early in their flight and gradually begin to increase compensation as they approached North America. Instead, both fully supported flight (benefiting from tail winds) and full compensation were common soon after leaving Chiloé. Compensation did not increase with distance travelled, was not constrained during flight over open ocean, and did not influence where an individual ultimately crossed over the northern coast of the Gulf of Mexico, at the end of this flight. Instead, the team found a strong preference for full compensation throughout godwit flight paths. Birds ‘knew’ where they were along their route and could judge how to adjust their headings so as to compensate for the drift they were experiencing at any given time. The paper’s Discussion includes more detailed consideration as to how compensation appeared to operate in different parts of the journey and in different wind conditions.

How do shorebirds, flying over the vastness of an ocean ‘know’ where they are, with no island landmarks? Are individuals within migrating flocks picking up on changes in temperature or humidity, that mark passage through broad wind regimes, can they navigate with reference to sun position and stars, are there magnetic cues, or can they interpret surface swell patterns? Perhaps it’s a mixture of several of these skills? It’s pretty amazing!

Learning more

Jenny Linscott and her colleagues found that fully compensating for wind displacement appears to be a critical strategy for Hudsonian Godwits making a long-distance, transoceanic flight. While godwits often followed wind flow in the early stages of this journey, they nonetheless engaged in full compensation more frequently than any other behaviour during the entirety of the flight, across a vast and apparently featureless ocean. These continuous adjustments help to make sure that birds can fly extremely long distances without running out of energy. The team wonder how well future generations will cope with changing wind systems over warmer seas.

The full paper can be found here:

Compensation for wind drift prevails for a shorebird on a long-distance, transoceanic flight. Jennifer A. Linscott, Juan G. Navedo, Sarah J. Clements, Jason P. Loghry, Jorge Ruiz, Bart M. Ballard, Mitch D. Weegman, and Nathan R. Senner. Movement Ecologyhttps://doi.org/10.1186/s40462-022-00310-z

The Hudsonian Godwits studied here are flying 7,000 km north across the Pacific, but this pales into insignificance when compared to Bar-tailed Godwits that commute between Alaska and New Zealand. The Pacific was once considered a barrier to migration but it is increasingly seen as a conveyor belt. There is an excellent review article by Theunis Piersma and colleagues in Ornithology, the title of which explains its content:

The Pacific as the world’s greatest theater of bird migration: Extreme flights spark questions about physiological capabilities, behavior, and the evolution of migratory pathways. Theunis Piersma, Robert E Gill, Jr, Daniel R Ruthrauff, Christopher G Guglielmo, Jesse R Conklin and Colleen M Handel. Ornithology,  https://doi.org/10.1093/ornithology/ukab086


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.

Chick squeaks

During the first few weeks of life, wader chicks rely upon their parents to take them to good feeding spots and to look out for potential predators. These youngsters will need to come when called and to freeze or hide when a crow flies over or a fox is on the prowl. A wader chick communicates with its parents too, so that they know where it is and can be alert to distress, but are there more subtle messages being communicated and why do male and female chicks produce discernibly different calls?

Kristal Kostoglou has been listening to the chicks of Red-capped Plovers and Southern Masked Lapwings in Australia and analysing recordings of their calls. Her research is presented in a 2022 paper in Ibis.

Handling waders

Broken-wing distraction display by parent Red-capped Plover

Anyone who studies breeding waders will be aware that parents get very anxious if a chick that is being ringed and measured starts making alarm calls – but how many people have recorded those calls? As Kristal Kostoglou says in the abstract of the paper she has written with her coauthors “We opportunistically recorded calls of chicks while they were in the hand and analysed the calls to determine whether call structure is related to sex or body mass (a proxy for age)”. The results are fascinating.

At the start of the paper, there’s a useful summary of previous studies of the calls made by chicks. It is believed that developmental changes in chick vocalisations can allow parents to assess chick age and/or condition, with evidence that calls get deeper (frequency drops) as chicks get larger. There have been a couple of previous wader studies, relating to Pied Avocet and Eurasian Stone-curlew. In the Ibis paper, Kristal Kostoglou investigated potential relationships of call traits to body mass and sex in chicks of two shorebird species; Red-capped Plover and Southern Masked Lapwing.

The two study populations

The calls of Red-capped Plover chicks were recorded in the Cheetham Wetlands (Victoria, Australia) and the Southern Masked Lapwings were studied on Phillip Island (Victoria, Australia). Parents brood and defend their chicks which fledge at about 35 days (plovers) and 45 days (lapwings) respectively. Nests were found during incubation and most chicks were ringed just after hatching. Each chick was measured & weighed, a recording was made, and a small amount of blood was taken, to establish sex.

Recording the sounds made by a Red-capped Plover chick, as it is weighed and measured

Sound recordings were made using a portable digital recorder and an omnidirectional microphone. The 26 plover chicks made between 1 and 248 calls each and the 95 lapwing chicks produced between 1 and 336 calls. Data were collected from 9 female plovers and 17 males, between from the day of hatching and approximately 4 weeks of age. For lapwings the equivalent figures were 46 females, 49 males and up to 5 weeks of age.

Six call traits were analysed: call duration, the time between calls, entropy, minimum dominant frequency (kHz); dominant frequency range (the difference between a call’s minimum and maximum dominant frequency); and frequency modulation. Please see the Ibis paper for more details and technical information about the analyses. This related paper may also be of interest: Anatomy of avian distress calls: structure, variation, and complexity in two species of shorebird.

Results

For Red-capped Plovers:

  • Males were more vocal – time between calls was shorter for males than for females.
  • Heavier (and hence older) chicks called more frequently.
  • As mass increased, the dominant frequency range of calls decreased (calls became less shrill).

For Southern Masked Lapwings:

  • For both sexes, dominant frequency range decreased with increasing body mass (calls became less shrill with age).
  • The decline in dominant frequency range was greater in males, resulting in a lower dominant frequency range than for females. This meant that the difference between the calls of the two sexes became more discernible over time.
  • Frequency modulation was lower for males than for females.
  • As body mass increased, frequency modulation and entropy of lapwing calls decreased.

In the Discussion, the authors consider how a heavier bill and changes to the structure of the upper vocal tract might be linked to the results. It has been suggested that chicks modify sound output to utter more adult-like calls, as they get older.

Red-capped Plover chick

A faster repetition rate of distress calling, as observed in Red-capped Plovers, might encourage parents to provide more defensive support for male chicks, which could contribute to the higher survival of male over female chicks, as reported for several plover species.

For Southern Masked Lapwings, there appeared to be sex-linked differences in calls from hatching, with these differences getting more marked with age. This could mean that either the voice anatomy develops differently or that vocal control is different in male and female chicks.

Conservation implications

Southern Masked Lapwing chicks, at the point of hatching

Both Red-capped Plovers and Southern Masked Lapwings are considered to be of ‘least concern’, according to the IUCN/BirdLife conservation criteria. Many other waders, around the globe, are under various levels of threat, with predator pressure being a significant cause of decline for some species. The ability of adults and chicks to stay together through to the fledging of the chicks could be particularly important, in these cases, with communication being key to success.

Kristal Kostoglou’s study analysed distress calls, which she and others suggest may be under the influence of natural selection. She points out that some non-distress vocalisations, such as contact calls, might communicate further information about the caller’s sex. It is also possible that distress calls may serve to communicate with siblings or with other chicks, not just with parents. In the paper, the authors suggest that future studies could investigate associations between shorebird chick calls and sex, using the full repertoire of chick calls and across species whose adult call repertoires and characteristics vary between sexes. There were few recaptures of chicks in this study and the authors suggests that it would be interesting to observe how calls of individually-marked chicks change over time.

A passing thought

Head-started Black-tailed Godwit chicks have no contact with their parents

One issue that might be considered by others is how chick calls develop if there are no parents in attendance, as we see if chicks are head-started. There is a growing movement to support populations of threatened wader species by removing first clutches of eggs, incubating them and then rearing the chicks in captivity. In their pens, they have no contact with adults and communicate only with each other.

It is clear that head-starting has worked for Spoon-billed Sandpipers, a species that was heading for extinction as discussed here, and the early signs are good for England’s breeding Black-tailed Godwits but do these hand-reared individuals miss out in some ways? Potentially the ‘language’ developed within the family may be important when the chicks are themselves parents? That’s not going to be easy to test! However, perhaps it might be possible to see if there are any differences in the development of calls between hand-reared and parent-reared chicks of the same species?

Communication between parents and chicks helps to keep the family together

In summary

The study published in Ibis provides the first evidence for charadriid chicks of (a) a sex difference in call structure and rate and (b) gradual growth-related changes in call structure and rate, across chicks. The detailed write-up will hopefully be useful in further studies of shorebird vocalisations during growth, which may help further to explain the development and functional significance of all that squeaking!

Vocal traits of shorebird chicks are related to body mass and sex. Kristal N. Kostoglou, Edward H. Miller, Michael A. Weston and David R. Wilson. Ibis. https://doi.org/10.1111/ibi.13055

Red-capped Plover chick seeks to hide in the cracked mud, using the shadow to break up its outline

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.

Who eats African Oystercatcher eggs?

As ornithologists, focused as we are upon birds, we perhaps find it hard to fully acknowledge birds’ eggs as key ‘consumables’ in the food web – a ready source of protein for everything from snakes to deer.

Nest cameras have shown that clutches of ground-nesting waders are taken opportunistically, by grazing sheep for instance, but there are also some species – or individuals – that are specialist egg hunters. See Prickly problems for breeding waders (hedgehogs) and Curlews and foxes in East Anglia (sheep).

In their paper in Wader Study, Itxaso Quintana, Rio Button & Les Underhill describe a single-year study of the predation of African Oystercatcher nests on Robben Island, best known for the prison where Nelson Mandela was held for eighteen years, and for its important seabird colonies. Introductions and eradications on Robben Island have created a far-from-natural food-web that is ever-changing. The situation that Itxaso, Rio and Les found in the 2019/20 breeding season included Kelp Gulls ‘protecting’ African Oystercatcher nests from the attentions of Mole Snakes – something that makes little sense unless set in a historical context, as the authors do in their paper.

What a mess!

Homo sapiens has interfered spectacularly on Robben Island, in the same way as in so many other places, with exploitation of seals, the introduction of an array of large mammal species from the mainland during the apartheid era, and the introduction of rabbits, fallow deer and cats. By 2019/20, the rabbits and almost all of the deer had been removed, encouraging the regeneration of ground cover, and over 90% of the cats had been culled. The remaining threats for African Oystercatcher nests were expected to come mostly from Kelp Gulls, native Mole Snakes and the small number of remaining cats.

Checking out an Oystercatcher’s nest on the shoreline

The 550 African Oystercatchers on Robben Island account for 8% of the species’ population, making this a very important breeding site. This total comprises both nesting pairs and non-breeding birds. African Oystercatchers do not migrate, relying on local shellfish supplies year-round. In 2000, the species was classified as ‘near threatened’ but, thanks to the spread of the invasive Mediterranean Mussel along the South African coast, numbers have recovered. Native shellfish might be in trouble but at least the African Oystercatcher can now be considered to be of ‘least concern’!

The 2019-20 breeding season

Robben island has a coastline which is less than 10 km in length, enabling the authors to monitor 158 nesting attempts of what is thought to have been 133 pairs of African Oystercatchers. A further 300 non-breeding oystercatchers were also present. There were three main study sections, corresponding to the north end of the island (63 nests), the south end of the island (64 nests) and the east side (29 nests). The nest success rates of nests in the north and south were very different, with rates in the east being intermediate.

Below the gull colony in the north of the island, 45 out of 63 African Oystercatcher nests were successful (71%) with one failure associated with Mole Snakes.

Away from the gull colony, in the south of the island, only 14 out of 64 African Oystercatcher nests were successful (22%) with 17 failures associated with Mole Snakes and the reason for most failures unknown.

Breeding Kelp Gulls are spreading across the northern part of Robben Island

There was far more evidence of Mole Snake activity in the south of the island, as can be seen in the map, with individual snakes seemingly ‘patrolling the shoreline just above the spring high tide level, where African Oystercatchers lay their eggs’. In the north, where African Oystercatchers nest on the shoreline immediately below the Kelp Gull colony, snakes were much less conspicuous. You can read more about this in the paper.

Two decades of research

The long-term study of African Oystercatchers on Robben Island started in 2001. Since then, the population has increased fourfold and the number of nests has almost doubled. There have been many changes over this period, as you can read in the paper, but the most significant one for African Oystercatchers is the arrival of Mediterranean Mussels, first noticed in South African waters in 1979 and already colonising the shoreline of Robben Island by 2003. These invasive mussels provide more food than native shellfish and the authors suggest that this has fed through into higher oystercatcher nesting densities.

The beak of an African Penguin is enough to deter Mole Snakes

Over the two decades, there has been a massive change in the populations of potential predators. In the early part of the research period, Mole Snakes were considered relatively unimportant, in terms of predation pressure on African Oystercatchers. Introduced cats, however, then became a major problem, with numbers growing between 2001 and 2005, to such an extent that at least 83% of African Oystercatcher nests were predated in the 2004/05 breeding season. Culls in 2005 and 2006, followed by continued controls, have lowered cat numbers to fewer than ten individuals.

There were no Kelp Gulls breeding on Robben Island until 2000/01, when the first five nests were found. More and more birds now make the short commute to Cape Town, to scavenge, and 2829 gull nests were recorded in 2019/20. Like other large Larus gulls, Kelp Gulls have a reputation as egg thieves. However, on Robben Island, where there are few people disturbing nesting African Oystercatchers, and forcing them to leave their nests, the gulls seem to cause few problems. Instead of being a threat, Kelp Gulls attack Mole Snakes, thereby protecting the eggs of the African Oystercatchers.

For Kelp Gulls, it’s only a short commute to Cape Town, where they scavenge for food

Four other species have benefited from reduced cat numbers. As hoped, numbers of Hartlaub’s Gulls and Swift Terns have both increased, while Mole Snakes have experienced higher survival because the eggs of these two species are available in the austral autumn and winter. African Penguins have benefited too, as a consequence of reduced cat predation, and their sharp beaks can deal with Mole Snakes.

What next?

Hatched Oystercatcher chick and another one on the way

The current situation seems to suit all of the species considered here. Removing introduced herbivores has provided more suitable habitat for snakes, and nesting numbers of key seabirds and African Oystercatchers have all increased since most cats were culled.

Robben Island is not a natural ecological system, however. Major perturbations have happened over decades, with introductions, extirpations, culls and the arrival of invasive species. For the moment. the authors see no reason for Kelp Gulls and/or Mole Snakes to be controlled, in order to support African Oystercatcher numbers or protect important seabird populations.

Cold searching the area above the tide-line to locate nests of African Oystercatchers (Mole Snakes do the same)

One thing that seems almost certain is that the situation will change again: the local Mediterranean Mussel population could collapse, for example due to disease; a pollution incident in the busy sea lanes into the port of Cape Town could suddenly impact birds and/or their food supplies; the grinding effects of climate change, particularly the risk of increased storminess, could slowly upset the equilibrium; diseases such as avian influenza, currently affecting Cape Cormorants, could spread further; or the cat population could explode again. Robben Island looks like a fascinating place in which to study complicated predator-prey interactions; here’s hoping that long-term monitoring will continue.

Paper

The full paper is available in Wader Study, the journal of the International Wader Study Group.

African Oystercatchers on Robben Island, South Africa: The 2019/2020 breeding season in its two decadal context.
Itxaso Quintana, Rio Button & Les G. Underhill. Wader Study.


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.

New Bar-tailed Godwit Subspecies

The description of a new subspecies of Bar-tailed Godwit begs two questions, ‘How do we identify new subspecies?’ and ‘Is the concept of a subspecies helpful?’. Put simply, the answers are ‘That depends’ and ‘Yes, especially when subspecies are the focus for conservation action’.

A new study of Bar-tailed Godwits, and the proposal to identify Limosa lapponica yamalensis as a new race, usefully highlight the importance of the flyway between Siberia and the Arabian Sea and the challenges being faced by waders that use this migration route.

Limosa lapponica yamalensis

Bar-tailed Godwits breed across the whole of northern Eurasia and in Alaska. Since the last Ice Age, following glacial retreat, new breeding opportunities in northern latitudes have become available to waders. The emergence of separate migration flyways, linking wintering and breeding areas, has led to a divergence of the species into a number of distinct populations, some of which have already been defined as subspecies. In their paper in IBIS, Roeland Bom (NIOZ Royal Netherlands Institute for Sea Research) and colleagues from the Global Flyway Network argue that the taymyrensis subspecies should be further divided between those that winter in the Middle East (and presumably East and South Africa) and those that winter in West Africa. Their recommendation is based on studies of migratory behaviour, breeding area, morphology (measurements) and population genetic differentation in mitochondrial DNA. Their main focus has been a study of spatial and temporal differences in migration routes.

How many subspecies?

The most famous subspecies of Bar-tailed Godwit is baueri; these amazing birds fly directly from Alaska to New Zealand at the end of the breeding season and return via the Yellow Sea in spring. Theirs is the most impressive migration route of any wader, including non-stop flights of well over a week. These are the largest Bar-tailed Godwits.

Bar-tailed Godwits wintering in Australia are mainly birds of the menzbieri race. These breed from central Siberia across to north-east Russia and migrate north and south via the Asian coast, especially the Yellow Sea. Bar-tailed Godwits breeding further south in eastern Russia are usually described as anadyrensis, these birds are smaller than baueri but bigger than menzbieri.

Bar-tailed Godwits breeding in western Siberia have all been known as taymyrensis, named after the Taymyr** Peninsula, while those breeding in Scandinavia, Finland and the far west of Russia are identified as lapponica. Nominate Limosa lapponica lapponica birds winter in northwest Europe and most taymyrensis use the East Atlantic Flyway to winter at least as far south as Guinea-Bissau in West Africa. Taymyrensis is the smallest race. Lapponica and taymyrensis were recognised as separate subspecies two decades ago and this differentiation has been useful in discussions about Bar-tailed Godwit conservation. In the UK we see both lapponica and taymyrensis, as discussed in Bar-tailed Godwits: migration and survival.

Until now, birds migrating south from western Siberia, as far as East and South Africa, have been considered to be taymyrensis and it is these birds that have been reclassified – with the new name of yamalensis, after the region of Russia in which the subspecies breeds.

** In the IBIS paper, the authors use Taimyr (rather than Taymyr) as this is preferred by Russian co-authors. I am maintaining consistency within WaderTales.

What’s different?

The studies summarised in the IBIS paper by Bom et al are designed to test whether Pavel Tomkovich, who has studied Russia’s artic-breeding waders for several decades, was right when he suggested that taymyrensis should be split into two subspecies. (See Population structure and migratory links of Bar-tailed Godwits: Current knowledge and unsolved issues in Achievements in Studies on Waders of Northern Eurasia). Based on a small number of movements of ringed birds between areas where there are few birdwatchers, Pavel suggested that L. l. taymyrensis likely comprises two distinct (flyway) populations, one wintering in the Middle East, West Asia and East Africa and breeding on the northern West-Siberian Plain, and the other wintering in West Africa and breeding on and around the Taymyr Peninsula.

Using satellite-tracking, Roeland Bom and colleagues have now described the migration routes, breeding destinations, and annual-cycle timing of Bar-tailed Godwits using wintering areas in the Middle East (Oman) and West Africa (Mauritania and Guinea-Bissau). To understand further the extent to which the two groups are different and whether or not there is any mixing of the two populations, they also examined differences in mitochondrial DNA.

Tracking through space and time

Members of the research team attached solar-powered tags to eastern taymyrensis Bar-tailed Godwits in Oman and western birds in Mauritania, Guinea-Bissau and the Wadden Sea. 52 birds caught between 2015 and 2018 provided usable tracks; 11 birds (12 tracks) linked the western wintering/migration route to the area in and around the Taymyr peninsula, while 9 birds (19 tracks) linked the Middle East to the northern part of the West Siberian plain. To limit potential negative effects of carrying extra weight, only the largest birds were tagged, which means that all of the tags were deployed on females.

Bar-tailed Godwits from wintering areas in the Middle East staged for several days in the areas around the Caspian and Aral Seas, during both northward and southward migration. Both of these areas were already thought to be important for passage waders but analysis of tracking data emphasise the critical role they play in the annual cycle of Bar-tailed Godwits. Some birds also spent short periods of time at sites in the United Arabian Emirates, Iran and India. After leaving their breeding sites, some birds moved up to 1,000 km north, to feed in high-Arctic coastal Siberia, before embarking on southward migration.

Bar-tailed Godwits tracked from wintering sites in West Africa staged in the Wadden Sea, during both northward and southward migration, with other staging points in Spain, Portugal and France, during northward migration. From the Wadden Sea, most West Africa birds flew directly to the northern West-Siberian Plain (near or in the breeding area of the Middle East birds) before heading for the Taymyr Peninsula. All birds routinely moved north before leaving for the Wadden Sea, with many using the same fuelling areas as Middle East birds.

Although birds from West Africa and the Middle East used the same feeding areas in spring and post-breeding, the phenology of the two populations were different. The northward migration, the arrival in the staging and breeding sites and the southward migration of Middle East birds were earlier than for the West Africa birds. Some birds of the two groups could be found in the same areas in Siberia in the pre- and post-breeding staging, emphasising the fact that timing differences can be just as important as spatial separation when it comes to the evolution of subspecies. This ‘spatial overlap but with timing differences’ story is similar to that seen in limosa and islandica Black-tailed Godwits in The UK and The Netherlands, as discussed in Godwits in, godwits out: springtime on the Washes.

Body size and shape

The measurements of taymyrensis and yamalensis overlap but there is a tendency for Middle East birds to have smaller bills and longer wings than West African birds. The authors suggest that, given that the two subspecies have similar diets during the non-breeding season, the different bill structure may be related to feeding requirements during the breeding season, with taymyrensis breeding in open tundra and yamalensis breeding in forest tundra and bogs within the boreal zone. It is interesting to note that the morphological differences between the taymyrensis and yamalensis subspecies are greater than those between taymyrensis and lapponica.

Genetics

West African and Middle East birds could not be separated using genetic tools available to the researchers. The authors point out that there is very little genetic variation between the three more western subspecies (lapponica, yamalensis and taymyrensis), indicating that either these three populations may have diverged recently (i.e. well after the last Ice Age) or that there is still some (small) geneflow between subspecies. The authors dicusss this in depth, in the context of all known populations of Bar-tailed Godwits and of waders in general.

A new subspecies

Roeland Bom and colleagues conclude that the old taymyrensis taxon consists of two distinct populations with mostly non-overlapping flyways, which warrant treatment as separate taxonomic units. They argue that ‘separation in space and time’ can define separate subspecies and that these differences will become apparent before morphological (size and shape) differences develop and long before it will be possible to spot genetic differences.

Breeding locations of tagged Bar-tailed Godwits

Yamalensis Bar-tailed Godwits breed on the northern West-Siberian Plain including the Yamal Peninsula. Birds of the subspecies follow the Central Asian Flyway, with main stopover sites in the Caspian Sea and the Aral Sea. Satellite tracking has connected Oman with other wintering areas in the Middle East, Iran, Pakistan and West India. It is likely that some birds continue further south on the West Asian – East African Flyway, with two, earlier ring recoveries showing that the subspecies can winter as far south as South Africa.

Conservation considerations

One of the key benefits of defining yamalensis as a new subspecies is that priority setting (and hence funding) for conservation action is often defined at the subspecies level. As we learnt from Ashwin Wisvanathan and Les Underhill at the International Wader Study Group conference in 2021, the numbers of waders spending the non-breeding season at the southern extremes of the Central Asian Flyway (in India) and of the West Asian – East African Flyway (in South Africa) have declined alarmingly over the last few years.

Roeland Bom and colleagues quote population estimates for taymyrensis and yamalensis Bar-tailed Godwits of 600,000 and 100,000-150,000 respectively but these are old numbers and West African winter populations are known to be declining. It is important to establish new population estimates and trends for the two populations and better to understand the migration of yamalensis. Potentially, more satellite tracking might help to suggest where to look for wintering yamalensis along the vast coastline from the southern tip of Africa to the southern tip of India, and to identify further spring and autumn stop-over sites.

Paper

The paper in IBIS concludes with a detailed description of the subspecies Limosa lapponica yamalensis, together with measurements that separate it from other races. You can read more in:

Central-West Siberian-breeding Bar-tailed Godwits (Limosa lapponica) segregate in two morphologically distinct flyway populations. Roeland A. Bom, Jesse R. Conklin, Yvonne I. Verkuil, José A. Alves, Jimmy de Fouw, Anne Dekinga, Chris J. Hassell, Raymond H.G. Klaassen, Andy Y. Kwarteng, Eldar Rakhimberdiev, Afonso Rocha, Job ten Horn, T. Lee Tibbitts, Pavel S. Tomkovich, Reginald Victor & Theunis Piersma. IBIS.

Other WaderTales blogs about waders on the West Asian – East African flyway

Well-travelled Ring Plovers makes a link between North Africa and the furthest northeast corner of Russia, extending the reach of the West Asian – East African Flyway further east than sometimes shown on maps.

In search of Steppe Whimbrel describes the migration of Numenius phaeopus alboaxilliaris, a Whimbrel subspecies that has already been declared extinct once. The subspecies migrates between the steppes of Kazakhstan and Russia and coastal East Africa.

Following Sociable Lapwings describes the migration of this threatened species along both the West Asian – East African Flyway and the Central Asian Flyway, with some interesting thoughts about a migratory divide in a wader which exhibits relatively low philopatry.


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.