Sixty years of Wash waders

wwrg tt balance

Weighing a Turnstone

The Wash Wader Ringing Group (WWRG) started with a bang on 18 August 1959, when the team made a catch of 1,132 birds in a Wildfowl Trust rocket-net at Terrington, in Norfolk. Over the years, cannon have replaced rockets, catches have become generally smaller and the scientific priorities have been refined, but the Group continues to focus upon discovering more about the waders that use the Wash. This blog attempts to summarises what has been learnt about the waders that rely upon the Wash, the vast muddy estuary that lies between Lincolnshire and Norfolk, on the east coast of England.

Sixty years ago, the first goal was to understand where the vast flocks of waders that visit the Wash came from – a task that would provide great insights into the way that the whole East Atlantic Flyway works. In this time, over 300,000 birds have been caught and ringed on the Wash, as you can see in the table below. Equally importantly, hundreds of bird-ringers from across the UK and scores of visitors from around the world have joined WWRG teams, in order to learn more about the study of shorebirds. Further international collaboration has been fostered through overseas visits by WWRG members and emigration of some key personnel. The impact of the Group is truly global, as you can read in the WWRG report for 2014/2015.

wwrg table

A total of 307,226 birds is impressive, especially when some of the species totals are compared to the national totals of the BTO Ringing Scheme for the whole of Britain & Ireland since 1909. WWRG is responsible for over 40% of the Grey Plover, Knot, Sanderling and Bar-tailed Godwit, with Grey Plover topping the list at nearly 60%. These are terrific achievements for a group of volunteers. I don’t have the figures but I reckon that Nigel Clark has been responsible for the largest number of catches.

Wee quiz: What’s the best match between these Wash waders and the countries that they are quite likely to have come from? Answers at the end of the blog:

  • Species: Bar-tailed Godwit, Black-tailed Godwit, Curlew, Oystercatcher, Sanderling, Turnstone
  • Countries: Canada, Greenland, Iceland, Norway, Finland & Russia
wwrg box

Firing box connected to 4 cannon-nets

In the early days, rocket nets were borrowed from the Wildfowl Trust for an annual summer week of catches, but the development of cannon-nets gave opportunities for all-year ringing. The intensity of the Group’s activities grew in the 1970s, when there was a threat to build a freshwater reservoir on the mudflats. For a couple of years, Clive Minton (founder and leader) persuaded us to visit fortnightly, so that we could get better data on weight-gain and turn-over, using a mixture of cannon-netting and mist-netting. Everything we knew was published by the Group as The Wash Feasibility Study in 1975. These days, the Group gets together about ten times a year for catching and colour-ring-reading sessions.

wwrg oldies

By catching and ringing large numbers of the key species that visit the Wash, the Group was able to generate maps showing what are now well-known patterns of migration (see Which wader, when and why?). Early on in the Group’s history, there was a focus on nine species, with Black-tailed Godwit added as a tenth when numbers increased. Each of these species has its own section below. The maps were prepared for the Wash Wader Ringing Group 2016/2017 Report by Ryan Burrell, using data stored within the BTO archives. Blue dots represent WWRG-ringed birds that have been found abroad. Red triangles represent foreign-ringed birds caught on the Wash. The base maps used are by courtesy of Natural Earth (www.naturalearthdata.com).

Oystercatcher

wwrg map OCThe map alongside clearly demonstrates the strong link between the Wash and Norway. Other interesting things that have been discovered about Oystercatchers:

  • They live a long time. An Oystercatcher that we caught at Friskney on 30 July 1976 broke the longevity record for a BTO-ringed wader when it was shot in France on 4 April 2017 (41 years 1 month and 5 days). It was ringed as an adult so we don’t know the exact age – but it must have been at least 43 years old. There’s a WaderTales blog with a list of longevity records for BTO-ringed waders.
  • When life gets tough, Oystercatchers fail to complete their autumn moult, retaining some of their outer primaries for an extra year. The ability to complete moult and annual survival rates are both affected by cockle and mussel supplies on the Wash. There’s more about this in two papers in Biological Conservation and the Journal of Applied Ecology.

Grey Plover

wwrg GV GVIn the early days of the WWRG, Grey Plovers occurred in much smaller numbers than they do now. Writing in an article about the first 40 years of the Group, Clive Minton told the story of the first catch of 100, made in 1963, that was celebrated with three bottles of champagne provided by the late Hugh Boyd, delivering on an incentive that he had promised.

  • Over half of the Grey Plover that have been ringed in Britain & Ireland since 1909 have been ringed by WWRG since 1959 (58.9%)
  • All of the Grey Plover using the Wash breed in Siberia. Some birds spend the winter on the Wash but there are autumn moulting flocks of birds that will go on to winter in other parts of Britain & Ireland, and spring and autumn passage of birds that travel as far south as West Africa.
  • Grey Plover are late to leave the Wash, with the last departures not occurring until the start of June. Unsurprisingly, they are some of the last waders to return at the end of summer, which puts pressure on birds to finish moult before the short, cold days of winter. Some adults fail to complete primary moult, especially if food supplies are low. There is more about Grey Plover moult in this WaderTales blog.

wwrg map GV KN

Knot

wash knot

First-winter Knot (subterminal bands on wing coverts and, as yet, unmoulted juvenile fethers on upper-parts)

Knot (or Red Knot) are truly international waders, as is shown in this map of movements of islandica  (and a few canutus) birds  to and from the Wash. Several WWRG members have been heavily involved in efforts to understand the decline in numbers of the rufa subspecies in Delaware Bay (on the North American eastern seaboard) and Clive Minton has been at the heart of efforts to explain the sudden drop in survival of piersmai and rogersi adults that winter in Australia and migrate to Arctic Russia via the Yellow Sea (see Wader declines in the shrinking Yellow Sea).

  • We are still learning about Knot migration. The cluster of reports of WWRG-ringed birds in Northern Norway looks odd on this map projection but it turns out that this is a well-used stopping-off point for islandica Knot heading for northern Greenland and NE Canada. This route was first confirmed in 1985, when a joint Durham University and Tromsø University expedition caught 18 Wash-ringed birds in a total catch of 1703 birds.
  • wwrg net set

    Setting cannon-nets

    Many birdwatchers visit the Wash in autumn and winter to see the swirling Knot flocks at Snettisham and Holme. If high tide is at first light, Knot and other waders sometimes roost on Heacham Beach, giving the occasional opportunity to make a significant catch. The most recent of these, on 11 February in 2012, included 2757 Knot, 77 of which were already wearing rings.

  • The most recent analysis of wader populations in Great Britain showed that there was a drop of nearly 20% in wintering Knot numbers (from 320k to 260k) in less than a decade (see Do population estimates matter?). Regular catches on the Wash will help produce estimates of annual survival rates and age ratios of the islandica subspecies.

Sanderling

wwrg sanderlingThe biggest catches of Sanderling are generally in the summer, when the Wash is a meeting point for birds from Greenland and Siberia. July can sometimes see catches of 200 or more birds. Traditionally, a Sanderling catch was the curtain-raiser at the start of Wash Week, an opportunity for the whole team to make one catch before splitting into ‘Terrington’ and ‘Lincolnshire’ teams for the rest of the main summer trip.

  • Wintering Sanderling on the Wash are thought to be exclusively of the race that heads northwest in the spring, to Greenland via Iceland.
  • Late summer and spring see the addition of birds passing through on their way from/to Siberian and Greenlandic breeding areas.
  • I well remember the first time we caught a Sanderling (on 26 July 1975) wearing an Italian ring (caught in Italy 9 May 1975). Thanks to Jeroen Reneerkens (whose work will be covered in an upcoming blog) I now understand that this is probably a bird that migrates from Namibia to Greenland in spring, via the Mediterranean. It will have been on its way back to Namibia when caught in July.

wwrg map SS DN

Dunlin

wash dunlin

Sam Franks, looking for the buffy tips on inner coverts, which distinguish first-year birds from adults

Nearly half of the waders caught by WWRG have been Dunlin – a total of 140,168 up until the end of 2018. There were really big flocks of Dunlin in the 1970s but numbers have dropped over the years, with peak counts now half what they were, according to WeBS data.

  • We caught over 3,500 Dunlin in one week in 1976 but the annual total has exceeded 1,000 in only four of the last ten years. Partly, this reflects a change in behaviour in the summertime, with fewer waders roosting on fields and hence less catchable.
  • Three races of Dunlin visit the UK. Our winter birds are alpina, from Siberia, NW Russia and northern Scandinavia. A lot of July birds are schinzii, breeding in the UK and as far north as Greenland, and we occasionally try to convince ourselves that we have caught an arctica from northern Greenland.
  • Data collected for the WeBS survey suggest that national winter totals have dropped by over 40% in 25 years. This could perhaps partly be explained by a redistribution of alpina, with new generations of young birds settling in wintering areas on the other side of the North Sea. Warmer winters may well make this a more practical proposition than in the 1970s. There’s more about this in this paper.

Black-tailed Godwit

wash blackwit

Newly ringed Black-tailed Godwit, caught in a mist-net at night.

Black-tailed Godwits became a priority species in 1995, when Jennifer Gill (University of East Anglia) started a project to study the movements of individuals, using colour-rings. Nearly 25 years later, the WWRG-ringed Black-tailed Godwits have contributed data to numerous papers, largely focusing upon migration.

  • The Wash is a hugely important area for moulting islandica Black-tailed Godwits. Some birds stay in East Anglia for the winter but others move south and west within the UK, west to Ireland and south to France, Portugal and Spain.
  • There are several blogs about Black-tailed Godwits in this WaderTales contents list.

Bar-tailed Godwit

One of the key things that was learned from the sudden decline in annual survival rates in a range of species that use the Yellow Sea (as mentioned above) is a need for regular monitoring of marked birds. The WWRG’s Scientific Committee set up colour-flagging projects for Bar-tailed Godwit, Curlew and Grey Plover, in order to increase the reliability of estimates of annual survival for three species that the Group does not catch in sufficient numbers to generate good retrap histories. Birdwatchers can help by reporting colour-marked birds here.

wwrg barwit map etc

  • In Bar-tailed Godwits: Migration & Survival there is a comparison of the data generated by a catch of 505 Bar-tailed Godwits in 1976 with the information that has been generated recently, using colour-flags.
  • Bar-tailed Godwits are long-lived birds. A WWRG bird holds the current record for a BTO-ringed Bar-tailed Godwit: 33 years and 11 months between ringing in 1978 and recapture in 2008. BTO longevity records are discussed in this WaderTales blog.
  • Colour-ring reading is now a significant element of Group activities, as described by Rob Pell in the WWRG Report for 2016/2017.

Curlew

Back in the 1970s, Curlew were still hunted on the Wash (paté made from autumn-shot birds was reported to be very tasty). Shooting stopped in Great Britain in 1981, when the maximum winter count on the Wash had dropped to about 3,000 birds, and by 2003/04 the maximum winter count was 15,336. Since then, numbers have declined, in line with national and international trends.

wwrg curlew map etc

  • A large number of Curlew on the Wash in winter are from Finland and surrounding countries. Surprisingly few are of UK origin.
  • Birds wearing WWRG leg-flags have been observed breeding in the Brecks (Norfolk/Suffolk).
  • The Curlew is internationally designated as ‘Near Threatened’. Is this really true when we can still see a field with 1000 roosting Curlew in Norfolk? Answers here.

Redshank

wash redshThe latest population estimates suggest that Great Britain has lost 26,000 wintering Redshank in less than a decade, representing a drop of 20%. Perhaps WWRG data can be used to help to explain these declines? Here are some of the things we know:

  • The Redshank on The Wash in the winter are mainly a mixture of birds from around the Wash, across the UK and from Iceland.
  • In cold winters, Redshank wintering on the Wash die in large numbers. After a period of severe weather in 1991, nearly 3,000 wader corpses were collected from along the tide-line, about 50% of which were Redshank. The winter WeBS counts for Redshank dropped by 50% after this mortality event but have recovered somewhat since then.
  • An analysis of nearly 1,000 dead Redshank showed that about two-thirds were of Icelandic origin. There was a tendency for smaller birds to be more susceptible to cold weather mortality than larger birds of the same species (More information in this paper by Jacquie Clark)

wwrg map RK TT

Turnstone

wash ttWinter Turnstone are birds that will head for Greenland and NE Canada in the spring but recoveries of birds in Finland and other Scandinavian countries indicate a passage of continental birds. African recoveries of WWRG-ringed birds probably include birds from Canada/Greenland and Finland/Scandinavia.

  • Turnstone wearing US Fish & Wildlife Service rings are occasionally caught on the Wash. Some of these rings were put on by Guy Morrison and his colleagues in Alert, Ellesmere Island, Canada. Guy was an early member of WWRG. It’s a small world!
  • The first Wash Turnstone were colour-ringed in 1999, as part of a study to understand why birds were feeding on the docks at Sutton Bridge. There is a WaderTales blog about the resulting paper by Jen Smart and Jennifer Gill. Colour-ringing continues, to measure annual survival rates.
  • Turnstone have a reputation for eating almost anything (including dog excrement and a human corpse) so do not be surprised if you see a colour-ringed bird scavenging for chips on the Hunstanton sea-front.

A few more highlights

Ringed Plover: this is not one of the ten key study species but 1,432 have been ringed between 1959 and 2018. Some birds are local breeders that hardly move anywhere but other birds link the Wash with Greenland, northern Norway, Morocco and Senegal.

wwrg GKGreenshank: The Group supports a colour-ringing project that was initiated by Pete Potts, in Hampshire. More information here.

Spotted Redshank: During the period 1959 to 2018, WWRG ringed a total of 85 Spotted Redshank, representing over 20% of the total ringed in Britain and Ireland since 1909. Amazingly, sixty of these birds were ringed on the same day – 27 July 1975. There is a blog about this catch and the recent decline in the number of Spotted Redshank visiting the UK. Fewer Spotted Redshanks.

Ruff: Until its closure, WWRG members spent many a smelly night at Wisbech Sewage Farm. This was a great place to catch Ruff, Curlew Sandpipers, Green Sandpipers etc. in mist-nets. Group members wrote a paper about Ruff moult and migration.

Rares: Occasionally there are surprises! WWRG has caught one each of Stone Curlew, Pectoral Sandpiper, Broad-billed Sandpiper and Terek Sandpiper. The last bird features in this WWRG blog.

What do we know now?

Migration studies have revealed the importance of the Wash to half a million or more waders each year – birds that spend the whole winter, others that refuel in the spring and vast numbers that rely on the food supplies in the mud to provide the energy for the post-breeding moult. There’s a selection of papers that have included WWRG data here, on the Group’s web-site.

wwrg cr TTThe Group still aims to maintain its general ringing programme, so that a representative sample of the key species carry rings. Colour-ringing projects aim to provide survival estimates for Curlew, Bar-tailed Godwit, Grey Plover and Turnstone, with Greenshank and Black-tailed Godwit colour-rings contributing to migration studies. Birdwatchers who visit the Wash can help by reporting colour-marked birds here, on the WWRG web-site.

WWRG data have been used to help inform decisions about the future of the Wash but the threats keep coming. Studies of migration and seasonal turn-over in numbers contributed hugely to decisions to provide national and international protection to the area and to fend off the 1970s plan to build a freshwater reservoir on the rich mudflats. The information that has been generated by many generations of volunteers over a period of sixty years has been used to manage the level of shellfish exploitation, to inform decisions about wind turbine locations and to manage activities that can cause disturbance.

The Wash Wader Ringing Group is very keen for its data to be used – and not just for impact assessment studies. Click here to learn more.

Diamond Jubilee

PLI

Phil Ireland releasing a Curlew

Over one thousand people are estimated to have contributed to sixty years of the Wash Wader Ringing Group’s activities. We have lived in barns, rolled cars, dug tens of thousands of holes, carried nets for miles, made important catches, had depressing failures, got frostbite, been threatened by surge tides and made friends for life.

In the whole of this period, there have been only two leaders of the Group – Clive Minton (1959-1981) and Phil Ireland (1981-present). Bird ringers, wader biologists and millions of waders owe them both a huge debt of gratitude.

You can read more about the history of WWRG on the Group’s website:

wwrg sunset

Photo at the top of this blog is by Cathy Ryden. Many thanks to her and to other photographers.

Wee quiz:

  • Bar-tailed Godwit – Russia
  • Black-tailed Godwit – Iceland
  • Curlew – Finland
  • Oystercatcher – Norway
  • Sanderling – Greenland
  • Turnstone – Canada

 


GFA in Iceland

Graham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

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Ireland’s wintering waders

blog KN OC

There’s still space for a few Knot

The island of Ireland is a great refuge for wintering waders, washed as it is by the warm waters of the Gulf Stream. It’s just a quick hop across the Atlantic from Iceland for Black-tailed Godwits, Golden Plovers, Redshanks and Oystercatchers. For birds travelling from Siberia, such as Bar-tailed Godwits and Grey Plovers, it’s a longer journey but one that’s well worth making.

If Ireland is such a great destination for shorebirds, why do the latest population estimates reveal a decline of nearly 20% in wader numbers in just five years?

This blog summarises the wader information, published in Estimates of waterbird numbers wintering in Ireland, 2011/12 – 2015/16 in Irish Birds. The totals in the report are split into counts for the Republic of Ireland and Northern Ireland but, given that waders don’t recognise borders, most of the comments in this blog relate to the whole of Ireland. The results for 2011-16 have been compared to the equivalent figures for 2006-11 and set in the context of the totals of wintering waders throughout the East Atlantic flyway, as combined by Wetlands International. The Irish data were collected by the amazing volunteers who make monthly, winter counts for I-WeBS (BirdWatch Ireland & National Parks & Wildlife Service) and WeBS (BTO/RSPB/JNCC in Northern Ireland).

blog paper

Headline figures

Fifteen species are considered in this report. The most numerous are Lapwing and Golden Plover, which account for an estimate over 170,000 individuals between them, whilst the smallest contributions are made by Purple Sandpiper (662) and Greenshank (1317). In total, the average estimated number of waders in the winters during the period 2011-16 is 429,170 birds but it should be noted that this total excludes two widespread and common species – Woodcock and Snipe – as well as the enigmatic Jack Snipe. To update previous estimates for these three species, which were last made using distribution and abundance data collected during Bird Atlas 2007-11 fieldwork, it would be necessary to run a special inland survey. There is also some question about Lapwing and Golden Plover numbers, simply because so many of these birds are found in areas that are not covered by monthly waterbird counts.

Biggest changes

blog SA

The Irish Sanderling population has increased by 13.2% in five years

The combined average winter maximum count of the 15 wader species examined in the report declined by 102,310 birds (19%) in the five-year period between 2006-11 and 2011-16. This is extremely worrying. If Lapwing and Golden Plover are excluded from consideration, as there is uncertainty about the completeness of counts, there are five species that are of particular concern; Knot numbers dropped by more than 40% and Oystercatcher, Dunlin, Redshank and Turnstone numbers by more than 20%. The Purple Sandpiper population estimate dropped by over 30% but relatively small numbers of this species are encountered around the rocky coast of Ireland. The only species to show increases were Sanderling, Bar-tailed Godwit, Black-tailed Godwit and Greenshank.

In a previous WaderTales blog, there is detailed information about population estimates for Great Britain: Do population estimates matter? In Great Britain there were similar rates of decline for Redshank and Turnstone (measured over an eight-year, rather than five-year period) but much smaller falls for Knot, Oystercatcher and Dunlin. The possible causes of the changes in Ireland are discussed in the paper in Irish Birds. They include flyway-scale declines (e.g. Knot and Curlew) and the possibility that more birds from the east are now wintering on the coasts of mainland Europe (e.g. Dunlin and Grey Plover).

blog mixed

European context

Blog tableThe table alongside gives an indication of the relative importance of Ireland, Great Britain and, together, the British Isles to the birds that use the East Atlantic flyway during the winter period. The three columns show the percentage of each species found in each of the three regions. Summarised international counts, as used in the paper, were kindly provided by Wetlands International. In the case of four species, Ireland is host to a significant proportion of the Icelandic breeding population (Oystercatcher, Golden Plover, Black-tailed Godwit and Redshank).

Notes: As mentioned earlier, there are questions about the precision of estimates for Lapwing and Golden Plover, although the population trends are reliable. The Ringed Plover percentage seems high (98% for British Isles) but this may well reflect the fact that the Non-estuarine Waterbird Survey has uncovered significant numbers of the species on the open shores of Great Britain. These extra birds are included in the new totals for GB but not in the flyway total. The percentages for Black-tailed Godwit seem low, as discussed further down.

Ireland is particularly important for Golden Plover, Ringed Plover, Bar-tailed Godwit and Black-tailed Godwit, as well as for the Icelandic subspecies of Redshank. Greenshank is excluded because the percentages are below 1% of the flyway population for Ireland and for Great Britain.

blog BA horiz

11% of Bar-tailed Godwit on the East Atlantic Flyway spend the winter in Ireland

Although there are important populations of breeding waders in Ireland, the shores and wet fields of the island really come into their own during July and August, when the first ‘winter’ waders arrive, and they only become quiet again in April and May, when the last birds head north and east to nest. A successful breeder is likely only to be away for four or five months, meaning that these waders will spend by far the largest part of the year in Ireland. The island is even more important for immature birds. Young Oystercatchers that arrive from Iceland, Scotland or perhaps Norway when just a few months old are likely to spend the next 30 months in Ireland before making their first trip north. There is a WaderTales migration blog about the Oystercatchers that fly from Iceland: Migratory decisions for Icelandic Oystercatchers.

blog OC

Curlew in the Republic

Curlew numbers in the Republic of Ireland illustrate the relative importance of the country for breeding and non-breeding populations. The winter population estimate for Curlew in the Republic is 28,300 but the most recent survey conducted by BirdWatch Ireland and NPWS, as summarised in the WaderTales blog Ireland’s Curlew Crisis, reveals that the number of breeding birds has crashed to just 138 pairs. Accounting for young Irish birds that have not started to breed, and even if we assume that all Irish birds stay in the country for the winter, then the total number of home-grown Curlew seen in non-breeding flocks is at most about 400. This means that every winter flock of 70 Curlew will contain an average of just one Irish bird. Far more deliver their curl-ew calls with a Scottish, Finnish or Swedish ‘accent’. The map below shows the migration pattern for Curlew ringed in or found in Britain & Ireland.

blog migration map

Black-tailed Godwit

In the table above, it looks as if 18% of Iceland’s Black-tailed Godwits spend the winter in Ireland. This is probably an underestimate of the importance of the Republic of Ireland and Northern Ireland to the species. The flyway total for Black-tailed Godwit is given as between 98,000 and 134,000 in the Irish Birds paper and the percentage figure is based on 110,000. These three figures are almost certainly too high, as they build upon country-based estimates that have subsequently been revised. The true figure is likely to be around 60,000 to 65,000 (J. Gill pers. comm.), which would suggest that the maximum winter count in Ireland of 19,800 represents at least 30% of the islandica Black-tailed Godwits. Add in extra birds that moult in Ireland in the autumn, before moving further south to countries such as Portugal, and other birds that spend spring months on the island, and Ireland becomes even more important for Black-tailed Godwits!

blog BTMost birdwatchers might associate flocks of waders with estuaries but Black-tailed Godwit is an excellent example of a species that also relies on inland fields, either close to estuaries or along river valleys. Whilst undertaking PhD research on Black-tailed Godwits in south-east Ireland, Daniel Hayhow showed that there is insufficient time to find enough estuarine food during the mid-winter tidal cycles, with birds topping up their resources on grassland. You can read more about the energetic consequences of choosing to winter in eastern England, Portugal and Ireland in this blog: Overtaking on migration. Site designation and planning decisions need to take account of the grassland feeding requirements of Black-tailed Godwits and other waders that do not spend all of their time on estuaries, particularly Curlew.

Conservation implications

Some of the issues facing waders may be related to threats that species face in the breeding grounds. However, it may be easier to introduce measures that provide better protection and feeding opportunities in the wintering area, as ways of maintaining populations through the non-breeding season, than it is to deal with problems in the High Arctic. (Although we can all help by reducing carbon emissions, in order to minimise global warming, of course).

blog OC SA

Reading the report, I was reminded of the need to consider a range of conservation issues:

  • Care needs to be taken when considering shoreline developments. These can directly remove habitat or squeeze the width of the intertidal zone.
  • Increased harvesting of shellfish can affect species such as Oystercatcher and Knot and brings risks of introducing alien species and diseases.
  • In the drive to cut carbon emissions, tidal, wave and wind power developments need to be sited in appropriate places.
  • Off-shore harvesting of growing kelp beds has been suggested, as a way of producing fertiliser and biofuels. This process could reduce protection for beaches and change the availability of resources for species such as Turnstone and Sanderling.
  • Grassland areas need to be considered (and not just estuaries) when planning protection for species such as Curlew and Black-tailed Godwit.

blog RKPaper

Estimates of waterbird numbers wintering in Ireland, 2011/12 – 2015/16. Brian Burke, Lesley J. Lewis, Niamh Fitzgerald, Teresa Frost, Graham Austin, and T. David Tierney. Irish Birds No. 41, 1-12.

There is a complementary paper in British Birds, covering Great Britain. The wader information is summarised in this blog: Do population estimates matter?


GFA in Iceland

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

@grahamfappleton

Do population estimates matter?

blog top godwitsThis month (March 2019) saw the publication of Population estimates of wintering waterbirds in Great Britain, which includes all the wader species from Little Stint to Curlew. Given that the Wetland Bird Survey already covers about 2000 wetlands and provides annual monitoring, why do we need to know the total number of birds in Great Britain?

I suggest four reasons:

  • If we count the number of Curlew and we have a figure for the European population then we know that Great Britain is responsible for nearly 20% of Europe’s Curlew each winter, thereby strengthening the case for national conservation action;
  • If we have a national figure, then we know that a flock of 2000 Black-tailed Godwit represents (as it turns out) over 5% of the British total, which is a useful criterion when assessing the conservation importance of individual sites;
  • blog GKPopulation totals help to put annual percentage changes into context;
  • And simply because people ask questions such as “how many Greenshank are there in the country during the winter?”

So, here’s the bottom line. In their 2019 review of waterbird numbers in British Birds, a team from BTO, WWT, JNCC & RSPB reveal that an estimated total of 4.9 million waders spend the winter in Great Britain. That’s about one third of all waders on the East Atlantic Flyway. Impressive!

Please note that Northern Ireland figures are included in an upcoming report for the island of Ireland.

Making the counts

The population estimates owe a lot to those who undertake monthly Wetland Bird Survey (WeBS) counts on estuaries, lakes and waterways, during the winter months, year in and year out. Counts from the period 2012/13 to 2016/17 are used in the population estimates that form the basis for the 2019 review. WeBS data have many other uses, as you can read here: Wetland Bird Survey: working for waders.

blog CUFor species of wader that also make use of the open coast, the Non-estuarine Waterbirds Survey of 2015/16 (or NEWS III) provided additional data, updating the NEWS II figures from 2006/07. The vast majority of our wintering Purple Sandpipers are found on open beaches and rocky shores, as well as large numbers of Turnstone, Ringed Plover and Sanderling, together with significant numbers of Oystercatcher, Curlew and Redshank. There’s more about NEWS in this slightly dated blog: NEWS and Oystercatchers for Christmas.

The last assessment of winter wader populations was made by the Avian Population Estimates Panel and published in British Birds in 2013 as Population estimates of birds in Great Britain and the United Kingdom (APEP3). In here, estimates for waders were largely based on WeBS data for the period 2004-09 and NEWS II. The new assessment is presented as Population estimates of wintering waterbirds in Great Britain and also published in British Birds. It uses WeBS information for the period 2012-17 and NEWS III data. Effectively, there is an 8-year or 9-year difference between the two sets of figures.

The biggest losers

blog graphicGreat Britain is extremely important in the context of the East Atlantic Flyway, as is obvious from the fact that the area holds nearly five million waders. The WeBs counts already monitor the ups and downs on an annual basis but this review provides an opportunity to turn the percentages into actual numbers. It is concerning that, over a period representing less than a decade, the average maximum winter count for six of the species that were surveyed dropped by a total of over 150,000. These big losers were Knot, Oystercatcher, Redshank, Curlew, Grey Plover and Dunlin, ordered by number of birds lost, with Knot seeing the biggest absolute decline.

In preparing the new estimates for the British Birds paper, an opportunity was taken to refine the way that populations are calculated, based on Use of environmental stratification to derive non-breeding population estimates of dispersed waterbirds in Great Britain, by Verónica Méndez et al. The new methodology explains some of the differences between percentage changes reported by WeBS and the percentage changes obtained by comparing the latest population estimates to those in APEP3.

blog KN graphic

The Knot estimate dropped from 320,000 to 260,000. This figure is higher than might be expected from the counts that take place at sites covered by WeBS, being larger than the ten-year decline of 14% reported in the last WeBS report. Knot are mobile species within the North Sea and Atlantic Coast wintering area and it is possible that British losses may be explained, at least to some extent, by redistribution.

blog oyc graphThe drop in Oystercatcher numbers from 320,000 to 290,000 appears to be less than 10%, compared to a ten-year decline of 12% on WeBS. Improved analysis of NEWS data helped to add some more birds to the open-coast estimate so the 10% fall may underestimate the seriousness of the Oystercatcher situation. The 25-year Oystercatcher decline on WeBS is 26%, which is not surprising if you look at the changes to breeding numbers in Scotland, where most British birds are to be found. There’s more about this in: From shingle beach to roof-top.

blog RKThe Redshank decline of 26,000 is higher than would be predicted from WeBS figures, suggesting a drop of over 20% since APEP3, rather than ‘just’ 15% for the ten-year WeBS figure. This is a species that also features strongly in the Non-estuarine Waterbird Survey and that might explain the difference. Wintering Redshank are mostly of British and Icelandic origin, with the Breeding Bird Survey (BBS) suggesting a ten-year decline of 24% in our British breeding birds.

The Curlew is now globally recognised as near-threatened. The latest winter estimate is 120,000, down from 140,000 in APEP3. The new total represents between 14% and 19% of the European population, which means that we have a particular responsibility for this much-loved species. Only the Netherlands holds more wintering Curlew than Great Britain. Is the Curlew really nearly-threatened? is one of several blogs about Curlew in the WaderTales catalogue at www.wadertales.wordpress/about .

blog 2 DNIt has been suggested that the long-term declines of Grey Plover and Dunlin  may be associated with short-stopping, with new generations of both species wintering closer to their eastern breeding grounds than used to be the case. WeBS results indicate a 31% drop in Grey Plover and a 42% drop in Dunlin, over the last 25 years. There was a loss of 10,000 for both species between APEP3 and the new review, representing declines of 23% and 3% respectively.

The biggest winners

There are four big winners in the period between APEP3 (2004-09) and the new review (2012-16), although, even here, not all as it seems.

The Avocet has seen further dramatic gains. with the estimated wintering population rising to 8,700. The increase is not quite as big as might have been expected, based on the 43% rise seen in ten years of WeBS counts, but it is still a dramatic continuation of a 40-year trend.

The numbers of Bar-tailed Godwit and Ringed Plover are both substantially higher but at least a proportion of each of these changes is linked to the better coverage and more sophisticated sampling methods that were discussed earlier. Bar-tailed Godwit increases may also reflect redistribution around the North Sea.

blog BW graphOne of the consequences of improved statistical techniques, as used this time around, is the apparent decline in the estimated population of Black-tailed Godwit. The new figure of 39,000 is 4,000 smaller than in APEP3, despite the fact that the WeBS graph clearly shows an increase. Interpolation using WeBs figures suggests that the earlier population estimate should have been 31,000, rather than 43,000.

There are other winners too, as you can read in the paper. At the start, I posed the question “how many Greenshank are there in the country during the winter?”.  The answer is 810, representing an increase of 200 since APEP3.

Game species

The estimates for the three wintering waders that are still on the UK quarry list have not changed since APEP3 (published in 2011) as there are no new data available.

Golden Plover: The winter estimate remains as 400,000, as there has been no comprehensive, winter survey since 2006/7. Large numbers of Golden Plover arrive from Scandinavia, Europe and Iceland in the late summer, joining the British birds that choose not to migrate south or west. The GB breeding population is probably less than 50,000 pairs. Most breed in Scotland which has seen a breeding decline of 23% in the period 1995 to 2016 (BBS). Golden Plover is still ‘green listed’.

snipe-headerSnipe (Common): The winter estimate remains as 1,100,000 – a figure that was acknowledged in APEP3 as being less reliable than that of most species. At the same time, the GB breeding population was estimated as 76,000 pairs, indicating at least a 4:1 ratio of foreign to British birds, and that does not take account of the number of British birds that migrate south and west. Snipe are ‘amber listed’ but BBS suggests a recent increase of 26% (1995-2016). There is a WaderTales blog about  Snipe and Jack Snipe.

Woodcock: The winter estimate remains as 1,400,000 – another figure that is not considered to be particularly precise, with much variation between years. The diminishing breeding population is dwarfed by winter numbers, as you can read in this WaderTales blog, with increased attention being given to ways to afford better protection of red-listed, British-breeding birds.

January counts

blog BTThe paper in British Birds also includes a table of January population estimates, to provide data that are comparable to mid-winter counts in other countries. These figures are used in waterbird monitoring for the International Waterbird Census for the African Eurasian Flyway. The main table (and figures mentioned above) are average maximum winter counts (in the period September to March). Black-tailed Godwit is one species that illustrates the difference, with a mean of 30,000 in January and a mean peak count of 39,000. Having moulted in Great Britain, some Black-tailed Godwits move south to France and Portugal in late autumn, returning as early as February. January counts are therefore substantially lower than early-winter and late-winter counts. There is more about the migratory strategy employed by Black-tailed Godwits that winter in southern Europe in Overtaking on Migration.

Looking forward

blog BB coverThe authors have done a tremendous job. They have refined the way that estimates are calculated, they have combined the results from WeBS and NEWS III, and they have delivered population estimates for 25 wader species and many more other species of waterbirds. These population estimates will be used in conservation decision-making until the next set of numbers becomes available. Meanwhile, thousands of birdwatchers will count the birds on their WeBS patches in each winter month, every year. Without them, this paper could not have been written.

Before the next assessment, there will need to be another NEWS survey, to check up on species that use rocky and sandy shore birds, such as Purple Sandpipers, Turnstone and Curlew. Hopefully, there will also be a dedicated survey to assess Lapwing and Golden Plover numbers and perhaps we might find a way to refine the old estimates for Woodcock, Snipe and Jack Snipe.

Paper

Population estimates of wintering waterbirds in Great Britain. Teresa Frost, Graham Austin, Richard Hearn, Stephen McAvoy, Anna Robinson, David Stroud, Ian Woodward and Simon Wotton. Published in British Birds Volume 112. March 2019.

British Birds is a subscription journal. The issue containing this paper can be purchased separately. At some stage, the paper will become free-to-view.

blog flying godwits

 


GFA in Iceland

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

@grahamfappleton

Well-travelled Ringed Plovers

Waders breeding in Chukotka, in the north-east corner of Russia, have a long way to travel at the end of the summer, in search of suitable habitats in which to spend the non-breeding season. A new study, using geolocators, shows that Ringed Plovers from this area fly between 8,900 and 12,100 km each autumn and in a very different direction to most other shorebirds that breed in the same area.

RP no geolocatorThis blog is based on a new paper in Wader Study, written by a team led by Pavel Tomkovich of the Moscow Zoological Museum. Their study describes the seasonal movements of tundrae Ringed Plovers from the easternmost edge of the subspecies’ distribution.

Pavel and his colleagues work in the south-eastern part of Chukotka, the region of Russia that is bounded by the Pacific Ocean to the east and the Arctic Ocean to the north. The data used in the paper were collected from five males that carried geolocators on their journeys to and from their wintering locations. Incredibly, during the mid-winter period, the birds were scattered from the Persian Gulf to the Nile Delta and south to Somalia, all of which are a very long way from Chukotka.

Range and distribution

RP snowy welcoms.jpg

Scene awaiting Ringed Plovers arrive in Chukotka in spring

Ringed Plovers breed over much of the Arctic region, from Greenland (and the eastern fringe of the northern Canadian islands), eastwards through northern Norway and right the way across Russia to the far eastern corner of Chukotka. The missing piece of the Arctic, between Newfoundland in eastern Canada and the western islands of Alaska, is the home of the very similar Semipalmated Plover. Additionally, there is a latitudinal spread in Ringed Plovers, with pairs in Europe breeding from Iceland throught to France.

Ringed Plovers breeding in the west

TTFReaders in Britain & Ireland will see Ringed Plovers in every month of the year. A colour-ringing study in Norfolk showed that many marked birds remained near their breeding sites for the whole year, while others migrated in a variety of directions in the autumn, exemplified by individuals flying south to France, north to Scotland and west to Ireland. In the spring, we see a strong passage of birds that have been wintering in countries in western Africa and southern Europe. They are on their way to breeding areas in Canada, Greenland and Iceland, in the west, and (to a lesser extent) Scandinavia in the north.

Ringed Plovers breeding in the north and east

Ringed Plovers breeding along the Arctic coastal fringe of Russia were believed to winter in eastern and southern Africa, right down to the southern tip of the continent. This new study, written up in Wader Study, the journal of the International Wader Study Group, is the first to reveal the migration routes of birds from the very far east of the range. The results are amazing, as illustrated by the map below which shows the movements of one male bird that wore a geolocator for a year. During that time he flew north-west to the Arctic coast of Siberia, south-west and south to Somalia, returning home through Siberia in the spring by a more southerly, inland route. His annual migrations totalled 25,000 km.

Global map

The migration route of one Ringed Plover. Map provided by Ron Porter

In the paper, the authors map and discuss the journeys of this Ringed Plover and four other males, in great detail. The ultimate winter destination of the birds that are not shown in this blog were the Nile Delta, the Persian Gulf (2) and the Red Sea. Unlike some other wader species, the migration strategy of Ringed Plovers is to use a wide range of suitable wetlands (often small and temporary) for only brief stops. It is unusual to see large flocks; the only important staging area to be identified so far, across the whole of Asia, is in north-central Kazakhstan.

Global perspective

global illustrationChukotka attracts birds from across the world. As well as Ringed Plover that fly here to breed from North Africa and the Arabian Peninsula, there are Knot from Australia and New Zealand, Semipalmated Sandpipers from South or Central America and Spoon-billed Sandpipers from anywhere from India to China – just to select three species that share the tundra with Ringed Plovers. The diagram alongside hints at the many different directions in which birds depart at the end of the breeding season. It’s really quite amazing!

RP three spcies

The Chukotka melting-pot: Knot from Australasia, Semipalmated Sandpiper from the Americas and Spoon-billed Sandpiper from Asia.

Historical perspective

Most Chukotka waders follow the East Asian-Australasian Flyway and it may seem surprising that Ringed Plovers are so different. The authors suggest that bird migration routes repeat the direction of expansion of a species’ historical breeding range, which will have changed markedly since the last Ice Age. In the late Pleistocene, Ringed Plovers may have had a largely Western Palaearctic breeding distribution with migration south to Africa each autumn. As the ice melted, and large areas of suitable habitat became available, the breeding distribution may have expanded eastwards, with these eastern breeders continuing to winter in Africa but travelling a lot further in autumn and spring.

Read the full paper here

RP geolocatorTranscontinental pathways and seasonal movements of an Asian migrant, the Common Ringed Plover Charadrius hiaticula tundrae. Pavel S. Tomkovich, Ron Porter, Egor Y. Loktionov & Evgeny E. Syroechkovskiy. Wader Study 124(3)

Further Reading in WaderTales

If you would like to learn more about migration to, from and through Britain & Ireland, have a look at Which wader, when and why?

RP lesser sandplover

Lesser Sandplover is one of the Chukotka species that migrates via the Yellow Sea

Geolocators are providing new and important information about migration but they need to be used safely. There’s a review here that will be of interest to anyone who is thinking of attaching devices to birds: Are there costs to wearing a geolocator?

There is a lot of concern about species such as Knot and Spoon-billed Sandpiper that breed in Chukotka and rely upon resources in The Yellow Sea. Read more in Wader declines in the shrinking Yellow Sea.

 

RP habitat


 GFA in Iceland

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

@grahamfappleton

 

 

Wader declines in the shrinking Yellow Sea

An important paper by Colin Studds and colleagues shines a spotlight on the Yellow Sea, where waders/shorebirds have lost vast areas of feeding habitat during China’s economic boom.

headerWaders make some of the most remarkable migratory journeys in the bird world and many rely on a few key estuaries to refuel, especially as they head north to breed. For hundreds of thousands of waders on the East Asian-Australasian Flyway, from tiny Red-necked Stints to Far Eastern Curlews, the Yellow Sea is absolutely crucial. A new paper by Colin Studds and sixteen colleagues collates the available information on current population trends of waders using this flyway and shows how these relate to the reliance of each species on the Yellow Sea. The more a species relies on disappearing mudflats, between China and the Korean peninsular, the faster it is declining.

As Colin Studds says: “Scientists have long believed that loss of these rest stops could be related to the declines, but there was no smoking gun.” Now there is. The new paper is published in Nature Communications.

Rapid population decline in migratory shorebirds relying on Yellow Sea tidal mudflats as stopover sites (Nature Communications 8:14895 | DOI: 10.1038/ncomms14895)

Establishing the routes

barwit

Bar-tailed Godwits make epic migratory journeys

Over the last twenty years, satellite tracking has revealed the amazing migratory journeys of shorebirds on the East Asian-Australasian Flyway. The most famous wader ever must be E7, which was the first Bar-tailed Godwit to be tracked from Alaska to New Zealand in one continuous journey, covering the 11,600 km journey in 9 days. When E7 flew from New Zealand to the Yellow Sea in the next spring, on the first leg of its return journey, that was another flight of 10,200 km in 7 days.

It’s not just Bar-tailed Godwits that link New Zealand and Australia to the Yellow Sea. Colour-ringing has established that at least 10 wader species use this staging area during their northward migration in spring.

Counts by Birdwatchers

FE Curlew standing

Far Eastern Curlew is one of the fastest declining species on the flyway. There is a WaderTales blog about the global plight of members of the curlew/godwit family here.

Annual counts of waders have been taking place in sites across Australia and New Zealand since the early 1980s. Colin Studds and his colleagues use data collected during the non-breeding seasons between 1993 and 2012 from 43 of these key locations. The analysis relies on the work of scores of volunteer birdwatchers who undertake these counts during the months from October through to March. The count data used in this paper focused on December and January, when there is least likelihood of within-season movement. Some of the declines have been dramatic; in twenty years, the number of Far Eastern Curlew fell by about 60%, with a 75% drop in Curlew Sandpipers, just to give two examples.

If numbers are going down, then that suggests that these waders are failing to breed as successfully as they once did or that the adults themselves are dying in larger numbers than used to be the case – or both. The fact that no changes have been observed in the proportion of juveniles in flocks strongly suggests that survival rate is the key demographic parameter upon which to focus when trying to understand population declines.

Declining survival rates

Colour-ring observations not only establish migratory links, they also provide the raw data from which annual survival rates can be estimated. A typical annual survival rate for an adult wader is between around 70% and 90%. If the survival rate is 90%, and 50 female waders lay an average of 4 eggs during a breeding season, then only 10 of the chicks need to hatch and reach breeding age for the population to remain stable. If that same level of productivity occurred but the survival rate for adults changes to 80%, then the chance of an adult dying in any given year doubles and the population will drop by half in just six years. This illustrates that a fall in survival of just 10% can have serious implications for the population trajectory.

great knot

Changing Great Knot survival from 86% to 68% could reduce life-expectancy by two-thirds

The counts of non-breeding waders in Australia suggested that there were major changes in numbers for several species between 2010 and 2012. When Theunis Piersma and colleagues analysed the colour-ring sightings for populations of three species that spend the non-breeding season in Australia and breed in eastern Siberia – Bar-tailed Godwit, Great Knot and Red Knot – they discovered a decline in annual survival of between 18% and 19% in just two years. Their paper raised serous alarm bells. All three populations spend time in the Yellow Sea on their spring migration and Theunis argued that rapid habitat loss in the Yellow Sea was the most likely explanation of reduced summer survival, with dire (but uncertain) forecasts for the future of these flyway populations.

survival table

There is a global review of survival rates in this paper: Méndez, V., Alves, J. A., Gill, J. A. and Gunnarsson, T. G. (2018), Patterns and processes in shorebird survival rates: a global review. Ibis. doi:10.1111/ibi.12586. The paper is summarised in this WaderTales blog: Measuring shorebird survival.

Reliance on the Yellow Sea

plate1-melville-barwits-under-assault

Bar-tailed Godwits watch on as their habitat disappears (Dave Melville)

It is estimated that nearly 30% of Yellow Sea tidal mudflats have been lost to coastal development in the last 30 years and China is forecast to undergo up to 14% expansion in urban development over the next 15 years, much of it concentrated on the margins of the Yellow Sea. Within the remaining mudflats, there have been increases in algal blooms, heavy metal deposits and areas of invasive Spartina alterniflora, the last of which reduces mudflat availability. All of these changes have the potential to put huge pressures on waders that are fattening up for the last leg of their migratory journey to arctic breeding grounds.

Previous work focused on waders in Japan, by Tatsuya Amano and colleagues, had shown that wader species relying on the Yellow Sea while on migration are declining more quickly than those that are not but Japan is on the migratory flyway so this result could have been confounded by changes in migratory route. By using data from the the non-breeding season and looking at a wider range of species, Colin Studds and his colleagues have been able to link reliance on the Yellow Sea with the magnitude of population changes.

Main graphA key element of the new paper is the compilation of available data on flyway population sizes, migratory connectivity and Yellow Sea count data, in order to estimate the proportion of each species that rely upon the Yellow Sea. At the lowest end is the Grey-tailed Tattler, only 3% of which use the area, whilst 100% of the menzbieri subspecies of Bar-tailed Godwit rely on the Yellow Sea. When reliance is plotted against annual population trend the fit is remarkable. Interestingly, there are two very similar subspecies in the analysis; whilst the menzbieri Bar-tailed Godwits are estimated to have been declining by 6.1% per annum, the baueri subspecies, which is only 50% reliant on the Yellow Sea, has ‘only’ been declining at 1.4% per annum. 

Emerging Conservation Action

Good newsThis paper provides further evidence of the huge importance of the Yellow Sea. To quote Richard Fuller, the team leader of this research “Every country along the migration route of these birds must protect habitat and reduce hunting to prevent the birds declining further or even going extinct.”  Issues facing birds that use the flyway are being successfully highlighted by the East Asian-Australian Flyway Partnership. Australia has signed agreements with China, Korea and Japan to protect migratory birds, and China and South Korea have recently begun the process of listing parts of the Yellow Sea as World Heritage Sites. As well as development controls, a range of mitigation actions are discussed in the paper – let’s hope that they are pursued with enthusiasm.

Update – January 2018

“Great news for shorebirds! China to halt coastal land reclamation”. Read more in this BirdLife International article.

The paper is free to download

GK flockThe results of this study have been published as Rapid population decline in migratory shorebirds relying on Yellow Sea tidal mudflats as stopover sites (Nature Communications 8:14895 | DOI: 10.1038/ncomms14895)

The authors are: Colin E. Studds, Bruce E. Kendall, Nicholas J. Murray, Howard B. Wilson, Danny I. Rogers, Robert S. Clemens, Ken Gosbell, Chris J. Hassell, Rosalind Jessop, David S. Melville, David A. Milton, Clive D.T. Minton, Hugh P. Possingham, Adrian C. Riegen, Phil Straw, Eric J.Woehler & Richard A. Fuller.


 GFA in Iceland

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

@grahamfappleton

 

A place to roost

Safe roost sites are important for waders such as Black-tailed Godwits

top-picIt has been said that Black-tailed Godwits are the laziest birds in the world, usually in a frustrated tone while waiting for a marked bird to wake up and reveal the rest of its colour rings. Roosting is not laziness, however; it’s an important resource conservation strategy in the daily balance of energy inputs and outputs.

When Black-tailed Godwits are feeding in tidal systems they have a limited amount of time each day to access the shellfish and worms that make up their diet. These foods are unavailable over the high-tide period, and sometimes in the lull between the ebb and flood, so birds conserve energy by gathering together at roosts. They seek out sites that are safe and sheltered, and then go to sleep – often for several hours if undisturbed. Theunis Piersma and colleagues have shown that sleep is the most energy efficient form of activity for shorebirds.

In two interesting papers, focusing on Red Knot and Great Knot in Roebuck Bay, North-Western Australia, Danny Rogers and colleagues showed that choice of roost sites seems to involve several criteria:

  • Birds try to find a roost as close as possible to feeding sites, probably to reduce travel costs between feeding areas and high-tide roosts.
  • In particular, birds appear to turn down feeding opportunities that take them further from preferred roost sites.
  • Open roosting sites that provide clear views of any approaching predators seem to be preferred
  • Availability of safe night-time roosts seems to be more restricted, with birds flying further to find a suitable site to wait out the high tide period.
  • The estimated ‘commuting costs’ associated with flying to and from these roosts accounted for between 2% and 8% of daily energy expenditure.
  • Flocks of Knot that were disturbed at roosts and forced to fly around for thirty minutes had an estimated increase in their daily energy expenditure of c 13%.
  • roosting-curlew

    These Curlew, roosting on the shores of the Humber, are minimising energy expenditure in very cold conditions

    Temperatures in Roebuck Bay can frequently exceed 38⁰C, and the waders chose wet sites in which they could keep their feet and legs cool. That’s not a problem for waders wintering in the UK.

The details can be found here:

What does this mean for Black-tailed Godwit in UK conditions?

turnstone-header

Waders often roost in mixed flocks. These birds are resting on an Icelandic beach after crossing the Atlantic

Although the facts, figures and conclusions listed above relate to Red Knot and Great Knot, the authors point out that they gather in mixed roosts with other species to which similar decision-making might apply. The Australian studies took place in very hot conditions but many of the factors influencing roosting site choice are likely to also apply to our cold and wind-swept estuaries in NW Europe. For instance, a study of Knot on the Dee Estuary by Mitchell et al in England estimated that costs of commuting to roosts could account for 14% of daily energy expenditure.

energy-figEnergetic constraints are likely to present different issues for arctic waders that spend the non-breeding season in the northern hemisphere than for ones that choose to cross the equator, and experience warmer conditions and heat stress. Even within Europe, the energetic balances that waders can experience on different estuaries can vary widely. In their 2013 Ecology paper on Black-tailed Godwit energetics, Costs, benefits, and fitness consequences of different migratory strategies  José Alves and colleagues showed that mild weather and abundant food supplies result in a positive energy balance for godwits wintering on the Tagus estuary in Portugal and, to a lesser extent, the estuaries of south Ireland. In east England estuaries, however, the costs of keeping warm can sometimes exceed the energy available from the food supplies (see figure). In such circumstances, an undisturbed roost, located as close as possible to feeding areas may well be especially important.

Consequences of roost loss

redshank

Colour-marked Redshank demonstrated the individual consequences of habitat loss

Although it is very hard to demonstrate population-level consequences of removing roosting sites, we have some clues about how birds respond to removal of roosts and foraging sites, from impact-assessment work carried out by the BTO on Redshank in the Cardiff Bay area. When this bay was closed and flooded for commercial development, Redshanks lost both feeding areas and traditional roosting sites. Tracking of colour-ringed Redshanks showed that displaced birds moved to new feeding areas and roost sites up to 19 km away, but mostly stayed close-by, on the mudflats of the River Rhymney. Cannon-net catches of these flocks provided measurements of bird mass before and after the closure of the Bay, which revealed that adult Redshank from the Bay had difficulty in maintaining body condition in the first winter following closure and that their survival rates in subsequent winters remained lower than birds that had previously been settled in the Rhymney area. Three papers are essential reading for anyone interested in the consequences of displacements caused by development projects.

ynrx-for-blogA key point of both the Knot work in Australia and the Redshank impact assessment study in Wales is the energetic costs to individuals that can result from the disruption caused by the loss of roosting or foraging sites. Indeed, individual waders may even have favoured locations within roosts that they consistently use. For example, at Gilroy Nature Park, a shallow pool where up to 3500 of the Black-tailed Godwits that feed on the Dee estuary in NW England regularly gather to roost, observers of colour-ringed birds have noticed that marked individual godwits (eg YN-RX pictured here) are often seen in exactly the same place within the pool and flock.  Losing a roosting site of which individuals have such detailed knowledge, and forcing flocks of birds to find alternative roosting locations, may therefore have bigger consequences than just the kilometres covered.

Importance of individual sites

mapThe total number of Icelandic Black-tailed godwits was estimated to be 47,000 in 2004, a figure that is likely to be closer to 60,000 now as the population has continued to grow. This means that a flock of 3,000 birds represents about 5% of the total of the entire breeding population. There is a small number of sites across the United Kingdom that hold these sorts of numbers at different stages of the year. According to the latest figures from the Wetland Bird Survey, numbers on the Wash and Humber estuaries in east England peak at averages of 8198 and 3413 in September, there are 4339 Black-tailed Godwits on the Welsh side of the Dee estuary in October and 5909 on the English side in November. The mean count on the Thames also peaks in November (5883). As the winter progresses, numbers on the nearby Ribble estuary rise to a mean of 4234 in January, there is a mean maximum of 3236 on the Washes in February and 3191 on the Blackwater in March. Although all of these sites are important to Icelandic Black-tailed Godwits throughout the non-breeding period, the different timing of peak counts illustrates the reliance of Icelandic birds on a network of sites. To get a feel for the range of strategies used by individual birds, see Godwits and Godwiteers.

Conservation

horse-and-flock

Roosting Black-tailed  Godwits at Gilroy Nature Reserve share their pool with a horse and Canada Geese

While estuarine feeding areas across Europe are well safeguarded, through the network of Special Protection Areas, roost sites are not always as well served, especially if birds spend the high tide period on sites outside the SPA boundary of their foraging areas, such as the freshwater pool at Gilroy Nature Reserve, inland of the Dee Estuary. Some roost sites such as North Killingholme Haven Pits on the Humber have been included within a designated SPA formed by the adjacent mudflats but others, such as Gilroy, are discrete sites outside the SPA. Maintaining the wader populations that forage on our estuarine mudflats may depend upon our capacity to protect their safe roosting sites, even if they are not currently designated.


GFA in Iceland

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

@grahamfappleton