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 27^th 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 22^nd 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. You can listen to the programme HERE.

On 27^th 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 small numbers of 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 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 winter frosts.

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.

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

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

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