Oystercatcher Migration: the Dad Effect

What determines whether some birds migrate and others do not? This question is fundamental to understanding how migratory systems change over time but the causes of individual migratory behaviours have proved difficult to isolate.

Verónica Méndez and colleagues are studying Icelandic Oystercatchers, some of which remain in Iceland for the winter but most of which migrate across the Atlantic to Ireland, Britain and mainland Europe. In a 2021 paper in Scientific Reports they show that a chick’s migratory behaviour seems to align with the behaviour of its father but not its mother. What can explain this pattern?

The story so far

The Icelandic Oystercatcher study system has already featured in three WaderTales blogs. The first was Migratory decisions for Icelandic Oystercatchers. This focused upon the key questions that Verónica Méndez and colleagues from the universities of Iceland, East Anglia (UK) and Aveiro (Portugal) are trying to answer.

  • Why do some Oystercatchers migrate when others don’t?
  • Is it the same birds each year?
  • Do resident or migrant birds have an advantage when it comes to choosing a territory and raising chicks?
  • Do chicks follow the same migratory patterns as their parents?

When the first blog was written, in 2015, eight colour-ringed Oystercatchers had been seen in Ireland and the UK, and five had been seen wintering in Iceland. Fast forward to the next blog in 2018 – Mission impossible? Counting Iceland’s wintering Oystercatchers – where counts showed that over 11,000 Oystercatchers spend the winter in Iceland. Using colour-ring sightings of resident and migratory birds, the research team concluded that this total is about 30% of the whole Icelandic population. The other 70% fly south across the Atlantic each autumn, with no individuals yet observed to change what they do between years.

In the third blog – Which Icelandic Oystercatchers cross the Atlantic? – some patterns were starting to emerge.

  • Females and males are equally likely to migrate.
  • Size does not matter – small and big birds are equally likely to migrate
  • There are regional patterns across Iceland, with birds breeding in the west being most likely to be resident.
  • Birds do not pair up assortatively – residents don’t pair up with other residents before the migrants return, for instance.

Family ties

In most species of waders, parents protect their chicks and take them to suitable feeding areas but they do not actively feed them. Parental care in European Oystercatcher includes foraging for food and bringing it back to the chicks. This is why it is possible for Oystercatchers to nest on the roofs of buildings (Oystercatchers: from shingle beach to roof-top), where they are out of the reach of ground predators.

Focusing on chicks

To be able to understand the relationship between migratory behaviour in adults and their chicks, you need to be able to mark and then attempt to follow all of the members of a family. Adult Oystercatchers generally keep the same mates and nest in the same areas year after year, enabling the establishment of marked population of birds in different parts of Iceland. Between 2015 and 2018, a total of 615 incubating adults were caught. By following the outcomes of nesting attempts and then monitoring the growth of chicks, the research team also managed to individually mark 377 chicks.

Three colour-ringed chicks. Where will they go?

The success of the whole project relied heavily upon winter sightings of marked birds within Iceland and in Ireland, the UK and continental Europe. Through a network of volunteer observers reporting sightings of marked individuals across the wintering range, the migratory behaviours of 227 of the 615 colour-marked adults and 50 of the 377 colour-marked chicks had been identified at the time that this paper was written. In addition, it was possible to infer the migratory behaviour of 353 marked adults using measurement of isotope ratios (δ13C and δ15N) of feathers that were grown in the winter (as described here).

The analyses in the paper by Verónica Méndez and her colleagues are based upon 42 marked chicks of parents for which the migratory behaviour of both parents is either known or can be inferred from isotopic signatures. These chicks all fledged successfully and were seen during the winter period, either in Iceland or having crossed the Atlantic. In three cases, two chicks from the same broods are known to have behaved in the same way. More data have become available since the analyses, all confirming the same patterns.

Results

It is possible to imagine a scenario in which late or slow-growing Oystercatcher chicks might be more likely to stay in Iceland than their more mature counterparts – simply by developing too late to gain enough resources to cross the Atlantic. Analysis of hatch dates and growth parameters did not suggest the existence of such a link, as described in the paper.

This young Oystercatcher was spending its first winter on the coast of western Iceland

The interesting finding of this study is the link between the behaviour of parents and chicks. Data generated by observations of colour ringed individuals (adult and chicks) and from isotopes (adults) established 21 chick/parent associations.

  • Of the sixteen chicks raised by migrant mothers, eight migrated and eight remained in Iceland.
  • Of the five chicks raised by resident mothers, three migrated and two remained in Iceland.
  • All ten of the chicks raised by migrant fathers migrated from Iceland.
  • Of the eleven chicks raised by resident fathers, one migrated and ten remained in Iceland.
  • Seven chicks that fledged from pairs with one resident and one migrant parent adopted the migratory behaviour of the father.

This is pretty compelling evidence that chick migratory behaviour is associated with paternal (and not maternal) migratory behaviour!

What does this mean?

There is no evidence of genetic control of migratory destinations and both Oystercatcher parents care for chicks, so what mechanism could produce such strong paternal but not maternal effects?

The authors suggest that the migratory behaviour of individual oystercatchers may be linked to social interactions they experience during the post-fledging period. In shorebird species, such as Oystercatchers, mothers commonly depart before the chicks fledge, or at about the same time. Fathers often provide parental care for longer and this extended period of the parental bond may underlie the link between paternal and juvenile migratory behaviour in Icelandic Oystercatchers. Despite being able to fly and feed independently, juvenile Oystercatchers in Iceland have been seen begging for food several months after fledging, suggesting that some parents (most likely fathers) may care for youngsters much longer than in other species.

This Iceland-ringed Oysterctatcher was photographed in Guernsey in January 2021. It departs at the start of February each year.

Under this extended-care system, a chick that is being look after by a resident male may well become a resident, simply by following dad. As autumn arrives, the youngster can follow his parent when he moves to the coastal mudflats where resident Icelandic Oystercatchers spend the non-breeding season. Autumn turns to winter and the chick is destined to be a resident.

Is it possible to explain a similar link for migrants? As the breeding season comes to an end, migrant fathers leave their breeding areas and head south, across the Atlantic, leaving fledged youngsters to fend for themselves. Groups of youngsters gather together in flocks which also include adults that are feeding up in preparation for migration. Although not influenced by their own fathers, chicks may follow the cues of other migratory adults, thereby creating the patterns seen in this paper.

Most of the chicks included in these analyses were early-fledged birds, simply because earlier nesting attempts tend to be more successful. The research team were unable to detect any significant effect of fledging date on migratory behaviour but they do not rule out the possibility that late-fledging individuals lack the time or resources to undertake a migratory journey, irrespective of paternal behaviour.

The broader context

Migratory behaviour typically arises in seasonal environments, allowing individuals to exploit peaks of resource abundance in distinct locations across the world. Rapid shifts in the distribution and migration phenology of many migratory species present challenges to site-based conservation strategies. There is an urgent need to understand the processes that influence individual migratory behaviour, in order to attempt to predict species’ responses to environmental change.

The findings in this paper suggest that the social interactions experienced by individuals can directly influence the development of their migratory behaviour, and that the extent and timing of parental care may be key in shaping individual access to these social interactions. You can read the full paper here:

Paternal effects in the initiation of migratory behaviour in birds Méndez V., Gill, J.A., Þórisson, B., Vignisson, S.R., Gunnarsson, T.G. & Alves J.A.


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.

Cycling for waders

This blog is mostly about Black-tailed Godwits but there’s stuff about cycling too!

If you’re a Black-tailed Godwit, a 2800-mile (4500-km) direct flight from East Anglia to West Africa is estimated to burn 1085 Calories (4500 kJ) of energy (Alves & Lourenço). Fuelled by Cambridgeshire worms, a female godwit that was raised by the Project Godwit head-starting team flew from the Nene Washes to wetlands in south-east Mauritania in just two days. ‘Cornelia’ – as she was named – undertook this marathon journey with no pre-season training. She just took off on 13th August and arrived on the 15th.

To raise money for Project Godwit and for research projects funded by the International Wader Study Group, Jen and Mark Smart cycled from Somerset to East Anglia, on a 600 mile (960 km) journey that links sites that have been visited by head-started Black-tailed Godwit chicks. Each of them burnt 15,000 Calories (62,800 kJ) over the course of eight days, taking in high energy foods as they travel and stopping to feed and rest each night. Unlike Cornelia, Mark and Jen had been training for years.

Quick reminder of head-starting

Black-tailed Godwits breeding in East Anglia face huge challenges, as you can read below. Four years ago, their situation had become so perilous that it was decided that the only way to stop them disappearing completely was to hatch eggs in incubators and raise chicks in captivity. You can read more about head-starting here. Project Godwit is a partnership between RSPB and WWT, with major funding from the EU LIFE Nature Programme, the HSBC 150th Anniversary Fund, Natural England, the National Lottery Heritage Fund through the Back from the Brink Programme, Leica and the Montague-Panton Animal Welfare Trust.

The maps below show the two breeding sites (Ouse and Nene Washes) and all the late-summer passage sites where head-started birds have been seen in England (left), and the international sightings of all godwits ringed in these breeding sites.

International Wader Study Group (IWSG)

The International Wader Study Group brings together everyone who has a passion for waders (shorebirds), the habitats they use and their conservation. Members include research scientists, citizen scientists and conservation practitioners from all around the world. IWSG gives out small grants each year that help to support wader projects around the world. Recent grants have been used to discover the wintering areas of Common Sandpipers, to measure the site-faithfulness of Dotterel and to support projects in Azerbaijan, Albania, Bangladesh & Argentina.

Mark and Jen

Jen Smart has worked for the RSPB for 14 years.  As a scientist, she led RSPB’s research into the conservation problems faced by breeding waders and developed solutions to help these species. See the WaderTales blog Tool-kit for wader conservation. She developed the science programme around Project Godwit and maintains a keen interest in the project. Jen is Chair of the International Wader Study Group.

‘Manea’ arrived at Old Hall Marshes (Kent) with his sister, ‘Lady’, in July 2017

Mark has worked for the RSPB for 26 years and is Senior Site Manager at Berney Marshes, a 600 ha grassland nature reserve with around 300 pairs of breeding waders. See the WaderTales blog Managing water for waders. As well as managing the reserve, Mark works with other land managers across the country to develop and implement ways of improving habitats for breeding waders.

Latest news from Project Godwit

Project Godwit has been trialling the use of head-starting (https://projectgodwit.org.uk/), where young godwits are reared in captivity, safe from predators and potential flooding, and released once fledged. The aim is to boost the number of godwits breeding in England. The cycle route for Mark and Jen links eleven nature reserves in England, managed by a range of conservation organisations, where head-started Black-tailed Godwits have been spotted on migration by local birdwatchers.

Nelson is one of the birds carrying a geolocator but he has not been recaught (yet)

The ride started at WWT Steart Marshes in Somerset; visited by a Black-tailed Godwit named ‘Nelson’ in 2017. Birdwatchers throughout England were put on alert when the first head-started Black-tailed Godwits were released in 2017 but it was a surprise when Nelson headed southwest. Nelson is a star of Project Godwit. He returned to the Ouse Washes in 2018 and paired up with another head-started bird called ‘Lady’. They have met up in each subsequent spring. In February, Nelson spends time on the Tagus Estuary in Portugal but we don’t know whether he is one of the limosa Black-tailed Godwits that winters south of the Sahara.

The map below shows the route taken by Mark and Jen. The original plan was to cycle from Norfolk to the IWSG conference in Germany, which neatly linked the two causes for which they are seeking sponsorship – Project Godwit and the IWSG fund to support wader research. When the conference was rescheduled as an on-line meeting, they decided to join up the godwit dots across England. The 600-mile bike took just over a week.

Jen & Mark’s route links RSPB, WWT, Wildlife Trustand county wildlife sites between Somerset and Cambridgeshire.

The last site to be visited was the Nene Washes where, as mentioned above, the Black-tailed Godwit ‘Cornelia’ returned to breed. Having been raised at Welney, she was released at the Nene Washes on 27 June, 2018, wearing a small geolocator attached to a flag on her lime ring (see earlier picture). She is the only bird for which the RSPB and WWT team have a whole-year migration history. Cornelia was caught on a nest at the Nene Washes in 2019 and her geolocator was removed. In his blog on the Back from the Brink website, Mo Verhoeven shares his excitement when he learned that this young bird had flown directly from the Nene Washes to wetlands in Mauritania in just two days. There is more about Cornelia here.

Conservation challenges

Wetlands are under threat across the globe and it is appropriate that Mark and Jen are raising money for the International Wader Study Group and for Project Godwit. As they tweeted about their travels and talked about Black-tailed Godwits at local press events, at different nature reserves, they revealed some of the conservation challenges that waders face.

The RSPB nature reserve at Titchwell (North Norfolk) is a favourite pit-stop for Project Godwit birds. These three youngsters, all head-started in 2018, visited before flying south.

Project Godwit is not just about head-starting more Black-tailed Godwit chicks. The team is trying to improve the chances for nesting birds out on the Washes, using electric fences and other predation reduction schemes, and through the development of alternative breeding areas that are under less threat of flooding during spring and summer deluges.

Within Britain and when they head south through Europe and into Africa, Black-tailed Godwits are dependent upon a network of sites. Some of them are fully-protected nature reserves, others have been given international recognition as SPAs and Ramsar sites, but there are many other locations that are important but not designated. Sightings of Project Godwit birds and locations downloaded from geolocators will help to identify areas in which birds may be vulnerable to habitat change and new developments.

A new airport that is planned for the Tagus Estuary is a huge threat to limosa Black-tailed Godwits that breed in Western Europe, including the small English population. It’s thought that about half of the Project Godwit birds use the rice fields and mudflats of the Tagus Estuary, as you can read in Black-tailed Godwits are on their way home. As mentioned above, Nelson has been seen in the Tagus Estuary on several occasions (see map alongside). The proposed airport threatens many species of migrant waterbirds (Tagus Estuary: for birds or planes).

An important unknown when trying to conserve our larger wader species is ‘what happens to the teenagers?’. When do species such as Black-tailed Godwits start to breed and what do they do in the period between fledging and breeding? A key part of Project Godwit is to mark chicks in the wild, as well as head-started birds, hopefully answering questions such as ‘what proportion breed in their first year?’ and ‘where do immature birds spend the pre-breeding years’? Perhaps the International wader Study Group will be able to support similar work for other large shorebird species, through its small project grants?

Support for Mark and Jen

This epic sponsored cycle ride is funding work by Project Godwit and the IWSG. It was a great opportunity to thank colour-ring readers who have reported marked birds, to emphasise the importance of protecting networks of sites for migrant waders, and to highlight some of the conservation challenges that lie ahead.

If you would like to help Mark and Jen to support International Wader Study Group Small Projects Grants, please donate here: https://www.waderstudygroup.org/donate/

If you would like to help Mark and Jen to support the RSPB’s contribution to Project Godwit please donate here: https://www.justgiving.com/fundraising/fundsforwaders


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.

Is the Curlew really ‘near-threatened’?

If a Curlew can live for over 32 years and there are flocks of 1000 in Norfolk, how can they be described as near-threatened? 

Dark times lie ahead for Curlew? (© Graham Catley)

Dark times lie ahead for Curlew? (© Graham Catley)

Thirty years ago there were eight members of the world-wide curlew family but now we may well be down to six.  The planet has lost one species, the Eskimo Curlew, with no verified sightings since the 1980s, and probably the Slender-billed Curlew as well.  Of the others, Far Eastern Curlew and Bristle-thighed Curlew are deemed to be endangered and vulnerable, respectively, and our own Curlews are classed as near-threatened, which is the next level of concern. This may seem strange, especially when flocks of 1000 can be seen on the Norfolk coast.  However, evidence suggests that we should take heed of what is happening to other members of the curlew family, as we consider the future of this evocative species with its wonderful bubbling curl-ew calls.

Threat levels for the eight members of the Curlew family (based on IUCN BirdLife assessments)

Threat levels for the eight members of the Curlew family (based on IUCN/BirdLife assessments)

Our Curlew – more properly called the Eurasian Curlew – was until relatively recently a locally popular game species in Britain, especially in September and October, when birds are reputed to be particularly flavoursome.  A male Curlew is equivalent in weight to a Wigeon (or two Teal) and the bigger female may well be as heavy as a Mallard, so it is not surprising that they were worth targeting.  They came off the British quarry list in 1981.

Map showing movements of ringed curlews. Purple dots indicate where British/Irish ringed birds have been recovered and orange dots show ringing sites of birds found here and wearing foreign rings. Maps of movements can be found on the BTO website at http://www.bto.org/volunteer-surveys/ringing/publications/online-ringing-reports

Purple dots indicate where British/Irish ringed Curlews have been recovered and orange dots show ringing sites of birds found here and wearing foreign rings. Maps of movements can be found at http://www.bto.org/volunteer-surveys/ringing/publications/online-ringing-reports

The Curlews that we see on the Norfolk coast in autumn and winter are drawn from a wide breeding area; some are of British origin but many are from Scandinavia, Finland and Russia.  The Wash Wader Ringing Group recently received a report of a bird that was ringed in Norfolk in September 2000 and recovered in Izhma in Russia in May 2014.  At 3300 km (2000 miles) this is nearly as far away as the furthest east dot on the map of Curlew recoveries, shown here and published on the website of the British Trust for Ornithology.  The bird was an adult when ringed so must have been at least 15 years old when shot.  This seems like a good age for a Curlew but is less than half of the British longevity record, set by a chick ringed in Lancashire in 1978 and found dead on the Wirral in 2011.

Curlew mortality is higher in severe winters (© Graham Catley)

Curlew mortality is higher in severe winters (© Graham Catley)

Curlew numbers on the Wash, which sits between the counties of Norfolk and Lincolnshire, increased dramatically when shooting ceased in 1981, although milder winters could have also have been influential.  In the five years immediately before the ban, the average maximum, winter Wetland Bird Survey count on the Wash was 3281, rising to 9642 in the period 2006/07 to 2010/11.  There were similar increases on the North Norfolk coast and a bit further south at Breydon Water.  The broader, national picture is one of increase between 1981 and 2001, although generally at a lower level to that seen in Norfolk, followed by a steady, shallow decline.  If numbers are higher than they once were does this mean that we should be less concerned about Curlews – and what is the justification of the species’ near-threatened designation?

Curlews fly vast distances to spend the winter on the estuaries of Britain & Ireland (© Graham Catley)

Curlews fly vast distances to spend the winter on the estuaries of Britain & Ireland (© Graham Catley)

Conserving migratory species is difficult because individuals rely on different resources in different countries at different stages of the year.  For Curlews, there is evidence that breeding season problems are at the heart of large decreases in numbers in Russia, through the Baltic and into The Netherlands – the countries from which much of the wintering population on the east coast is drawn.  According to the European Commission’s species management plan, drivers of decline include wide-scale intensification of grassland management for milk production, land-abandonment and increased predation in some areas.  Autumn, winter and spring hunting is thought to have had a lesser but contributory effect to the long-term losses, with hunters across the European Community shooting between 3% and 4% of the population each year.  In the last twenty years, within the EC, hunting of Curlew has been confined to Ireland, Northern Ireland and France.  Much of this shooting pressure was and is in France, where coastal hunting of Curlew was reinstated after a five year moratorium. Read blog about this here.

curlew webpageFocusing on Britain and Ireland, we have seen major losses in our breeding populations.  In Ireland, the Curlew population is estimated to have dropped from 5000 to 200 pairs in the twenty years between 1991 and 2011 (with further declines since – see Ireland’s Curlew Crisis blog below). There has been an 80% decline in Wales and other losses elsewhere.  There’s more about these distributional changes in a 2012 article written for the BTO website.

Curlew productivity in several areas appears to be very low and it is possible that the adults we are seeing are part of an ageing population.  As has been shown in seabirds, counts of adults can give a false sense of security, as it is easy not to notice that there is little recruitment of new, breeding adults into the population, with obvious long-term consequences.

Graph shows the changing Curlew population in Great Britain (Wetland Bird Survey)

Graph shows the changing Curlew population in Great Britain (Wetland Bird Survey)

The decline in the number of breeding Curlew in Great Britain is clearly reflected in monthly, winter counts undertaken by volunteers on west coast estuaries.  On the Dee, for instance, the average peak-winter count dropped from 6109 in the early 1970s to 4348 in the five years after the shooting ban, rose to 5081 in the late 1990s but then slipped back to 3802.

In Ireland and Northern Ireland, a total ban on shooting Curlew was announced in 2012, brought in once it was clear that the estimated November harvest of between 6% and 8% was unsustainable and set against a background of the collapse of the local breeding populations.  The same local reasoning lies behind continuing protection in Wales, western England and in much of Scotland, especially at a time when financial support to land-managers is being used to try to bolster British breeding numbers.  In eastern England, Curlew conservation has a more international flavour, as we provide a safe haven for birds from as far away as Russia.

With relatively few continental birds, the Wetland Bird Survey trend reflects more local declines

With relatively few continental birds in Northern Ireland, the Wetland Bird Survey trends probably reflect local declines

Britain & Ireland, between them, provide winter homes for half of the Europe-wide population of Curlews (about 210,000 out of 420,000), with the Netherlands holding 140,000 birds.  There are also significant flocks in Germany and about 20,000 in France.  These may seem like reasonable numbers but, given that fewer chicks are being raised, the number of adults is declining, two close relatives have been driven to extinction and other curlew species are in trouble, the label of near-threatened seems highly appropriate.

We should be proud of our wintering Curlews in Great Britain, where numbers have stabilised, albeit at a level that is 20% lower than at the turn of the century, but there is no room for complacency in Northern Ireland, where the decline continues.

Update: Curlew was added to the red list of the UK’s Birds of Conservation Concern on 3 December 2015

Other WaderTales blogs about Curlew

  • Why are we losing our large waders? takes a look at a review of the common threats faced by the 13 Numeniini species (godwits, curlews and Upland Sandpiper).
  • Curlews can’t wait for a treatment plan focuses on the primary drivers of the species’ breeding decline in Great Britain.
  • Sheep numbers and Welsh Curlew looks at habitat associations within a large site  in the Welsh uplands; getting the grazing regime right seems to be very important.
  • Curlew Moon has at its heart a review of Mary Colwell’s book of the same name but also summarises some of the issues being faced by Curlew in Ireland and the UK.
  • Ireland’s Curlew Crisis focuses on the nationwide breeding survey between 2015 and 2017, which revealed a 96% decline in the number of pairs in just 30 years.
  • Curlews and foxes in East Anglia suggest that ‘curlew plots’ may be helpful in the fight to conserve the species.

On autumn high tides, flocks of Curlew roost on east coast stubble fields (© Graham Catley)

On an autumn high tide, a flock of Curlew roosts on an east coast stubble field (© Graham Catley)


 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

UK Dotterel numbers have fallen by 57%

Research from RSPB Centre for Conservation Science, with University of Aberdeen (School of Biological Sceinces), Scottish Natural Heritage (SNH) and Natural Research Ltd

Male Dotterel brooding chicks: Alistair Baxter

Male Dotterel brooding chicks: Alistair Baxter

I have only once climbed a mountain to count Dotterel, with Phil Whitfield decades ago, but that is enough to appreciate how many hundreds of hours of hard work lie behind the statement, “The number of Dotterel breeding in the UK declined by over half between 1987/88 and 2011”. This is the headline in a paper published in the November 2015 issue of the BTO journal, Bird Study:

Changes in the abundance and distribution of a montane specialist bird, the Dotterel Charadrius morinellus, in the UK over 25 years. Daniel B Hayhow, Steven R Ewing, Alistair Baxter, Andy Douse, Andrew Stanbury, D Philip Whitfield & Mark A Eaton Bird Study 62:4, 443-456

As Des Thompson and Phil Whitfield wrote at the conclusion of their account for the 1988-91 Breeding Atlas, “The Arctic affinities of the British Dotterel, its beauty, its rarity and its likely sensitivity to habitat and climate change secure its place as one of our most fascinating breeding birds”.  Well-documented stories of females laying clutches in Scotland, to be brooded by their male partners, and then flying on to Norway to lay second clutches add an air of mystery too.

The 2011 Dotterel Survey was carried out under the Statutory Conservation Agencies/RSPB Annual Breeding Bird Survey (SCARABBS) programme and was funded by the RSPB and SNH (Alistair Baxter)

The 2011 Dotterel Survey was carried out under the Statutory Conservation Agencies/RSPB Annual Breeding Bird Survey (SCARABBS) programme and was funded by the RSPB and SNH (Photo: Alistair Baxter)

The population estimate of 423 breeding male Dotterel in 2011 represents a decline of 43% since 1999, when the comparable total was 747 pairs, and of 57% since 1987/1988 (981 pairs).  All regions except the West Highlands had lower numbers in 2011 than in 1999, with the core area of the East Highlands (the Grampians east of the A9) experiencing a significant decrease of 32% since 1999 and 56% since 1987.  This massif has become increasingly important, with 60% of the pairs in what amounts to 30% of the potential breeding habitat for Scottish Dotterel.

No Dotterel were recorded outwith Scotland during the systematic national survey but Bird Atlas 2007-11 fieldwork did add a record from Northern England.  In the absence of annual monitoring, a national survey can only provide a snapshot for a species.  However, information gathered during the four summers of the Bird Atlas project and as part of an ongoing detailed study suggests that the results for 2011 are representative of the current UK Dotterel population – and that the declines are therefore very much real.

Population changes across the range

Large-scale surveys of Dotterel are difficult, due to the remoteness of many of their breeding sites, and monitoring elsewhere across their European breeding range tends to be based on visits to particular sites or using transects.  Given the plasticity shown by the females – including an ability to nest in two countries in one year – changes in apparent numbers could potentially reflect the fact that birds breed further north in some springs than in others.  The best series of data come from Swedish Lapland, where Svensson & Anderson reported no changes in the population over the period 1972 to 2011.

In, Finland, Pulliainen & Saari observed that most females left their study area after egg-laying and hypothesised that this was in order to secure more mates further north. Lucker et al. have found evidence for higher rates of shared incubation by females at the more northern extent of the species’ breeding range than those breeding further south, providing some evidence to support this hypothesis.  Saari had previously estimated the Finnish population to be 90% less than in the early 1900s and suggested that hunting in early 20th century and overgrazing by reindeer may have been to blame.   Since the 1960s, the tree line has advanced and large areas of the mountain heath are now covered by scattered Scots Pines, making the habitat largely unsuitable for Dotterel.  Similar processes, associated with warmer conditions, could have major, negative impacts the number of Dotterel breeding in Scotland.

Is the SPA network working for Dotterel in Scotland?

Racomotrium heath is an important and increasingly rare habitat (Alistair Baxter)

Racomotrium heath is an important and increasingly rare habitat (Alistair Baxter)

The designation of Special Protected Areas (SPA), based on the results of the 1987/88 survey has been a key tool in the efforts to conserve Dotterels in Scotland.  This network of montane sites has helped to provide a focus for research funding and planning considerations.  Encouragingly, SPAs have supported between 50% and 60% of the population since designation.

The decline in numbers of Dotterel within and outwith the SPA network is of concern, but in terms of site occupancy, sites in SPA/SSSIs were more likely to be occupied than those outside the protected area network.  Protected area designation has been shown to be good for a group of northern species at the trailing edge of their distribution in the UK, although this effect decreased at higher latitudes and altitudes (Gillingham et al. 2015).

Explaining the declines

The well-referenced, discussion section of the paper looks at the potential reasons for the changes to Dotterel populations and assesses the available evidence.

Habitat change in the high mountains: Racomitrium moss heath has been shown to provide important foraging opportunities for Dotterel of all ages; this is a habitat that has been in a long-term decline over the last half century.   Studies have outlined how overgrazing and levels of atmospheric nitrogen interact, resulting in changes to the composition and extent of montane heaths.

A frequent prey of both adult and juvenile Dotterel is Tipulid (cranefly) larvae which require dense mats of moss vegetation.  Changes in composition and extent of Racomitrium heath could result in reduced prey availability, potentially affecting settlement decisions and breeding success for Dotterel.

Raven abundance has increased across much of the Dotterel's range (Map from Bird Atlas 2007–11, which is a joint project between BTO, BirdWatch Ireland and the Scottish Ornithologists’ Club)

Raven abundance has increased across much of the Dotterel’s range (Map from Bird Atlas 2007–11, which is a joint project between BTO, BirdWatch Ireland and the Scottish Ornithologists’ Club)

Predation in the breeding season: Predation of Dotterel eggs by Ravens can cause localised declines, and lower return rates have been reported for adult male Dotterel after clutch loss by predation. The period of decline in Dotterel is coincident with an increase in range and abundance, of Ravens in Scotland.  Although previous work has found no significant negative associations between Raven numbers and upland wader populations, this interaction may well warrant further investigation.

Disturbance: There is little strong evidence for widespread effects of increased visitor numbers, despite negative impacts of such activities on heath condition.

Pressures in wintering areas: Pesticide use and hunting on the wintering grounds, North Africa and Spain, have been suggested as possible factors in the decline.

More attractive conditions further north: Upland species, such as Dotterel, are cold-adapted and may well find northerly areas more conducive to breeding.  Without a flyway approach to Dotterel monitoring it is not possible to distinguish between a northerly shift in the breeding area of Dotterel and population-scale declines.

What next?

The 2011 Dotterel survey clearly shows the decline in numbers of Dotterel breeding in the UK and contraction to core sites in the East and Central Highlands.  Further, detailed work is required to understand the mechanisms driving the observed population trends, which may well involve studies in wintering areas and migration hot-spots, as well as a mixture of ecological research and ongoing monitoring in the mountains of Scotland.

The 2011 Dotterel survey has provided a spring-board for detailed research by Alistair Baxter, which is being written up as part of his PhD at the University of Aberdeen.  By repeating studies carried out during the 1980s by SNH, he hopes to see whether changes in habitat availability, habitat quality and invertebrate abundance can help to explain the decline in numbers in the last thirty or so years.

Ptarmigan is another montane species that will be targeted by

Ptarmigan is a key montane species that is being targeted by “What’s Up?” (Alistair Baxter)

Given how much effort has to go into any survey of upland species and the relative infrequency of national surveys, it is great that two recent initiatives are making the most of the calories burned to climb our highest peaks.  Many volunteers involved in the annual Breeding Bird Survey of upland squares now add an adjacent square to the original, randomly-selected plots, in order to increase the sample size in these sparsely populated but special bird areas.  Another valuable contribution is being made by mountain-lovers who know their birds and who are now contributing to the BTO Scotland led “What’s Up?” project.  This focuses on species that are sensitive to climate change and disturbance, such as Ptarmigan, Snow Bunting and Dotterel.

In an era of ever tightening budgets, it is unclear when it might be possible to organise another national survey for Dotterel.  Let’s hope that, until then, “What’s Up?” can help to alert us to distribution changes and that annual surveys of key sites might provide indications of national population changes. 

Dotterel was moved onto the red list of species of conservation concern on 3 December 2015.


 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

Conserving British-breeding Woodcock

To help to take the pressure off declining and now red-listed British-breeding Woodcock, many estates are already delaying the start of the Woodcock shooting season.  How might this make a difference?

This is a modified version of an article published in Shooting Times on 30 Sep 2015. There are updates at the end, reflecting changing advice provided by the Game & Wildlife Conservation Trust.

Photo: Richard Chandler

Photo: Richard Chandler

Each autumn, the British population of Woodcocks is swamped by the arrival of up to a million birds, returning from northern Europe and Scandinavia. The exact timing of their migration is very much influenced by weather, with birds crossing the North Sea as early as October or as late as December.  The numbers each year are thought to vary markedly, reflecting peaks and troughs in the size of the European breeding population, annual chick production, the amount of frost and snow on the other side of the North Sea and the timing of periods of cold weather.

A quick look at the bag index for Woodcock, produced by the Game & Wildlife Conservation Trust (GWCT), shows annual variation in the numbers shot each winter but no downwards trend.  Hunting appears to be sustainable (but see note at the bottom giving advice from GWCT about shooting in winter of 2017/18).  Unfortunately, there is a problem; British-breeding Woodcock are in serious decline and there is no way to differentiate between a local bird and one from continental Europe.  As the GWCT Woodcock tracking project has shown, birds share the same woodland habitats during winter months.  Mara and Jack, for instance, two birds caught in March 2014 on Islay, have very different annual stories to tell, with Mara breeding locally and Jack migrating to Russia.

A shrinking distribution

Bird Atlas 2007-11, published by the British Trust for Ornithology (BTO), confirmed that our Woodcock are in trouble.  Between 1968-72 and 1988-91, the number of 10×10 km atlas squares where Woodcock were present fell from 1439 to 917, representing a decline of 36%.  By 2008-11, the number was down to 632, a further drop of 31%.  In the 1968-72 Atlas, Woodcocks were generally widespread, with birds absent only from parts of southwest England and Wales and easy to find from the North Midlands through to northern Scotland, other than in the highest mountains.  Fragmentation that was becoming apparent in 1988-91 was glaringly obvious in 2008-11, especially in the south and west.  In Ireland the situation, if anything, looked worse.

Bird Atlas 2007-11, published by the BTO, in association with the Scottish Ornithologists’ Club and BirdWatch Ireland, shows that breeding Woodcock are disappearing from southern and western Britain, as well as from Ireland. Downwards pointing black arrows show losses, with bigger symbols indicating recent changes.

Bird Atlas 2007-11, published by the BTO, in association with the Scottish Ornithologists’ Club and BirdWatch Ireland, shows that breeding Woodcock are disappearing from southern and western Britain, as well as from Ireland. Downwards pointing black arrows show losses.

Early results being contributed to the Bird Atlas 2007-11 project confirmed that there was an urgent need for a special Woodcock survey, to try to assess numbers as well as distribution, and this was organised for the summer of 2013.  The GWCT and the BTO wanted to replicate the survey they had organised in 2003, which suggested that the breeding population across Scotland, Wales and England included just over 78,000 territorial males.

Andrew Hoodless of GWCT has shown that the number of Woodcocks observed during a standard evening watch period provides a good index of local abundance.  The national survey called for the deployment of hundreds of birdwatchers, who were asked to visit chosen sites, many of which had been visited ten years previously.  Standing at dusk and listening to the distinctive roding calls of male Woodcocks, as they patrol the boundaries of their territories, provides magical moments for lucky birdwatchers.  However, the chance of success in many parts of the country was far lower in 2013 than it had been in 2003.  A paper, with a full regional analysis was published in 2015, revealing an estimated fall in numbers of 30%, to just over 55,000 roding males.  As suggested by the Atlas distribution maps, percentage losses were higher in Wales and England than in Scotland.

Current status and recent trend of the Eurasian Woodcock Scolopax rusticola as a breeding bird in Britain, by Christopher J Heward, Andrew N Hoodless, Greg J Conway, Simon Gillings & Robert J Fuller, in Bird Study Nov 2015

The main aim of the 2013 Woodcock survey was to assess the population, rather than to understand the causes of decline, but it is interesting to note that there were smaller losses in the largest areas of woodland.  More detailed studies have suggested that larger woods may offer a greater diversity of habitats and damper micro-climates in which to feed.  Booming deer populations are having major effects on a lot of woodlands; by browsing the vegetation they can open up the understorey, thereby removing nesting habitat and drying out soils.  There are probably several factors driving down the breeding population and it has been suggested that recreational disturbance and over-winter hunting of resident birds could each be playing a part in declines.

Changes to the hunting season?

BirdTrack is coordinated by the BTO, in partnership with RSPB, BirdWatch Ireland, the Scottish Ornithologists’ Club and the Welsh Ornithological Society. These lists provide fascinating information about the timing of migration, annual breeding patterns and species’ abundance. See www.birdtrack.net to learn more.

BirdTrack is coordinated by the BTO, in partnership with RSPB, BirdWatch Ireland, the Scottish Ornithologists’ Club and the Welsh Ornithological Society. These lists provide fascinating information about the timing of migration, annual breeding patterns and species’ abundance. See www.birdtrack.net to learn more.

Although the main pressures may well occur during the summer months, one way to help British breeding Woodcock may be to change the start of the shooting season.  The season currently opens on 1 September in Scotland and 1 October across the rest of the UK.

Looking at BirdTrack data, collected from species lists sent in by thousands of birdwatchers across Britain & Ireland, it is clear that there are virtually no continental Woodcock in these islands during September and few until at least the second half of October.  In the graph alongside, the red line shows average rates of occurrence on birdwatchers’ lists.  The blue line for 2014 indicated a pulse of arrivals in early October, largely as observed by birdwatchers on the east coast.  These birds will have moved inland and disappeared into woodland and farmland.  The main arrival in this particular year appears to have been in late October with later spikes in the graph suggesting further bursts of east coast activity in November and December.

The 2013 Woodcock survey was funded by the Game & Wildlife Conservation Trust, the Shooting Times Woodcock Club and a charitable trust. Photo: Richard Chandler

The 2013 Woodcock survey was funded by the Game & Wildlife Conservation Trust, the Shooting Times Woodcock Club and a charitable trust. Photo: Richard Chandler

The BirdTrack pattern will come as little surprise to gamekeepers and shoot-owners, many of whom already restrict Woodcock shooting to the winter months, in order to minimise losses of local, resident birds.  GWCT scientists have been encouraging restraint in the autumn months for some while.  Now, having analysed the results of the GWCT/BTO 2013 Woodcock survey, and shown a further decline of nearly a third in just ten years, they are researching the potential impact of shooting on resident birds. This will include an assessment of whether a formal change to the timing of the hunting season for Woodcock is required, in order to add an extra level of protection to resident birds.

Update: 28 July 2017

New GWCT  guidance: ‘generally we recommend not shooting woodcock before 1 December’ and not at all if ‘numbers have been low in the area’. More information is available at https://www.gwct.org.uk/media/696047/Pocket-woodcock-guide.pdf

Update: 11 December 2017

Migrant Woodcock appear to have had a poor breeding season and GWCT is advising restraint:

Dr Hoodless has issued the following statement: “GWCT and the Woodcock Network are advising shooters across the UK to rethink their woodcock shooting for this season and reduce their bags. This echoes moves being taken by organisations in several other European countries. A further update will be issued in early January, once more information is available.”

“Although similar events will have happened many times in the past, this is the first time that monitoring of woodcock age ratios by ringers, and improved communication across Europe, has been able to offer shooters an early warning system. Populations normally rebound after such events, but most shooters understand the importance of preserving breeding stocks when there are signs of adverse natural events and are prepared to minimize shooting pressure in order to aid population recovery.”

Read more here

Update: 16 March 2018

Woodcocks are severely affected by cold weather. Research by GWCT suggest that Woodcock start to suffer when the ground has been frozen for relatively short periods of time. They propose restraint after four days of freezing conditions, with birds being given a recovery period of seven days once a thaw commences. There’s more in this blog here and the paper can be found here.

Update: September 2020

There is no suggestion that the numbers of Woodcock breeding in Finland, Sweden and Norway are changing. This blog summarises survey data for breeding waders during the period 2006 to 2018.


 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 helping hand for Lapwings

This article has been slightly adapted from one written for the Autumn 2015 edition of The Harrier, published by the Suffolk Ornithologists’ Group

Lapwing in flight: Richard Chandler

Lapwing in flight: Richard Chandler

The space-invader cries of displaying Lapwings are welcome signs of spring across much of Britain’s countryside and losses of this iconic species, especially in lowland England, have been well chronicled.  Conservation organisations, and the RSPB in particular, are successfully supporting breeding numbers on nature reserves but how can their interventions be replicated on working farms, without flooding fields and installing fox-proof electric fences?

On the look-out: Grahame Madge/RSPB impages

On the look-out: Grahame Madge/RSPB impages

Dr Jen Smart of the RSPB Centre for Conservation Science and Professor Jenny  Gill of the University of East Anglia have been studying breeding waders on  RSPB Reserves in the Norfolk Broads for over ten years, but more recently they have extended their wader research into commercially managed grasslands across Norfolk and Suffolk, using funding from Defra.  At the February 2015 ‘Foxycology’ conference, Dr Smart explained how the RSPB is trying to manage the conflict between the conservation of ground-nesting birds and foxes.  The RSPB does not rule out shooting as a protection measure – there’s active fox control in the study site – but prefers to adopt non-lethal solutions to the predation problem.  One answer may be to provide foxes with ‘convenience food’, in the form of mice and voles.  If it’s easier to find mice and voles than wader nests and chicks then perhaps that’s what foxes will do?

Predation is a natural process but rates can be severely skewed by the way that the countryside is managed, especially when the balance of predator and prey is disturbed.  Many predators are opportunists, with species such as foxes, crows, gulls and raptors switching their activities to take advantage of local food availability.  Seasonal abundance of food resources can affect both survival and productivity.  An inexperienced young fox must have a better chance of surviving the winter if he is presented with a generous supply of released pheasants, whilst a vixen, trying to raise a litter of cubs, will find easy pickings in a gull colony.  In the same way, a nature reserve that is full of nesting waders will often attract foxes during the breeding season.

By creating shallow ditches, which add water and insects to grassland habitats, Lapwing productivity is increased: Mike Page/RSPB

By creating shallow ditches, which add water and insects to grassland habitats, Lapwing productivity is increased: Mike Page/RSPB

The RSPB has become very good at increasing populations of wading birds breeding on their lowland nature reserves but staff are frequently frustrated by the low numbers of young birds that survive through to fledging in some years.  Adding water to the landscape, in the form of pools and ditches, attracts high densities of breeding waders, as these wet features provide insect-rich places to which adults can take their chicks.  The RSPB/UEA research team has found that Lapwing nests are far more successful when birds nest at high densities, presumably because they work together to look out for and drive off potential predators, and they also found that Redshanks benefit from the activities of the more numerous and defensive Lapwings.  Practical actions, such as clearing woodland that abuts wetland or removing single trees in which crows sit to spot the next meal, have been shown to reduce avian predation in the daytime, to such an extent, in fact, that three-quarters of nest-losses are now taking place at night.

Lapwing chick: Richard Chandler

A young and vulnerable Lapwing chick: Richard Chandler

Using cameras, the team has shown that 70% of the culprits filmed taking eggs are foxes, with badgers coming a distant second, at 12%.  Wader chicks leave the nest soon after hatching, and RSPB research has shown that chick predation is then largely from foxes at night and raptors in the daytime, but with stoats, weasels and opportunistic birds, such as grey herons, taking smaller numbers.  Overall, by far the biggest threat to productivity is the fox.

One fox (and badger) deterrent that is available on nature reserves is to use well-maintained mains-supplied electric fences to surround fields in which waders nest.  Trials by the RSPB have shown that Lapwing fledging success is significantly improved in fenced areas, increasing from just over 0.2 chicks per pair to 0.8 chicks.  The target level for a sustainable population is 0.6 young per pair so the lower figure is well below par and 0.8 should be providing a surplus of birds that can go on to nest elsewhere.  Fences are not perfect, however; they do not exclude predators such as stoats and weasels, and the increased success of nests means high densities of chicks can be an irresistible resource for opportunistic and adaptable aerial predators trying to feed their own young.  Fencing is also only really effective on a relatively small scale so does not provide the solution to what is a landscape-scale problem.  RSPB research has shown that there is a lot of variability in predation rates, which provides opportunities to try to understand the complex interactions between foxes, mustelids (stoats and weasels), small mammals and waders.

In open grassland, Lapwings can keep an eye out for approaching predators: Richard Chandler

In open grassland, Lapwings can keep an eye out for approaching predators: Richard Chandler

Much of the patchiness of productivity within a site is linked to the amount of grass in fields and along field edges.  Grazing is a key management tool in wet grasslands, with cattle creating the short and varied sward structure that is attractive to a range of breeding waders.  By using ink tracking tunnels, within which mammals leave their footprints, and looking for field-signs of activity, Dr Becky Laidlaw has been able to show that this short grass is of little use to mice and voles.  She discovered that they prefer verge areas, outside the fields, where the grass is at least 20 cm tall and where there is ground-level vegetation cover of more than 80%.  Using data on wader nest success collected over 10 years, she was also able to show that Lapwings nesting in fields close to this small mammal habitat had lower rates of predation. Adding in tall grass strips and patches within a farmland landscape could potentially increase the populations of small mammals, thereby distracting foxes and mustelids, and reducing predation pressure.  Avian predators of wader chicks might appreciate this intervention too!  This work is published as:

The influence of landscape features on nest predation rates of grassland-breeding waders by Rebecca A Laidlaw, Jennifer Smart, Mark A Smart & Jennifer A Gill in Ibis 157:4 Oct 2015

Over the last two years, the RSPB/UEA team has worked with landowners of commercial grasslands across East Anglia, who between them are responsible for a large percentage of remaining breeding wader populations. Building on the work on reserves, the aim was to understand whether habitat suitability and predation processes differ between reserve and wider countryside waders.  To accomplish this, they assessed the extent to which grassland management options within agri-environment schemes support small mammal populations, as well as measuring field wetness, Lapwing densities and nest predation rates.  They also assessed the importance of different nest predators for waders nesting in the wider countryside and within nature reserves.

A weasel leaves its mark: Becky Laidlaw

A weasel leaves its mark: Becky Laidlaw

Becky and her team found similar distributions of small mammals in the wider countryside as had already been found on nature reserves.  Within both, there were higher densities of small mammals within grassland habitats outside of fields, while presence within fields did not vary significantly among fields managed under different grassland agri-environment options.  Encouragingly, densities of Lapwing nesting in fields managed in accordance with the breeding wader option were significantly higher than in fields with no interventions. Lapwings nesting in areas with many other Lapwings and nests that were closer to patches of small mammal habitat were less likely to be predated, but the rate of Lapwing nest predation did not differ between the wider countryside and reserves.  It should be possible, therefore, to create Lapwing hot-spots outside of nature reserves, thereby expanding the reproductive potential of East Anglia.  Unsurprisingly, given the previous findings about the causes of nest-losses on nature reserves, wider-countryside sites where foxes were present experienced both higher overall nest predation and nocturnal nest predation.

Redshank also benefit for management designed to support Lapwings and probably appreciate the shared look-out duties Photo: Richard Chandler

Redshank also benefit for management designed to support Lapwings and probably appreciate the shared look-out duties Photo: Richard Chandler

The main findings of this study are that wader nest predation rates and spatial patterns of nest predation on lowland wet grasslands are remarkably similar inside and outside reserves. This should help to directly inform the design and development of lowland wet grassland landscapes, making them capable of attracting and supporting sustainable populations of breeding waders within the constraints of commercial grasslands.  Jen Smart is optimistic; “If we can provide wet fields that look attractive to Lapwings in spring and patches of tall vegetation that hold high numbers of small mammals it ought to be possible to improve nesting success and productivity”.  She and her colleagues are now looking at how a range of different agri-environment options might be used to create such landscapes.  The next phase of the project will be to try out the most promising options, in order to see the scale at which these patches of tall vegetation for small mammals need to be provided if they are to deliver the desired result – more breeding waders.

Update 

The are several other WaderTales blogs that may be of interest to people who like Lapwings:

For a full list of WaderTales blogs visit https://wadertales.wordpress.com/about/

 


 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


Why do some Black-tailed Godwits wear colour-rings?

The birdwatchers at Cley provide daily observations of the colour-ringed Black-tailed Godwits that turn up on the site, revealing some fascinating stories and contributing massively to migration research.

This blog was originally written for the Norfolk Wildlife Trust’s magazine, Tern.

Flock of Black-tailed Godwits at Cley: Pat Wileman

Flock of Black-tailed Godwits at Cley: Pat Wileman

No two visits to Cley are the same; the birds change with the seasons and even from day to day.  If there are 200 Black-tailed Godwits in front of Daukes hide on Tuesday and only 100 on Thursday does that mean that half have moved on – or did all of the earlier birds leave, to be replaced by a new selection?  The fact that several individuals wear colour-rings enables regular godwit observers, such as David and Pat Wileman and Mark Golley, to help provide some answers.

The highest Cley counts of Black-tailed Godwits now occur in the autumn, when birds can be found feeding or roosting on the scrapes and lagoons, pulling worms from the wet meadows or picking up grain from nearby stubble feeds.  Many colour-ringed birds have only been seen once but others become old favourites, like ‘orange/green – orange/green-flag’.  Until 2015 he spent the late summer weeks at Cley moulting out of his red summer plumage (see series of three pictures below).  As autumn turned to winter, he flew onwards to the Tagus Estuary in Portugal, where he was first ringed in 2007 by José Alves, one of a team investigating migration at the Universities of East Anglia, Iceland and Aveiro (Portugal).

Three pictures of the same bird, moulting out of its breeding plumage. Photographs by Chris Cook, Pat Wileman & Richard Chandler

Three pictures of the same bird, moulting out of its breeding finery and into winter plumage. Photographs by Chris Cook, Pat Wileman & Richard Chandler

Another well-watched bird is ‘lime – yellow/black//white’.  She was first caught on the Wash in September 2002 and has spent every March/April at Cley or Stiffkey. She has been seen in Ireland in mid-winter and nests in northern Iceland.  This bird was already an adult when ringed 12 years ago so her exact age is unknown.  The current record for Icelandic Black-tailed Godwits is 25 years but colour-ringing is likely to show that they can live even longer.

The ring on the lower part of the right leg used to be white! This distinctive staining is an extra complication for observers at Cley. Photo: Chris Cook

The ring on the lower part of the right leg used to be white. This distinctive staining is an extra complication for colour-ring observers at Cley. Photo: Chris Cook

Cley is just one observation point across the whole of the Icelandic Black-tailed Godwit’s range.  Jenny Gill, who leads the godwit research at UEA, is working with colleagues in Iceland, Portugal, France, Spain, Ireland and across the UK to understand migration patterns and their consequences for survival and breeding success.  Every reported set of colour-rings is important, even if the same bird was seen in the same spot yesterday.  It may not be there tomorrow, in which case today’s record has helped to pinpoint the departure date.  Visitors at Cley can send their sightings to David at cbcrecords@talktalk.com , write them in the hide log book or contact Jenny at j.gill@uea.ac.uk

Whilst the vast majority of Cley Black-tailed Godwits are of the Icelandic race, a few birds from the small population of birds that breed in the Ouse and Nene Washes also pass through in the autumn. Later they will join thousands of birds from continental Europe, wintering in Iberia and west Africa.  The Icelandic colour-ringed birds are providing fascinating insights into the migratory movements of that subspecies, the numbers of which have risen at the same time as the numbers of the continental subspecies have declined.  Icelandic birds winter all around western Europe; Cley birds have been seen in France, Portugal, Spain and Ireland, as well as around much of the UK.

Colour-ring sightings have helped to reveal a huge amount about Black-tailed Godwits.  Amongst many other findings:

Rates of population increase were greater on estuaries with low initial numbers, and Black-tailed Godwits on these sites had lower prey-intake rates, lower survival rates and arrived later in Iceland than those on sites with stable populations. The Buffer effect and large-scale population regulation in migratory birds. JA Gill, K Norris, TG Gunnarsson, PW Atkinson & WJ Sutherland. Nature 412, 436-438 (26 July 2001).

We know that birds from the same pair have nothing to do with each other outside the breeding season, even wintering in different countries, but that they need to arrive on territory within a day or two of each other if there is not to be a divorce.  Pair Bonds: Arrival synchrony in migratory shorebirds. TG Gunnarsson, JA Gill, T Sigurbjörnsson & WJ Sutherland.  Nature 431, 646 (7 October 2004). There’s a WaderTales blog about this paper.

We have learnt that spring migration is getting earlier, driven by new recruits getting back to Iceland earlier than older birds.  Why is timing of migration advancing when individuals are not? , , , , ,

Want to know more?

This blog tells more stories about individual Black-tailed Godwits and the birdwatchers who study them: Godwits and Godwiteers.

There are many more WaderTales blogs about Black-tailed Godwits. Click here to see what is available. 

Cley is a great place to see godwits at really close quarters, as are a number of other nature reserves around the country.  Reports of colour-ringed birds provide an important element of ongoing migration research.  Please contact Jenny Gill at j.gill@uea.ac.uk and you will receive a life-history of your bird, either from Jenny or from one of her collaborators.


 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

Migratory decisions for Icelandic Oystercatchers

New Oystercatcher research in Iceland aims to explain how migration patterns change over time and how individual behaviour may drive population change

Which Oystercatchers will cross the Atlantic and which will stay in Iceland? (Tómas Gunarsson)

Which Oystercatchers will cross the Atlantic and which will stay in Iceland? (Tómas Gunarsson)

Most waders leave Iceland in the autumn, with vast numbers heading for the British Isles, coastal Europe and even Africa.  Amongst the exceptions are hundreds of Oystercatchers which ‘tough it out’ in wintry conditions, thereby saving themselves two long trans-Atlantic flights and potentially ensuring that they are able to make a prompt start to the next breeding season. Why do some Oystercatchers migrate when others don’t?  Is it the same birds each year?  Do resident birds have a competitive advantage when it comes to choosing a territory and raising chicks, and do these chicks follow the same migratory strategy as their parents?  In an era of changing weather patterns, can birds change their migratory preferences and how does this happen?  These are some of the questions that are being tackled by Verónica Méndez, as she monitors the movements of colour-ringed individuals in a joint University of East Anglia (UK) / University of Iceland / University of Aveiro (Portugal) project.

Migration in a changing world

Throughout the world, the distribution, abundance and behaviour of species is changing, partially as a response to climatic change. Given that most bird protection relies on a legislative framework that is site-based, changes to bird distributions are going to make life challenging for conservationists.  Will today’s Special Protection Areas be fit for purpose in 20 years’ time?  As they look to the future, conservationists want to be able to set up a network of sites that can flexibly support migratory species, and this entails understanding why and how migratory patterns are changing and might change in the future.  Icelandic Oystercatchers may well provide an ideal model species through which scientists can learn how migratory decisions can influence individual fitness, population demography and species distribution.

“I’m sure that I started a nest scrape somewhere here”. Spring conditions in 2015 were distinctly wintry: Verónica Méndez

There are likely to be different pressures facing resident and migratory Oystercatchers.  Two birds that breed on adjacent territories might have completely different annual cycles.  The bird that spends the winter in Iceland will not have to migrate but its probability of survival may be reduced by harsher winter conditions, possibly with a more limited set of feeding options and certainly with shorter periods of daylight.  In mid-winter, there is 6hr 40 min between first light and dusk in Reykjavik but 9 hours in Bangor, North Wales.  Come the spring, however, the same bird will be well placed to take advantage if spring comes early, whilst his migratory neighbour will face a hazardous sea-crossing, perhaps being delayed by a fortnight or more if strong northerly winds set in.

Individuals matter

An adult Oystercatcher providing food for a growing chick (Tómas Gunnarsson)

An adult Oystercatcher providing food for a growing chick: Tómas Gunnarsson

Although patterns of change in migratory strategies can be detected by looking at timings of first arrival and counting flocks, these changes can only be explained if we understand what individuals are doing.  It will be interesting to see, for instance, if Icelandic-winterers pair up together and what their offspring subsequently do in their first autumn.  Oystercatchers look after their chicks for longer than most waders so perhaps youngsters will be more likely to adopt the strategy of their parents than other species?

To answer these and many other questions, Verónica and colleagues from the Universities of East Anglia, Iceland and Aveiro have been colour-ringing Oystercatcher adults and chicks on the breeding grounds between the north-west and southern lowlands of Iceland.  Both adults and chicks (when big enough) are ringed with two colour rings on the left tarsus and a flag above another colour ring on the right tarsus (metal ring goes on either tibia and is not part of the scheme).  See update below to learn about a second scheme.

Wintering flocks of Oystercatchers will be checked in Iceland but most of the colour-ringed birds are likely to have flown south.  The team therefore need birdwatchers around the British Isles and along the Atlantic coast of Europe to look out for these marked Oystercatchers and to report them to icelandwader@gmail.com

Catching adult Oystercatchers

The study season for an Oystercatcher fieldworker starts in April, when the first nests start to appear.  Once a full clutch of between 1 and 4 eggs has been produced, both parent birds take turns to incubate for between 3 and 4 weeks.  During this period it is possible to catch the adults by temporarily replacing the eggs with plastic eggs and setting a spring trap or walk-in trap over the nest.  Sometimes the second adult can be caught while the first bird is being ringed, as he or she settles down on the unattended eggs.

Juvenile wearing new colour rings: Verónica Méndez

Juvenile wearing new colour-rings: Verónica Méndez

Catching chicks is harder.  Although they can be metal-ringed at an early age, their legs are too short at this stage for additional colour-rings.  By the time that the youngsters are big enough they can run very quickly – or even fly – providing excellent entertainment for the ‘spotter’ in the research team, as the ‘chaser’ is often outwitted and out-run.

What has been learnt so far?

The first adult Oystercatchers were colour-marked in the summer of 2012 and more were ringed in 2013 and 2014.  In the winter of 2014-15, eight migratory individuals were seen in Ireland, Northern Ireland, Wales, Scotland and Shetland and five resident birds were shown to have stayed in Iceland. Additionally, five birds wearing BTO rings that they acquired in Ireland and Wales have been recruited to the colour-ring project, increasing the sample of known migrants.  By the end of 2015, over 200 adults had been colour-ringed, as well as about 100 new chicks, so there should be plenty of birds to look for this winter.

Breeding adult Oystercatcher: Tómas Gunnarsson

Breeding adult Oystercatcher: Tómas Gunnarsson

A century or more of metal-ringing has shown that Icelandic Oystercatchers migrate mostly to the British Isles and West coast of France, but some have been recovered in Germany, The Netherlands, Spain and Portugal, so please check out any Oystercatcher flocks you see in any of these countries.  Although most observations of colour-ringed Oystercatchers will be made during the winter months, young birds may well be spotted in the summer, as Oystercatchers do not start to breed until they are two or more years old.  If some juveniles winter in Iceland perhaps they might be able to breed at a younger age than their migratory cousins?  That would be yet another way for a change in strategy to not only impact on the fitness of the individual but also on the population demography and the overall migratory strategy of the species.

Oystercatchers are also being ringed with two letter engraved rings, along with two colour-rings: Photo Tómas Gunnarsson

Oystercatchers are also being ringed with two letter engraved rings, along with two colour-rings: Photo Tómas Gunnarsson

An update…

Oystercatchers caught in later catches have been ringed with white, grey or green engraved rings, alongside two colour-rings.  If you come across a bird with a yellow engraved ring then it is probably from a project in Dublin Bay.

When researchers from the two projects got together at the 2015 International Wader Study Group Conference in Iceland they realised that five more Dublin Bay birds could be added to the list of Icelandic breeders that are definite migrants.

Please check flocks of Oystercatchers and report any sightings to icelandwader@gmail.com

Photo: Tómas Gunnarsson

Photo: Tómas Gunnarsson


 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

How volcanic eruptions help waders

Areas of Iceland that have experienced high volcanic ash deposition can accommodate up to three times as many breeding waders.

cropped-2-eldgos.jpg

When Tómas Gunarsson began his PhD at the University of East Anglia on breeding Black-tailed Godwits, supervised by Bill Sutherland and Jenny Gill, little was known about the broad-scale patterns of abundance of waders across Iceland.  As a whole, the country is a haven for breeding waders but what breeds where and why?  In the summer of 2001, Tómas, Jenny and I set off by car to collect data on the distribution and abundance of waders and other bird species within lowland Iceland, continuing this Large Scale Survey during the next two summers.  Having surveyed 764 locations across the lowlands of Iceland, we found a great deal of variation in abundance, some of which was explained by local habitat conditions which we described in Large-scale habitat associations of birds in lowland Iceland: Implications for conservation (Biological Conservation 128 (2006) 265 – 275)

However, there remained a large amount of unexplained difference in wader abundance. Some of this variation appeared to be ‘regional’, as abundances tended to be consistently higher or lower in particular parts of the country, but the cause of these regional differences was not clear.

Fast forward to 2010, when we had the great fortune to be present when Eyjafjallajökull, the famous volcano that halted air traffic across Europe, erupted. As the volcanic ash blew south, disrupting flights and dusting parked cars back in the UK, we thought more about the possible effects of periods of ash deposition within Iceland.  Dust deposition became a hot topic for discussion at the University of Iceland, where Tómas was now Director of the South Iceland Research Centre, especially the effects of ash deposits on soil composition and productivity.  A map of historical dust inputs produced by Ólafur Arnalds, a soil scientist at the Agricultural University of Iceland, showed a pattern that looked very familiar to Tómas.  By collaborating with Ólafur and looking again at the Large Scale Survey data, much of the regional aspect of wader distribution could now be explained.  This work was published as Ecosystem recharge by volcanic dust drives broad-scale variation in bird abundance (Ecology and Evolution 5:12 (2015) 2386-2396)

Survey points for the large scale survey are shown as open circles. Reproduced from Gunnarsson et al 2015.

Survey points for the large scale survey are shown as open circles. Reproduced from Gunnarsson et al 2015.

Dust and birds

It turns out that the regional variation in wader abundance in Iceland is closely associated with volcanic dust deposition, which varies greatly around Iceland because of the active volcanic zone that runs diagonally NE to SW, where the North American and European tectonic plates meet. Areas with high dust input support more waders, probably because of the boost to productivity provided by the high levels of nutrient input. Interestingly, this pattern is most apparent in wetlands (which would be expected as high water levels facilitate nutrient deposition) and is not apparent in agricultural land (probably because more recent fertiliser inputs mask the effects of dust).

Volcanic dust deposition has been linked to primary productivity (vegetation growth) but this is the first study we know of to show links all the way to the top of the food chain.  Iceland may show underlying links between geology and biology more strongly than other countries, where landscapes have been managed more intensively and for much longer than here.

Volcanic dust in Iceland is primarily basaltic and subject to rapid weathering, releasing minerals that are important for ecosystem functions in terrestrial systems.  The fertility of the basaltic volcanogenic dust and rapid deposition rates override the importance of organic matter and clay when it comes to the redistribution of nutrients, through nutrient cycling and buffering of soil and pH.  This can in turn affect invertebrate food resources of birds.

Although volcanoes are the primary producers of dust, distribution is not restricted to active volcanic episodes.  Iceland’s thin soils are readily eroded during windy weather, allowing redistribution of nutrients, and dust trapped in snow and glaciers is released during the spring and summer melt.  As glaciers retreat, the net amount of available ash increases.  Major events such as the eruption of Eyjafjallajökull in 2010 have the potential to significantly add to nutrient levels, although much of the 250,000,000 cubic metres released blew south in this case, with huge consequences for air travel.

Not all of the impacts of dust are positive.  A recent paper has shown that the Eyjafjallajökull eruption reduced the productivity of Whimbrel during the next two years.  See Whimbrels & dust by Borgny Katrínardóttir et al.

Not all species are affected in the same way

Although the long-term effects of dust were clearly present for all birds, when considered together, and for the suite of common birds that were widely recorded during the Large Scale Survey, the clearest patterns appeared in the wader data, as shown below.  In dry areas (middle) and wet areas (right) there are far more waders in regions of the country that have experienced more dust deposition.  The number of individuals tripled between the lowest and highest classes of dust deposition.  Unsurprisingly, there were more waders in wetland areas, as they attract higher numbers of species such as Dunlin, Black-tailed Godwits and Redshank. In farmed areas (left), where slurry and artificial fertilisers are used, the local effects of dust deposition are masked.

The variation in mean (± SE) abundance of ) waders in agricultural habitats, dry habitats and wet habitats in areas of lowland Iceland with differing levels of dust deposition rate (7 = highest deposition rate). Reproduced from Gunnarsson et al 2015.

The variation in mean (± SE) abundance of  waders in agricultural habitats, dry habitats and wet habitats in areas of lowland Iceland with differing levels of dust deposition rate (7 = highest deposition rate). Reproduced from Gunnarsson et al 2015.

At the individual level, five of the seven common wader species all showed a significant response to variation in dust deposition rates (Black-tailed Godwit, Whimbrel, Golden Plover, Redshank & Otstercatcher).  The trends for Snipe and Dunlin were not significant.

What will happen in the future?

Iceland is a country with many active volcanoes and there is always the potential for another eruption that could produce a similar ash plume to that of Eyjafjallajökull in 2010, if basaltic lava erupts beneath a glacier.  Until this happens, smaller eruptions will produce new material in smaller quantities, whilst wind and water will redistribute the dust that has already been deposited. Given that most of the major dust sources are located at glacial margins and in floodplains, and that Icelandic glaciers are retreating due to climate warming, it is likely that volcanic dust inputs will increase in the future, which would have a negative effect on air quality in Iceland, but potentially a positive effect on lowland ecosystem productivity in general. This study shows that dust releases can have large-scale and long-lasting effects across food-webs.

This study was published as: Ecosystem recharge by volcanic dust drives broad-scale variation in bird abundance

Tómas Grétar Gunnarsson, Ólafur Arnalds, Graham Appleton, Verónica Méndez and Jennifer A. Gill  Ecology and Evolution 2015; 5(12): 23862396


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

Introducing WaderTales

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

The choice of topics will reflect personal interests, so there will be plenty about Black-tailed Godwits and the international team of scientists who study their behaviours and life-histories.  I hope that these blogs will be of particular interest to the hundreds of people who contribute their sightings of colour-ringed Black-tailed Godwits to the ever-expanding database of movements.

The first blog appeared on Monday 28 September, telling the story of why areas of Iceland that have been subject to higher deposits of volcanic dust can support up to three times as many waders as those that have received least.

Photo: Tómas Gunnarsson

Photo: Tómas Gunnarsson

On 2 October the second blog outlined new research which aims to explain why some Icelandic Oystercatchers migrate while others stay in Iceland – and how this might impact upon our understanding of how migration patterns change.  As this project unfolds, colour-ring sightings from birdwatchers are once more going to be very important.

By the end of October I hope that there will be a piece on the Black-tailed Godwits of Cley and another on the RSPB’s research into Lapwing predation.

Comments and suggestions will always be welcome.

Graham Appleton

GFA in Iceland