Grassland management for Stone-curlew

Detailed studies of a small number of Stone-curlews, breeding in Breckland in the east of England, give some clues as to how to provide the right habitat mix for these big-eyed, nocturnal waders. Increasing structural diversity, by ploughing and/or harrowing areas of grassland, can create an attractive network of nesting and foraging sites for breeding and non-breeding adults.

In a 2021 paper in Animal Conservation, Rob Hawkes and colleagues from the University of East Anglia, RSPB and Natural England give us insights into the daily lives of Stone-curlews nesting in the dry grasslands of East Anglia. By fitting five individuals with GPS tags and following their movements they were able to establish which habitats are used at different stages of the breeding season.

The Stone-curlew is the only migratory member of the thick-knee family. England is at the north-western limit of a breeding range that stretches east to the steppes of Kazakhstan, with birds wintering in southern Europe, North Africa, the Arabian Peninsula and the Indian sub-continent. Most English birds spend the winter months in Spain, Portugal, Morocco or Algeria but a small number are known to cross the Sahara. Stone-curlews return to East Anglia in March and April.

Unmodified grassland in the Brecks of East Anglia provides limited feeding opportunities for Stone-curlews
Creating heterogeneity within areas of grassland by ploughing and/or harrowing patches

During the twentieth century, numbers of Stone-curlew across Europe fell significantly, as mechanized farming expanded. The East Anglian population had dropped to fewer than 100 pairs by 1985 and it took huge conservation efforts to increase this to 200 pairs. Breeding birds are now typically to be found in sparsely-vegetated ground, often in spring-sown crops, on dry heathland or in semi-natural grassland areas, including those used for military training. Preferred food items, such as earthworms, soil-surface invertebrates, slugs and snails, are easier to find in areas of bare and broken ground than in thick grass, so grazing is an important part of conservation action on heaths and in grassland areas.

Each of these square treatments covers a hectare

The UK’s migratory Stone-curlew population has received a huge amount of conservation support, on the back of detailed studies of the species’ breeding ecology (Green et al. 2000).  Tremendous efforts have been made to maximise chick production in farmland, with conservation staff and volunteers working with farmers to monitor breeding pairs, so that they can protect nests and chicks during crop-management operations. In the long term, however, such interventions are too labour-intensive to be sustainable. Can equivalent benefits accrue if more Stone-curlews nest successfully in semi-natural grassland, where the costs of conservation subsidies are lower than in intensively farmed arable cropland?

The study that is reported in the 2021 paper in Animal Conservation took place in an extensive area of semi-natural grassland (nearly 40 km2) that is surrounded by a mosaic of arable farmland. The aim was to understand whether ploughing or harrowing patches of grassland can provide suitable foraging areas, and which other habitats are important.    

Tracking Stone-curlews

GPS tag attached to the back of a Stone Curlew

Stone-curlews are predominantly nocturnal feeders so some form of remote tracking device was needed to understand their movements. GPS loggers were fitted to five adult Stone-curlews during the breeding season. Individuals were caught at night using small, beetle-baited, elastic-powered clap-nets or in the daytime using nest-traps. Each individual was fitted with a 5.2 g solar-powered nanoFix Geo PathTrack GPS tag and an external whip antenna. GPS data were downloaded to a remote base station through a radio connection. Tagged birds were visited at least once a week to establish whether they were still nesting, if they had chicks or had finished breeding.

Where did they go?

One, two and three hectare plots of disturbed ground had already been created within Breckland’s grassland and heathland areas, prior to this study, as described in the paper and discussed in the blog Curlews and foxes in East Anglia. It was already clear that these plots were favoured as nesting sites but does disturbed ground also provide additional feeding opportunities for adult birds – including pairs nesting nearby on arable fields?

Using a telescope to point the base station ‘reader’ at a bird wearing a GPS logger

Three male and two female Stone-curlews were tracked for more than nine weeks (67 to 102 days), yielding 510 GPS fixes during nesting and 1371 post-breeding. There were some fixes in the pre-nesting phase and also during the chick-rearing phase but too few to be considered for analysis. Analytical methods are detailed in the paper.

During the nesting period, what was presumed to be the off-duty bird of each pair was found within 1 km of the nest on 90% of fixes. The mean distance from the nest during daytime feeding was about 100 m but, at night, tagged birds travelled five times as far, on average. They travelled furthest when heading for pig-fields and manure heaps.

  • Relative to closed, undisturbed grassland, nesting Stone-curlews were two- to three-times as likely to forage on disturbed-grassland during night and day, but especially during the day.
  • Night and day, ‘sugar beet or maize’ fields were used more than unmodified-grassland but similar to disturbed-grassland.
  • Nocturnally, Stone-curlews were ten-times as likely to use ‘pig fields or manure heaps’, when compared to undisturbed grassland.
  • The furthest distance travelled was just over 4 km, which is further than previously thought.
Stone-curlews will fly a long way to feed in pig fields

In the post-breeding period, tagged birds travelled up to 13 km to forage, with 90% of nocturnal foraging locations found to be within 5 km of day-time roosting sites.

  • Tagged birds were approximately 15-times as likely to use either disturbed-grassland or arable fallows when compared to undisturbed grassland.
  • Use of the category ‘pig fields or manure heaps’ was nearly as strong (factor c. 10), in comparison to undisturbed grassland.
  • Open crops in the categories ‘sugar beet or maize’ and ‘vegetable or root crops’ were also used more than undisturbed-grassland (factor c. 2).

Conservation messages

In England, there has been a long-term focus on trying to maximise Stone-curlew productivity within arable farmland, especially in East Anglia but also in Wessex. As suggested earlier, this is expensive – foregone production requires high subsidies and interventions by conservation staff are time-consuming. A French study, written up in Ibis by Gaget et al., seriously questions the viability of Stone-curlew populations within intensively managed arable farmland, even with conservation support. Given these problems, should conservation efforts focus on supporting and building up grassland populations?

In a previous tracking study, thirty years previously, Green at al. found that short semi-natural grassland provided suitable foraging habitat for Stone-curlews. Much has changed in Breckland in the intervening period, with the collapse of the rabbit population and an increase in the amount of outdoor pig-rearing. As the short swards of rabbit-grazed grassland have disappeared, Stone-curlews seem to have increasingly taken advantage of alternative opportunities offered in pig fields.

Previous attempts to replicate the grazing efforts of rabbits have involved increasing livestock numbers but this study shows that physical ground-disturbance interventions immediately and effectively create alternative foraging habitat. The authors suggest that multiple areas of disturbed-ground, close to the edge of large grassland blocks, can provide a network of nesting and foraging habitats, whilst allowing access to a mixture of feeding opportunities in the surrounding arable farmland. Of course, nobody is suggesting that intensive outdoor pig-rearing is a positive addition to the habitat mix, as it involves nutrient run-off, ammonia leakage into fragile plant-rich heathland, and pelleted feed attracts corvids (which are known to predate eggs).

The effect of creating ploughed or harrowed plots is almost immediate, in terms of prey availability. In more detailed studies of the effectiveness of slightly different ground-disturbance options, the research team found a strong selection preference only one year after the treatments were first implemented. In the longer term, these areas may become increasingly important, if young birds recruit to the local population and seek out these features. The researchers suggest that a bespoke, ground-disturbance agri-environment option might open up new breeding opportunities within semi-natural grasslands that are currently dominated by tall, closed swords. 

In England, conservation of dry grasslands and heathlands has tended to focus on the preservation on charismatic plant communities, an approach that may have been too gentle and conservative for other taxa. Whilst this study demonstrates that adding pockets of disturbed ground appears to benefit Stone-curlews, previous studies, conducted by this research team, showed benefits for Woodlark (Hawkes et al. 2019), Eurasian Curlew (Zielonka et al. 2019, summarised in Curlews and foxes in East Anglia), and rare, scarce or threatened dry-grassland invertebrates (Hawkes et al. 2019). Similar disturbance techniques have been shown to potentially benefit other grassland-breeding waders, such as Mountain Plovers (Augustine & Skagen 2014) and Upland Sandpipers (Sandercock et al. 2015) in North America, and Sociable Lapwings in Kazakhstan (Kamp et al. 2009).

Paper

This is a summary of a 2021 paper in Animal Conservation:

Effects of experimental land management on habitat use by Eurasian Stone-curlews. Robert W Hawkes, Jennifer Smart, Andy Brown, Rhys E Green, Helen Jones & Paul M Dolman.

Each summer, farmers, volunteers and conservation staff work together to monitor and protect nesting Stone-curlews on farmland, grasslands and heaths in eastern and southern England. Thanks to all of these people, the number of pairs of Stone-curlew in England is holding steady, at over 300 pairs. Progress was reviewed at a conference in 2017, as you can read in this layman’s report and this technical report. More guidance for landowners can be found here.


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.

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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.

Trees, predators and breeding waders

When trees are planted in open habitats that support breeding waders, numbers usually decline pretty quickly. Trees not only directly remove once-occupied habitat, they are also thought to attract predators, by providing somewhere to hide. In their paper in Restoration Ecology, Mark Hancock and colleagues investigate the distribution of thousands of scats of mammalian predators, in order to understand predator activity in landscapes associated with open bogs and forest edge. They were particularly interested in seeing how long it takes for predators to move out of an area when trees are removed and the land once more reverts to blanket bog.

This study took place alongside a project to repair damage to the vast Flow Country blanket bog (northern Scotland), that occurred in the 1980s, when non-native conifer trees were planted in areas of deep peat that had been drained and deep-ploughed. Such forestry practises would nowadays be prohibited.

More trees

The spread of trees can occur naturally, as the northern treeline moves further north or as trees grow higher in mountain regions, or it can be imposed or accelerated when trees are planted in previously open environments. Warmer temperatures create more opportunities for afforestation and politicians seem to be responding to rising CO2 levels by opting for what seems like an easy win – ‘let’s plant more trees’. In the right places, using appropriate native species, woodland can help to capture carbon**, support woodland wildlife and provide multiple other benefits to society. However, if afforestation focuses on open wet landscapes it can potentially threaten ground-nesting wader species such as Dunlin and Curlew.

** link to The value of habitats of conservation importance to climate change mitigation in the UK by Rob Field and colleagues in Biological Conservation.

As Mark Hancock and colleagues indicate in the abstract of their paper, afforestation of formerly open landscapes can potentially influence mammalian predator communities, with impacts on prey species like ground-nesting birds. In Scotland’s Flow Country, a globally important peatland containing many forestry plantations, earlier studies found reduced densities of breeding waders on open bogs where forestry plantations were present within 700 m. See Hancock et al. 2009 and Wilson et al. 2014. A previous WaderTales blog discussed whether apparent avoidance is due to actual or perceived predation risk (See Mastering Lapwing conservation) but whichever it is, adding new woodland to open wetland habitats has the potential to affect sensitive breeding waders.

Fox scat

There have been many studies looking at the effects of trees on breeding waders but the key differences in this case were that researchers monitored how mammal distributions changed as woodland was removed, in an effort to restore biodiversity and valuable blanket-bog habitats. Spoiler alert: it takes several years to reduce predator numbers!

By counting scats of species as diverse as fox and hedgehog the team were able to address three questions:

  • Did scat distributions vary between open bog, forestry plantations, and former plantations being restored as bog (‘restoration’ habitats)?
  • How fast did scat numbers change in restoration habitats?
  • Were scat numbers different in bogs with differing amounts of nearby forestry?

Counting the poo

Forestry transect

The analyses in this paper are based upon surveying 819 km of track verges, which yielded a total of 2806 scat groups (groups of scats that could have come from one animal) from a variety of predators. I smile when days and days of painstaking fieldwork are summarised in a sentence. “We measured summer scat density and size over 14 years, in 26 transects 0.6-4.5 km in length, collecting data during 93, 96 and 79 transect-years in bog, forestry and restoration habitats respectively”. There is no mention of midges either!

The Flow Country is host to a range of predatory mammals. Hedgehog, Wildcat, Red Fox, Badger, Pine Marten, Stoat and Weasel are native species, while introduced species like Feral Ferret and American Mink may be threatening the area. A 10 mm diameter scat could have been produced by one of six or more species – and increasingly it has been shown that genetic methods, which were outside the budget of this study, are needed to properly identify species from a scat. As all of these species prey on the eggs and/or chicks of breeding waders, the study treated them as a ‘guild’ of animals having similar potential effects.

In April each year, fieldworkers – many of them volunteers based at RSPB’s Forsinard Flows reserve – walked along each of the transects, removing all of the scats from the tracks and track-edges. In July, scats and scat groups that had been deposited on the tracks during the breeding season were counted, measured and their positions recorded using GPS (see paper for details).

Nine transects were in open bog habitat, that remained broadly unchanged throughout the study, 8 were in forestry plantations, 8 were in forestry plantations that were cleared and then restored during the study and 1 site was already a restored plot. For ‘restoration’ transects, the number of years since felling was used as a measure of the length of time under restoration management. In these restoration areas, the brash that was left after felling gradually rotted away or became buried by recovering bog vegetation as re-wetting management (e.g. drain blocking) took effect.

Where’s the poo?

Transect through bog

Predator activity in different habitats and over time. For bog and restoration habitats, scat group density was relatively low throughout the study, averaging around 1 to 2 scat groups per km. In forestry transects, scat group densities started at similar values, but rose approximately eight-fold over the study period, as the forests matured. In the final year of the study, scat group densities in forestry averaged around eight groups per km – approximately twice the figures in restoration and six times the figure in bog habitats. There is a suggestion that more mature forests may have suited Pine Martens, in particular: this species was recorded in the heart of the Flow Country for the first time during the study period.

Trees removed – restoration transect

Predator activity once trees are removed.  Scat group density differed significantly between restoration areas of different age classes. In recently-felled sites (1-5 years), densities were about 2.4 groups per km, rising to 4.0 in the middle period (6-10) and falling to 1.3 later (11-14 years). The authors suggest that tree removal may lead to a flush of nutrients, grasses and then small mammals, thereby explaining the increase in scat densities during the middle stage (6-10 years). The paper demonstrates that it takes several years for mammal densities to fall back to ‘natural’ levels, after tree removal.

Pine Martens have moved into the area

Predator activity close to forests. Scat density on open bog transects was significantly affected by the presence of at least 10% forestry cover within 700 m. There was an estimated 2.9 times (95% confidence limits 1.4 to 6.0) higher scat density at bog transects which contained over 10% cover of forestry within 700 m, compared to bog transects with less forestry nearby. Scottish studies of breeding waders have shown that species such as Golden Plover, Dunlin and Curlew avoid areas close to forestry and the paper includes references to several other similar studies elsewhere.

The Conservation picture

As pointed out by Hancock et al in their Discussion, scat densities in forestry reached much higher values than those of open bogs, especially as the plantations matured, implying that afforestation had strongly altered patterns of mammalian predator occurrence in this formerly open landscape. It took ten years of restoration management to drive down scat densities to levels similar to those of open bogs but, as the authors note, peatland restoration is a rapidly developing field and newer techniques may allow faster restoration, with both biodiversity and soil carbon benefits.

These findings have implications way beyond the scope of this study, three examples of which are included below:

Commercial forestry is seen by some as a way of capturing carbon and can provide opportunities to restore our woodlands, especially our native woodlands and their associated biodiversity. However, given the vulnerability of ground-nesting birds to predation, and the potential for afforestation to markedly affect predator communities, care needs to be exercised when considering afforestation of open landscapes.

Warmer climates offer opportunities to add forestry to the mix of land use options in areas in which the growing season used to be considered too short. For instance, there is significant development pressure in Iceland to plant large areas of non-native commercial forestry. Given that the country holds half or more of Europe’s breeding Whimbrel, Dunlin and Golden Plover this is a contentious issue. This AEWA report is important: Possible impact of Icelandic forestry policy on migratory waterbirds.

In Ireland, it has been suggested that a patchy distribution of relatively new forestry plantations may be one of the factors contributing to the drastic decline of Curlew numbers. (Ireland’s Curlew crisis describes a 96% decline in just 30 years). It has been proposed that some of these patches should be removed. The Hancock et al paper shows how long it might take to make a difference – ten years may simply be too long for Ireland’s breeding Curlew.

Read more

The paper that forms the basis of this blog is:

Guild-level responses by mammalian predators to afforestation and subsequent restoration in a formerly treeless peatland landscape by Mark H. Hancock, Daniela Klein and Neil R. Cowie. Published in Restoration Ecology. https://onlinelibrary.wiley.com/doi/abs/10.1111/rec.13167


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

Scotland’s Dotterel: still hanging on

blogpic brooding

Dotterel brooding chicks

Within the UK, the Dotterel now only breeds on plateaux in the highest Scottish mountains, restricted by habitat that is more commonly found in the arctic or arctic-alpine regions. 

As soon as climate change became apparent, the Dotterel turned into a focal species for ornithologists who were interested in how species would be affected by climate heating. Their fate seemed to be sealed; put simply, there is nowhere colder in Britain to which to retreat when faced with changing habitats and/or breeding conditions.

A 2020 paper by Steven Ewing, Alistair Baxter and colleagues explores the potential ways that changing environmental conditions may be driving the Dotterel’s decline.

Life history

Scottish Dotterels don’t actually spend much time in Scotland, with most birds arriving in early May and leaving within three months. The large part of the year is spent in North Africa, and the plains to the northwest of the Atlas Mountains in Morocco seem to be a particularly important wintering grounds for Scottish birds. Migration north and south appears to be direct, with few European reports of ringed birds in spring and autumn. There is some evidence that Dotterel move further south within North Africa as winter progresses (Whitfield et al 1996), perhaps responding to rainfall patterns.

blogpic map

In May, the numbers of males and females on Scottish breeding sites are roughly equal but many females leave their males sitting on a first clutch of eggs and then depart, leading to an observed drop in sex ratios to about 10:1. Females ringed in Scotland have been spotted breeding with Norwegian males later in the same season and this onward movement to areas with later snow-melt may well be a normal pattern. Indeed, many Dotterels seen on passage in May, often on traditionally used fields or mountain tops south of the Scottish Highlands, may loop north, passing through Highland nesting haunts and then heading northeast into Scandinavia.

A species in decline

blogpic Alistair

Alistair Baxter points to a Dotterel nest that’s right next to a path following the line of a ridge

Dotterels in Britain are at the south-western limit of the species’ global range. They breed almost exclusively in arctic-alpine habitats above 750 m, particularly on Racomitrium moss-heaths that are so characteristic of the flatter topped mountains. These habitats are of high conservation concern, with a tapestry of nationally-rare alpine and arctic plant species.

Scottish Dotterel have been well-studied for over eighty years, a process that was started by Desmond Nethersole-Thompson in the 1940s (detailed in his classic monograph The Dotterel, 1973) and has involved the authors of the Global Change Biology paper since 1987. Some of the areas featured in this paper were studied by Nethersole-Thompson.

An earlier WaderTales blog (Dotterel numbers have fallen by 57%) suggested a number of possible reasons for declines – habitat changes, increased predation and increased disturbance in the Scottish Highlands, compounded by issues affecting the wintering population in North Africa. In the 2020 paper, Ewing et al look in more detail at the potential roles of these changes

Climate and habitat change in Scotland’s mountains

Mountains in Britain are subject to a range of environmental drivers of change that may potentially influence Dotterels, but the logistical challenges presented by working in these environments means that there is rarely good data documenting these changes. This study focuses on snow cover and nitrogen deposition.

blogpic change

The amount of snow-cover is important for cold-adapted species of plants and animals; it insulates the ground in winter and slows up warming in spring, thereby creating a relatively stable environment.  Potential consequences of changes in winter snow-lie for alpine birds might include:

  • A longer growing season for plants, with taller vegetation that reduces the suitability of these areas for species that favour shorter swards.
  • Fewer snow patches, around which Dotterel feed, perhaps also leading to a reduction in peak insect abundance that may not match feeding requirements of chicks.

blogpic nestLots of research carried out in the UK shows that nitrogen deposition is an important driver of upland vegetation change.  Higher deposition of nitrogen tends to result in a reduction of alpine specialist plants, including species of mosses that form key breeding habitats for Dotterel.

The earlier WaderTales blog (Dotterel numbers have fallen by 57%) suggested other possible reasons for Dotterel declines on the breeding grounds, including increased predation and increased disturbance in the Scottish Highlands. While these potential drivers of change could not be tested, due to a lack of data, they are considered in the paper’s Discussion.

Study system

The data that lie at the heart of the Global Change Biology paper have been collected over three decades. Two different but complementary data sources were used in the study.  Firstly, Dotterel were counted at between 128 and 198 alpine sites in the UK during three national surveys in 1987-88, 1999 and 2011.  These censuses focused upon suitable breeding habitats, especially Racomitrium heath, with the latter two surveys successfully covering more than 50% of identified breeding areas.  Secondly, between 1987 and 1999, a smaller cohort of alpine sites were surveyed with far greater frequency (between 40-60 times) as part of SNH’s Montane Ecology Project, where the aim was to study the Dotterel’s breeding ecology in far more detail. The 2020 paper contains detailed information about site use and the parameters that were measured/assessed (elevation, slope, area, snow cover, nitrogen deposition, summer temperature etc.)

blogpic surveyEach site visit involved a lot of climbing, so many of the sites were visited only once per season, with more frequent visits to just 15% of the sites. Having accompanied Phil Whitfield (one of the authors) up one mountain, on one day, I have huge respect for the effort that each data-point represents.  Once up on the tops, observers covered the study areas thoroughly, passing within 100 m of every point and scanning frequently. This has been shown to provide a good count of breeding males.

The authors used their data to investigate whether key potential drivers of environmental change in Scottish mountains (snow-lie, elevated summer temperatures and nitrogen deposition) may have contributed to the population decline of Dotterel.  They also consider the role of rainfall on the species’ wintering grounds in North Africa. The key questions they address are:

  1. Is there evidence of an uphill shift in the elevation of the Dotterel’s breeding range during the study period (1987-2014)?
  2. Are changes in the density or site occupancy of breeding male Dotterels associated with the size, connectedness or topographical aspect of alpine sites?
  3. Does spatial variation in atmospheric nitrogen deposition account for variation in density or occupancy of breeding males at alpine sites?
  4. Are patterns of snow cover or late summer temperatures associated with density or occupancy of male Dotterels at alpine breeding sites?
  5. Do densities of breeding male Dotterels on alpine sites vary with conditions on the North African wintering grounds, as reflected by winter rainfall?

blogpic gloaming

What has changed?

The results are presented in two ways. Data from the period of intensive studies, between 1987 and 1999, are used to try to understand factors influencing annual changes in the number of nesting males. Examination of changes between 1987-90 and 2011-14 gave some indication of factors affecting longer-term trends – something that is important to understand when Dotterel can live for at least ten years.

Densities of breeding male Dotterel in mountainous regions of Scotland declined between 1987 and 1999 and, over the longer-term, site occupancy fell from 80% in 1987 to only 36% in 2014. Densities of breeding males declined disproportionately from lower-lying sites, which resulted in the Dotterel’s breeding range retreating uphill at a rate of 25 m per decade.

Geographically isolated sites appear more likely to lose breeding Dotterel. This makes sense; playback studies in Russia have shown that passing flocks of Dotterel respond to calls, suggesting that birds will be attracted to already-occupied locations.

Settlement patterns were linked to snow-cover.  Generally, Dotterels appear to prefer to settle on higher sites, but late-lying snow at higher elevations appears to deprive them of suitable breeding habitat.  Rather than delay nesting, it seems that these birds then choose to move to lower snow-free sites to breed. Long-term changes in snow cover are poorly documented in high-elevation habitats in Scotland, so it is difficult to know whether the substantial declines observed for Dotterel in recent decades reflect systematic changes in snow-lie.

blogpic snow patch

Nitrogen deposition was shown to be negatively associated with densities of males nesting at lower and intermediate elevations.  The primary impact of nitrogen deposition on Dotterel is likely to be via effects on the species’ favoured Racomitrium moss-heaths, with greater nitrogen levels increasing the rate of moss decomposition and favouring accelerated grass growth.  This presumably results in these habitats becoming increasingly unsuitable for breeding Dotterel.

blogpic chick

Will this chick makes it to Morocco? If it does, how will the conditions it experiences in the non-breeding season affect its probability of return to Scotland?

High rainfall in North Africa seems to lead to higher densities of breeding male Dotterel two springs later, suggesting that wintering ground conditions can potentially influence population dynamics of this alpine-breeding bird.  Similar positive impacts of North African rainfall have also been seen in Ring Ouzels that breed in the UK (Beale et al. 2006).

Dotterel inhabit open farmland and sub-desert steppes in North Africa, where seasonal rainfall brings a flush of vegetation growth and insect abundance. Higher winter rainfall may increase prey availability and Dotterel survival rates but that would be reflected in the arrival numbers in the next spring. The lag of an extra year suggests that low rainfall levels may mostly affect young birds, perhaps delaying recruitment of some Dotterels until their second breeding season.

Conclusions

blogpic juvvyPopulation declines and site abandonment by Dotterel in Scotland during the last three decades have largely occurred at lower elevations, fitting with the traditional idea of climate change limiting the available climate space for alpine breeding species. However, this study found relatively limited evidence that the decline in the breeding population is being driven by climatic factors on the breeding grounds.

Snow cover does seem to influence year-to-year variation in the species’ elevational distribution in Scotland, potentially because a smaller population may now be increasingly settling on higher sites that perhaps were previously unavailable, due to extensive snow cover.  There was also some evidence that greater nitrogen deposition reduced breeding densities of Dotterel at low to intermediate elevations, perhaps by decreasing the suitability of Racomitrium moss heath breeding habitats.  It is also possible that there may have been a redistribution of birds, with newer generations moving further north, to more suitable sites in Norway. (There is a WaderTales blog about this sort of Generational Change mechanism in waders, focusing on Black-tailed Godwit).

Given that Dotterels spend so little time in Scotland, a big gap in our understanding is what is happening in Morocco, where adult Scottish Dotterel spend three-quarters of the year and where young birds may also spend their first summer. How are factors such as rainfall and land-use (particularly farming methods) affecting Dotterels? Might changes in these areas affect other species of migrant that leave northern Europe at the end of the breeding season? Perhaps conservation scientists need to head south for the winter to find out?

Read more in the paper

Clinging on to alpine life: investigating factors driving the uphill range contraction and population decline of a mountain breeding bird. Steven R. Ewing, Alistair Baxter, Jeremy D. Wilson, Daniel B. Hayhow, James Gordon, Des B. A. Thompson, D. Philip Whitfield & René Van der Wal. Global Change Biology.

blogpic dewy


GFA in IcelandWaderTales blogs are written by Graham Appleton, 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.

@GrahamFAppleton

 

Where to nest?

pic whimbrelThere is nothing more obvious than an Oystercatcher sitting on his or her nest, but a brooding Snipe can be invisible until almost trodden upon. Which strategy works better: nesting in plain view but laying cryptically camouflaged eggs or hiding yourself and your nest in a clump of grass? Which species is most likely to hatch a successful brood of chicks and in what circumstances? In a 2020 paper in IBIS, Becky Laidlaw and colleagues analysed nest site characteristics and nest locations of 469 wader nests in Iceland in order to provide some answers

The perils of ground-nesting

pic hatching whimbrel

Hatching Whimbrel eggs, with the tell-tale shell fragments that signal a nesting attempt has been successful

Almost all waders are ground-nesters, which makes them highly vulnerable to a wide range of nest predators. To reduce the risks of predation, different strategies have evolved. In some species, nests are placed out in the open, and the camouflage is provided only by mottled egg colouration that resembles the background. In other species, nests are secreted in vegetation, meaning eggs and incubating adults are concealed from predators.

In both groups of species, the risk of nests being predated might vary, depending on the surrounding habitat. For open-nesting species, for example, clutches that are laid in large patches of similar habitat may be harder for predators to locate. The same could apply to closed-nest species that hide their nests; Snipe nests may be tricky to find in extensive areas of long grass but perhaps more at risk if there are only a few suitable clumps of long grass that predators need to check out.

pic hidden Redshank

Iceland: a wader factory

tableAs discussed in previous WaderTales blogs, particularly Do Iceland’s farmers care about wader conservation? Iceland is hugely important as a European ‘wader factory’. As farmland elsewhere has become less suitable for species such as Redshank and Snipe, the global importance of the country has increased (see table alongside for most recent figures from an AEWA report)  With this in mind, it is important to understand the factors that underpin the population dynamics of Iceland’s breeding waders.

Working in South Iceland, Becky Laidlaw and her co-authors tried to find as many nests as possible during the summers of 2015 and 2016. This area is largely a mosaic of open habitats, although there are more patches of forestry than there were twenty years ago. Most of the Southern Lowlands area is farmed, on a gradient between intensive and semi-natural, and this is reflected in the distribution of breeding waders (see Farming for waders in Iceland).

pic rope

Dragging a light rope across the vegetation to flush nesting birds

For this project, nests were located by surveys from vehicles and on foot, through observation of incubating adults, systematic searching, incidental flushing of incubating adults and rope-dragging (dragging a 25 m rope, held between two fieldworkers, lightly across vegetation) to flush incubating adults.

The analysis in the resulting paper in IBIS focuses on 469 nests of three open-nesting species (Oystercatcher, Golden Plover and Whimbrel) and three species that hide their nests in tall vegetation (Redshank, Snipe and Black-tailed Godwit). The team recorded the habitat and vegetation structure around each nest (at the nest, within a 5 m x 5 m square and in a wider 50 m x 50 m square) and worked out which nests hatched successfully and which were predated. The date and time of predation were determined, where possible, with nest-cameras providing extra information for some nests. Cameras captured nest-predation events involving Arctic foxes, Arctic Skuas, Ravens and sheep.

Interestingly, 2015 and 2016 were very different wader breeding seasons. The graphic below shows the mean temperatures for the months from April through to July (encompassing the wader breeding season at this latitude) were much cooler in 2015 than in 2016, representing average monthly difference of between 1.5°C and 2.5°C. At high latitudes these figures translate into very different rates of vegetation growth.

pic pretty graph

First, find your nest

When nests were first located, their positions were marked and referenced using GPS. Eggs were floated in water to provide an estimate of laying date and thereby predict hatching date. As the chick develops within an egg, the density of the egg falls. A newly laid egg will lie on the bottom of the flotation vessel. Over the next few days the ‘blunt end’ rises until the egg is still touching the bottom but vertical. Eggs in the late-development stage float ‘point-end-down’, with the latest eggs floating at an angle to the vertical (method described by Liebezeit et al.).

pic skua-ed goldie eggs

This Golden Plover nest was probably predated by an Arctic Skua

Nests were considered successful if one or more eggs hatched, and predated nests were defined as those that were empty in advance of the predicted hatch date or those without any eggshell fragments in the nest (a sign of successful hatching). To determine the time and date of nest failures, iButton dataloggers were placed in a randomly selected subsample of nests. These loggers recorded a temperature trace every ten minutes. A sharp and permanent decline in nest temperature below incubation temperature indicates nest predation. In both study years, motion-triggered cameras were deployed on a sample of open-nesting species to determine the predator species active on these nests.

When each nest was first located, the percentage of eggs visible from directly above the nest was estimated and the habitat surrounding each nest was assessed in the field at three spatial scales: the nest cup, the 5 m x 5 m and the 50 m x 50 m area surrounding each nest. Details are in the paper.

Which nests survive through to hatching?

Over the breeding seasons of 2015 and 2016, the outcomes of 469 wader nests were assessed. 259 hatched successfully (55%), 192 were predated (41%), 13 were abandoned, 7 were trampled and 2 were mown. A nest-loss rate of 40% is fairly typical for ground-nesting waders, when compared to studies in different countries and habitats.

pic fox attack

Daily nest predation rates did not vary significantly in relation to the habitat heterogeneity or the extent to which the dominant habitat covered the area surrounding the nest, at either 5 m x 5 m or 50 m x 50 m scales. Most clutches were laid in habitats that were the same or similar to the surrounding areas. Where there were differences, the dissimilarity between the habitat at the nest cup and in the surrounding area did not influence daily nest predation rates for open- or closed-nest species. Although nest predation is high, at about 40%, incidence of predation events appears to be unpredictable – or even random.

pic snipe nest

In cold spring conditions, Icelandic Snipe are not able to hide their nests

Daily nest predation rates were significantly higher for closed nests (Redshank, Snipe and Black-tailed Godwit nests) in which a greater percentage of the clutch was visible. This suggests that the onset and rate of vegetation growth could potentially constrain the availability of suitable nesting locations for these species, and hence influence nest success, particularly among early season nests. This has been studied in Icelandic Black-tailed Godwits by José Alves and colleagues and is described in From local warming to range expansion.

For closed-nest species, the visibility of nests was significantly greater during the early part of the 2015 breeding season, when compared to 2016, due to slower grass growth in cooler conditions.  The higher predation rate of more visible nests of closed-nesting species was apparent even though nests were predated up to three weeks after egg visibility was measured. These findings suggest that early nesting attempts by concealed-nest species are unlikely to be successful in years when vegetation growth is delayed or slow. There can be major benefits of hatching early, with recruitment into breeding populations typically being lower for later-hatched chicks, so vegetation growth rates are likely to be really important to species that conceal their nests (Redshank, Snipe & Black-tailed Godwit in this study). However, given the ongoing trend for warmer springs at subarctic latitudes, the conditions in which early nests can only be poorly concealed are likely to be reducing in frequency.

In summary

pic goldie nest in habitat

Golden Plover nest set within a homogeneous habitat matrix

Perhaps surprisingly, nest predation rates were similar for open-nest and concealed-nest species and did not vary with vegetation structure in the surrounding landscape. However, nest-concealing species were about 10% more likely to have nests predated when the nests were poorly concealed, and the frequency of poorly concealed nests was higher at the start of the breeding season in colder conditions.

The paper at the heart of this blog is:

Vegetation structure influences predation rates of early nests in subarctic breeding waders. Rebecca A. Laidlaw, Tómas G. Gunnarsson, Verónica Méndez, Camilo Carneiro, Böðvar Þórisson, Adam Wentworth, Jennifer A. Gill and José A. Alves. IBIS. doi:10.1111/ibi.12827

pic sheep


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

 

 

Curlews and foxes in East Anglia

blog chicksWith Curlew populations in free-fall across much of the British Isles, researchers are trying to understand the reasons for poor breeding performance. At the same time, several groups are trialling emergency interventions, such as predator control and predator exclusion, to try to boost the number of fledged chicks. Sharing knowledge is crucial, so it’s great that a 2020 paper by Natalia Zielonka and colleagues in Bird Study adds to our understanding of nest-site selection and the reasons for nesting failures.

Breckland Curlew

When we think of Britain’s breeding Curlew, the traditional image that comes to mind is moorland, where displaying birds deliver their haunting, bubbling call across upland heather moor and sheep pasture. In lowland East Anglia, in the east of England, things are very different. Some Curlew nest on Breckland heaths, which are structurally similar to moorland, but you can also find nests in sugar-beet field, in military training areas and around airfields.

The Eurasian Curlew is now categorised as Near Threatened by IUCN & BirdLife International, due to populations declines (see Is the Curlew really near-threatened?). Figures from the Breeding Bird Survey for the period 1995-2017 show that the situation in England (30% decline) is less bad than Scotland (down 61%) or Wales (down 68%). The species is now too thinly spread to be monitored in Northern Ireland but we know that the breeding population in the Republic of Ireland dropped from 3,300 pairs to just 138 pairs in 30 years (more in Ireland’s Curlew Crisis). In this context, the hot-spot in Breckland (see left-hand map from Bird Atlas 2007-11) is significant, as is the fact that there are four 10-km squares in East Anglia where an increase in density was noted between 1988-91 and 2008-11 (right).

blog maps

Problems for Curlew

The main driver of UK Curlew decline is low breeding productivity, attributable to predation and reduced quality of breeding habitats (see review by Franks et al., summarised in Curlews can’t wait for a treatment plan). Research has informed habitat provision and demonstrated that legal predator control (of foxes, crows, stoats and weasels) can increase Curlew breeding success and abundance – but not in all cases.

blog flyingMuch of the research underpinning the above review was conducted in upland areas. What is happening in the flatlands of East Anglia and might any differences explain the apparent resilience – or even growth – of this population? Most lowland Curlew breed on dry grasslands and heathland, where physical ground-disturbance is increasingly advocated as a land management technique for other rare, scarce and threatened species, such as Stone-Curlew and Woodlark. How do these interventions affect breeding Curlew in the same areas?

Study site

Natalia and her colleagues studied Curlew in two extensive grass-heath sites that differed in predator density and management. Across both sites, vegetation structure had been modified, using ground-disturbance plots, as part of a wider multi-taxa experiment, aimed at increasing biodiversity and supporting key species such as Woodlark (paper in Ibis) and Stone Curlew (paper in Biol. Conserv.).  This disturbance involved creating  2 to 4 hectare plots of deep- or shallow-cultivated ground within the wider grassland/heathland environment.

Before the experiment began, and based on previous research elsewhere, it was assumed that Curlew would avoid physically-disturbed areas, given that Curlew have been shown to prefer to nest in rougher habitats with longer grass swards.  Wherever the Curlews decided to nest, it was predicted that nest survival would be higher on the site with lower predator density, that most clutches would be taken at night and that success would decrease through the season.

blog STANTA

The study was carried out in 2017 and 2018 across the Stanford Military Training Area (STANTA) and Brettenham Heath. Both sites contain extensive areas of dry grassland and grass-heath, surrounded by arable farmland and woodland. Generalist predator control on STANTA was largely carried out around Pheasant release pens, with little or none in most of the surrounding, open arable farmland and woodland. In contrast, Brettenham Heath was subject to continuous predator control across the whole site and in surrounding arable farmland (but not woodland). Brettenham Heath is also enclosed by a two-metre high deer fence with a single electric strand set 50 cm above the ground. There is more about the two sites in the paper (link below).

blog Brettenham

Across both sites, 64 experimental ground-disturbance plots were established in early 2015 and subsequently disturbed annually, using a variety of management techniques. Areas on STANTA that might have contained unexploded ordinance could not be disturbed – and were trickier to survey! In both years, nests were located between mid-April and late June, by visiting any area where Curlew had been seen and looking for adults sitting on, or walking back to, a nest.

Evidence of nest success

blog chickTo determine the date and timing of nest failure, temperature sensors were placed under the eggs. Nests were remotely checked every three-to-seven days, to confirm adults were still incubating, and the scrape was visited once a week to record any predation events (e.g. partial clutch predation). From three days before the predicted hatch date, nests were remotely monitored daily to accurately determine their fate. After hatching, the nest site was visited every three-to-five days, to observe adults and chicks from a vehicle, continuing until the chicks fledged or the breeding attempt had failed.

Three types of evidence can help to reveal the outcome of a nesting attempt:

  • Small chicks or alarming adults are seen in the vicinity of an empty nest.
  • Small shell fragments are found in the nest cup, indicating that chicks have hatched.
  • The temperature sensor reveals that adults kept the eggs warm for the whole incubation period.

A sudden drop in nest temperature can reveal the timing of predation and hint at the culprit. Other studies have shown that nocturnal visits are usually by foxes or badgers, or occasionally hedgehogs. In 2018, infra-red cameras, triggered by movement, were used on ten nests.

blog camera

Where to nest?

Unexpectedly, given that breeding Curlew in the uplands are usually associated with areas with longer grass, Breckland pairs were five- to six-times more likely to select disturbed plots than undisturbed grassland. Nearly half of nests were located on disturbed grassland across both years, which only occupied about 8% of the grassland area. Curlew are long-lived and site-faithful, so disturbed plots may have been created within already-established breeding territories. Whilst physical-disturbance interventions are unlikely to bring birds in from the wider landscape, this study shows that nest placement was more likely to occur on disturbed grassland within a pair’s home range. This suggests that local-scale management can influence nest placement within established breeding sites.

Disturbed grassland is characteristically bare and short compared to uncultivated grassland. Curlew may have placed nests in this habitat because it allows greater vigilance and/or because there is a greater abundance of some important prey for chicks than the surrounding grassland (information in paper by Hawkes et al.). Most nests were on shallow-cultivated plots (created with a rotary rotovator), with few on the barer deep-cultivated plots (created with an agricultural plough). There was taller vegetation and more ground cover in the shallow-cultivated plots.

blog tractors

Nest survival rates                                                                                                                       

Over the course of the two summers, 44 Curlew nests were monitored, of which 32 failed. 29 nests were predated, one was trampled by livestock, one was mown and one pair deserted (and then renested). Mean overall nest survival probability from start of incubation to hatching was 0.70 ± 0.18 SE at Brettenham Heath (where there was intensive predator control and fencing) and 0.16 ± 0.06 at STANTA (where predator control was patchy and the site was open). Overall breeding productivity was 0.16 ± 0.01 SE fledged chicks per nesting attempt. As predicted, daily nest survival rate decreased through the course of the nesting season.

The figure for STANTA represents low nesting survival, especially when compared to other lowland sites in England, and re-nesting following failure appeared infrequent. Productivity here is likely to be substantially below that required to maintain a stable population. Importantly, nest survival across the two sites was not influenced by ground-disturbance, which suggests that this management intervention did not increase nest exposure to predators.

Identifying the predators

D4_sheep_predation_20May

Sheep versus Curlew

Of the ten 2018 nests with nest cameras:

  • Three nests survived through to hatching.
  • Four were predated by fox (one during the day and three at night).
  • One nest was predated by an unknown predator (following camera malfunction).
  • One nest was predated by a sheep (two out of four eggs remained but incubation was not resumed and the other eggs were later taken by a crow).
  • A single-egg, late-season re-nesting attempt was abandoned three days after camera deployment (egg was later taken by a crow)

There was no effect of nest cameras on daily nest survival rate.

G1_Fox_predation_20May

Fox versus Curlew

Parent Curlews removed some of the temperature loggers but there were sufficient data to identify the timing of predation events for 23 nests. Of these, 17 events were during the night (13 nocturnal, four crepuscular) and six during the day. This nocturnal timing of nest predation was consistent with mammalian rather than avian predation, with camera traps and other evidence suggesting that foxes were the main perpetrators.

As expected, from the levels of predator control, nest survival was lower at STANTA than Brettenham Heath. The latter site was both fenced and subject to lethal fox control, delivering a breeding productivity well above that considered necessary for a sustainable population of Curlew. It is possible that a few fenced sites and others with high levels of predator control might be disproportionately responsible for the fact that Curlew appear to be doing better in the Brecks than in other areas.

Conservation implications

blog bare nestThe key finding of this project is that physical ground-disturbance, which is advocated as a conservation measure within lowland dry grassland and grass-heath for many rare, scarce and threatened species, also provides suitable Curlew nesting habitat, with no reduction in nest survival. Implementing ground-disturbance, particularly through shallow-cultivating, in areas with few or no mammalian nest predators, could provide a useful management tool for attracting breeding Curlew to safer areas.

An intervention to help Stone Curlew and Woodlarks was never designed to assist Curlew. Indeed, there was a prediction that Curlew would actively avoid areas that had been rotovated, in order to create bare patches in which the target species could nest and feed. In a rare case of serendipity, experimental research by Rob Hawkes, Paul Dolman and others has delivered a way of encouraging Curlew to nest in relatively small plots (2-4 hectares) around which it may be possible to run an electric fence. One of the big questions “How can we protect Curlew nests when they have such big territories?” might have become easier to answer. If ‘Curlew plots’ can be created within known territories, or even areas that seem good for Curlew, then they can potentially become the focus for protection.

Having spotted that Curlew seemed to be attracted to disturbed areas it is great that Natalia Zielonka was able to study this population, in order better to understand constraints that seem to be restricting productivity. Her research was undertaken as part of her MSc in Applied Ecology and Conservation at the University of East Anglia,

Further reading

blog RARThe paper at the heart of this blog is:

Placement, survival and predator identity of Eurasian Curlew Numenius arquata nests on lowland grass-heath. Natalia B. Zielonka, Robert W. Hawkes, Helen Jones, Robert J. Burnside & Paul M. Dolman.

Bird Study. DOI 10.1080/00063657.2020.1725421


GFA in IcelandGraham (@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.

 

Fennoscandian wader factory

 

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Nesting Temminck’s Stint – the smallest of the 22 wader species for which trends are reported

At the end of the summer, vast numbers of waders leave Norway, Sweden and Finland, heading southwest, south and south-east for the winter. In a 2019 paper by Lindström et al, we learn what is happening to these populations of Fennoscandian breeding species, as diverse as Temminck’s Stint and Curlew. The news for the period 2006 through to 2018 is basically pretty good – most populations have been stable and there are even some that have increased – but there are worrying signs for Broad-billed Sandpiper, Red-necked Phalarope and Whimbrel.

Breeding waders of Fennoscandia

blog mapAs a volunteer taking part in the Breeding Bird Survey (BTO/JNCC/RSPB) in the UK, I feel that I do my bit to monitor what is happening to local bird population – providing counts that build into national trends. The work involved in delivering indices for breeding waders across the area of Fennoscandia shown in the map is in a different league. Here, counters visit habitats as diverse as forests, wetlands, mires and tundra, within the boreal and arctic areas of Norway, Sweden and Finland. Some survey sites are so remote that access requires the use of helicopters.

Fennoscandia provides important breeding areas for a large set of wader species, and models suggest that these habitats may be particularly vulnerable to climate change, especially increasing summer temperatures. The 2006-18 analysis in Wader Study, the journal of the International Wader Study Group, presents population trends for 22 wader species. The trends are based on 1,505 unique routes (6–8 km long), distributed over an area that’s about four times that of the United Kingdom. 

blog surveyor

The surveys took place across the whole of Norway and Finland, and in the northern two thirds of Sweden, between 58°N and 71°N, which largely coincides with the boreal, montane and arctic regions of Fennoscandia. The systematic distribution of these routes ensures that the main habitats in these countries are sampled in proportion to the area they cover. The paper describes the methodologies used in the three countries and the way that data were combined, especially factors used to translate sightings of individuals into ‘pair-equivalents’.

Overview of results

blog mountainLooking at the results from across Norway, Sweden & Finland:

  • In terms of pure numbers, Golden Plover was the most commonly encountered wader species, followed by Wood Sandpiper, Snipe, Greenshank and Green Sandpiper.
  • The five most widespread species, seen on the highest number of routes, were Snipe, Green Sandpiper, Greenshank, Wood Sandpiper and Common Sandpiper.
  • Wader species richness and the total number of wader pairs were both higher with increasing latitude; the median number of wader pairs per 10 km increased from just below 3 at latitudes 58–60°N, to just above 26 at latitudes 69–71°N.
  • Using a multi-species indicator, the research team found no general change in wader numbers over the period 2006-18.
  • The trends were significantly negative for three species: Red-necked Phalarope (-7.9% per year), Broad-billed Sandpiper (-5.4% per year) and Whimbrel (-1.3% per year).
  • The trends were significantly positive for three species: Oystercatcher (+4.9% per year), Dunlin (+4.2% per year) and Wood Sandpiper (+0.8% per year).
  • There was no significant trend for another 16 species for which encounters were deemed to be frequent enough for analysis.
  • Population trends of long-distance migrants tended to be more negative than those of medium-distance migrants. This is discussed in detail in the paper.

blog wood sp habitat

Focusing on some key species

The Lindström et al paper is a tremendously rich source of information and references. Here are some species-specific highlights.

Oystercatcher. In the context of a species that is declining across NW Europe, the fact that there is a significant increase in Oystercatchers across Fennoscandia may be surprising. However, the authors note that there was a jump in numbers between 2006 and 2007 with little change since then.

blog l graphLapwing. The trends within the three Fennoscandian countries are very different. In Norway, there has been a dramatic decline (-15.2% per year during 2006–2018) and the Lapwing is now nearly extinct in many areas. The trend in Sweden is also significantly negative (-5.8% per year). In Finland, however, where the species is more widespread and numerous, there has been a strong increase (+5.9% per year) during the same period. See figure alongside.

Golden Plover. No significant change overall. There are some country-specific differences in trends, with a moderate decline in Norway being countered by a moderate increase in Sweden. 

Snipe. The overall trend of this species for each country indicates an initial decline followed by an increase. A similar pattern has been noted in the UK’s Breeding Bird Survey over the same period. 

blog whimbrel

Nesting Whimbrel

Woodcock. The trend for 2006–2018 is basically stable and similar in all three countries.

Curlew. There is no significant trend, overall, but populations in Norway and Sweden have declined at the same time that numbers in Finland have increased.

Whimbrel. Fennoscandian trend indicates a decline of 1.3 % per year. Whimbrel is doing poorly in Norway and Sweden but better in Finland. 

Wood Sandpiper. This widespread species has increased slowly (0.8% per year), a trend that is largely driven by Norwegian and Swedish populations.

blog wood sp

Wood Sandpiper was the second most commonly encountered wader

Redshank. The fact that no change was discernible, suggests that boreal and arctic populations are faring much better than the breeding populations further south in Europe. For example, see Redshank – warden of the marsh.

blog RK

Redshank – more obvious than most breeding waders encountered!

Spotted Redshank. The estimated annual decline for Spotted Redshank is 2.8% per year but the species is too thinly spread for this to provide significant evidence of a decline. This rate is very similar to the recent drop in the Wetland Bird Survey index in the UK. See Fewer Spotted Redshanks.

Broad-billed Sandpiper. This species has the second most negative trend among the 22 species analysed (-5.6% per year). The bulk of information comes from Finland where the trend is even more negative (-7.5% per year). Birds head southeast in the autumn to countries bordering the Indian Ocean – areas for which winter trend data are not available. The species is still considered to be of ‘least concern’ but perhaps this designation may need to be revisited?

Dunlin. Breeding birds in the survey area are largely of the alpina race. The overall trend is significantly positive (+4.1% per year), which is in sharp contrast to the strong declines of the schinzii subspecies that breeds around the Baltic Sea, western Finland and further south and west in Europe.

blog rnpRuff. There were major declines in the period immediately prior to this review (Lindström et al. 2015) but changes reported here are lower (-2.3% per year) and the decline is not statistically significant.

Red-necked Phalarope. The authors write, “This species has the most negative trend of all the 22 species [-7.9% per year], with most data coming from Sweden. We do not know the cause of this decline but, given that this species shares its south-eastern migration route with Broad-billed Sandpiper, whose population exhibits the second largest decline, the relevant problems might largely apply somewhere along the migration routes”.

Link to Britain & Ireland

As shown in Which wader when and why? there are strong migratory connections between Fennoscandia and the British Isles. Some waders, such as Green, Common and Wood Sandpipers, pass through on their way south in the autumn, whilst many more fly here for the winter, to take advantage of the warmer maritime climate.

Three wader species with particularly strong links between Fennoscandia and Britain & Ireland are still shot and eaten in these islands. Each autumn, large numbers of Woodcock, Golden Plover and Snipe cross the North Sea. It is difficult to ascertain figures for the number that are shot but there is agreement that the vast majority are winter visitors, as opposed to native birds. The results presented in the paper suggest that there have been no discernible changes in the Fennoscandian populations of these three game species in the period 2006-18. Two earlier WaderTales blogs focus on Woodcock and Snipe in Britain & Ireland:

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There has been no significant change in Golden Plover numbers across Fennoscandia

Two WaderTales blogs about wintering waders in Great Britain and the island of Ireland were published in 2019, based on reviews in British Birds and Irish Birds. These were Do population estimates matter? and Ireland’s wintering waders. The six big losers, in terms of wintering numbers in these islands, were Knot, Oystercatcher, Redshank, Curlew, Grey Plover and Dunlin. Knot arrive from Greenland and Canada, with Grey Plover flying from Russia, but it is interesting to think about this Fennoscandian breeding analysis in the context of winter losses of the other four species.

  • Wintering numbers of Oystercatchers have dropped recently in Britain and in Ireland. The population is made up of migrants from Iceland (more about this here), very large numbers from Norway, birds that stay within the British Isles and smaller numbers from other European and Scandinavian countries. Given there is no discernible decline in Fennoscandia, it seems likely that much of the decline can be attributed to a major fall in Scottish breeding numbers (more about this here).
  • Most Redshank wintering in Britain & Ireland are of local or Icelandic origin. Fennoscandian numbers seem to be stable; if there were any changes, these would probably not be apparent in wintering numbers within the British Isles.
  • The Eurasian Curlew has been classified as ‘near-threatened’ and the species is known to be declining in many areas (see this blog about serious problems in Ireland). Ringing shows a particularly strong link between Finland, where breeding numbers seem to be increasing, and Britain & Ireland. The decline in British and Irish winter numbers is probably being driven by lower breeding numbers within the British Isles and in countries such as Sweden, Norway and Poland.
  • There is a theory that new generations of alpina Dunlin may be more likely to winter within Europe’s mainland estuaries, instead of continuing their westward migration across the North Sea. This might explain the apparent anomaly between the 4.1% per annum rise in Fennoscandian numbers and recent winter declines of 3% in Britain and over 20% in Ireland.

Going forwards

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Some of the survey areas were in particularly remote areas

Many of the study squares that were covered during these surveys are a long way from the main centres of human population in Norway, Sweden and Finland. The governments of the three countries are to be congratulated for supporting this important monitoring, which relied on the commitment of hundreds of volunteers. It is to be hoped that these surveys will continue and that further species-focused work will be able to explain some of the differences across Fennoscandia, particularly between eastern and western areas. The rapid declines in numbers of two species that migrate southeast each autumn (Broad-billed Sandpiper and Red-necked Phalarope) highlights the need for better information about what is happening on the flyway linking Fennoscandia with the Arabian Sea and coastal countries of the Indian Ocean.

Paper

Population trends of waders on their boreal and arctic breeding grounds in northern Europe: Åke Lindström, Martin Green, Magne Husby, John Atle Kålås, Aleksi Lehikoinen & Martin Stjernman. Wader Study 26(3)

Click on the title of paper to access it on the International Wader Study Group website. Paper is only available to members of IWSG. If you have read the whole of this blog you’ll probably want to join!

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Nesting Bar-tailed Godwit in smart summer plumage


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.

 

 

Generational change

blog TGG on postIn a changing world, with more chaotic weather patterns and rapidly altering habitats, migratory birds are faced with opportunities and challenges. Long-term monitoring of colour-ringed Black-tailed Godwits, during a period of range expansion and phenological change, has revealed that individuals behave consistently over time but that the behaviour of new generations is moulded by the conditions they encounter.

A changing world 

When trying to explain observed changes in the distributions and annual cycles of migratory birds, there are many things to consider:

  • blog VM y flag

    Colour-rings enable life-time tracking. This bird, caught on its nest, had been ringed as a chick.

    Are individual birds able to take advantage of new breeding and non-breeding sites, as they become available, particularly if other areas become less suitable?

  • Are individuals able to change the timings and patterns of migration?
  • Do individuals adjust their migration routes as a consequence of changes in stop-over or wintering areas?
  • If individuals do not change what they do, how do we explain range expansions and changes in timing of migration?

Put simply, how does climate change lead to changes in distribution of migratory birds? Answering this question is key to being able to predict the rate and direction of future changes, and to assess whether our existing networks of protected sites will continue to support populations in the way that was intended. This issue was tackled by Jennifer Gill, José Alves and Tómas Gunnarsson in their paper “Mechanisms driving phenological and range change in migratory species”, published in Linking behaviour to dynamics of population and communities: applications of novel approaches in behavioural ecology and conservation, a special issue of Philosophical Transactions B (Royal Society).

Potential models

Change could happen in two main ways:

  • Individuals could relocate – having knowledge of a range of available conditions, they can choose to move elsewhere.
  • New generations could settle in new areas (in the breeding season, the non-breeding season or both) and/or adopt new migratory strategies.

blog map

Map that illustrates range expansion

Working out whether change happens through individual movement or generational shifts can only be done by life-long tracking of individuals, in populations in which range change is happening. The Icelandic population of Black-tailed Godwit is ideal for such an investigation. Black-tailed Godwits have been expanding into new breeding areas of Iceland for over 100 years, as discussed in this WaderTales blog. Population growth has been facilitated through warming spring conditions, as discussed in From local warming to range expansion.

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Naive youngsters, gathering together before migration

Icelandic Black-tailed Godwits fly south in the autumn, to spend the winter in the British Isles, The Netherlands, Belgium, France, Spain and Portugal. As numbers have grown, winter counts have increased in many areas, with new flocks appearing and expanding on estuaries and areas of wet grassland where the species was previously absent or scarce.

 

Winter distribution

The Wetland Bird Survey shows that there are three times as many Black-tailed Godwits wintering in Great Britain as there were 25 years ago. The biggest changes in numbers have occurred on estuaries in the northwest of England, with the Morecambe Bay winter maximum rising from about 180 to 3200, for instance. Where have these extra birds come from?

blog juvs on Axe

These young birds happen to have ended up on the Axe Estuary in Somerset

Black-tailed Godwits have been ringed in Iceland for nearly twenty years, providing a pool of known-age adults for which natal sites are known. Winter observations of colour-ringed individuals have shown an interesting pattern; birds breeding in newly-colonised areas, particularly in north and east Iceland, are the ones that are more likely to be found in newer winter sites.

In their paper, the authors suggest that birds nesting in these colder areas, where spring comes later, will be fledging quite late and leaving Iceland after adults have departed. With no experienced birds to follow, these young birds may well stop off at the first suitable site, many of which are in the north of the wintering range, and then they return to breed in their natal sites. Birds in Morecambe Bay don’t know that days are longer and the weather is kinder for other birds that travel further south to wintering areas such as Portugal.

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Wintering birds in Northwest England

Observations from birdwatchers show that the same colour-ringed individuals are nearly always found at the same wintering sites each year. Whatever mechanism is producing this new-breeding-site to new-wintering-site link, it is becoming clear that older birds continue to do what they have always done, with changes in distribution happening as a result of a generational shift.

The annual cycle

Colour-ringed Black-tailed Godwits have been tracked for over 25 years, with a small number of individuals contributing data for the whole of this period. This tracking information can be used to ask how much individuals move around and experience different sites and to assess whether individuals from different generations are using different parts of the range.

Using colour-rings, the Black-tailed Godwit team has discovered that, although individuals can live for over 20 years, in that time they generally use a total of only about four sites between leaving Iceland in late summer and returning in the spring. Basically, individual birds have very limited experience of sites and there is no evidence that they have moved to occupy different sites as, for instance, winter conditions have changed.

blog infographic

Spring arrivals in Iceland

Colour-ring observations have shown that individual birds do not change their breeding or wintering locations and that migrating individuals often appear in the same stop-over sites year after year. The timing of movements is also pretty consistent, especially in the spring. A previous WaderTales blog called Why is spring migration getting earlier? demonstrated that the timing of  migration of individual Black-tailed Godwits varies very little, with observed shifts in the period of migration being driven by young birds returning to Iceland for the first time on average doing so somewhat earlier than previous generations. Once individual birds settle into a timing pattern, they stick to it.

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Black-tailed Godwits, newly arrived in Iceland after crossing the Atlantic

Migration patterns

As discussed above, individual Icelandic Black-tailed Godwits have experience of only a small number of sites, which they use on an annual cycle. When migrating, a bird will generally use the same stop-over site when breaking its journey south, to undertake autumn moult, or on their way north, to take on fat for the trans-Atlantic journey. There is a range of spring migratory strategies in islandica Black-tailed Godwits, as discussed in Overtaking on migration.

blog wwrwOnce established, the annual migratory programmes of individuals rarely change, as illustrated by the map to the right. Colour-ringed Black-tailed Godwit W-WR/W regularly moulted on the Wash, in eastern England, before spending the late winter and spring in northwest England. In the late summer of 2002 he was reported at Slimbridge on 18th and 20th July but back on the Wash on the 25th. Having made the Atlantic crossing and ended up in southwest England, he was able to correct what he may have perceived to be his mistake, returning to the moulting area that he had been using since at least 1996.

Individuals might not change their annual migration routes but we do see changes in numbers on different sites that are used during migratory stop-overs. In a paper published in 2018, Mo Verhoeven and colleagues investigated whether observed changes in migratory patterns of a population of the limosa subspecies of Black-tailed Godwit were caused by individuals altering their strategies or by generational change.

Limosa Black-tailed Godwits leave breeding areas in countries such as The Netherlands in late summer, heading south to either West Africa or Iberia, where they spend the winter. In spring they all gather in staging sites in Portugal and Spain, typically on rice fields. Over the course of less than ten years, the average peak number in Extremadura (Spain) has dropped from about 24,000 to 10,000, while the numbers on the Tagus and Sado estuaries rose from 44,000 to 51,000. These changes took place during a period of rapid population decline, as described in this blog focusing on a paper by Rosemarie Kentie and colleagues.

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Limosa Black-tailed Godwits feeding in a rice field in the Tagus estuary

Mo Verhoeven et al have shown that this rapid population-level shift in spring stop-over sites from Spain to Portugal, 300 km further west, was driven by young godwits increasingly using Portugal in the period January to March, instead of Spain. Nearly all of the older birds stuck with the routes they knew. The paper is Generational shift in spring staging site use by a long-distance migratory bird.

Change happens to birds

One thing that is becoming clear in Black-tailed Godwits is that birds are being affected by change – individuals do not have the knowledge or flexibility to effect change. Even in long-lived birds, like Black-tailed Godwits, we see no evidence of individuals altering what they do over what is now two decades, despite the fact that the species’ migration dates, wintering areas and migration routes have all perceptibly changed over the same time period. It’s all about generational change. The behaviour patterns of young birds arise from the conditions they encounter in the first year of life, after which they are repeated.

Details of the Generational Change paper by Gill et al

blog LJ sum plumThe paper at the heart of this blog is: Mechanisms driving phenological and range change in migratory species by Jennifer Gill, José Alves and Tómas Gunnarsson, from the Universities of East Anglia (UK), Aveiro (Portugal) and Iceland. It is published in Linking behaviour to dynamics of population and communities: applications of novel approaches in behavioural ecology and conservation, a special issue of Philosophical Transactions B (Royal Society).

The paper could not have been produced without the help of “thousands of observers of colour-ringed godwits who have made these analyses possible”. This WaderTales blog is a celebration of the work they do: Godwits and Godwiteers.


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

 

Time to nest again?

blog Snipe TGGEarly return to breeding areas is widely acknowledged to be ‘a good thing’ but why? Some people suggest that early migrants can choose the best territories, others argue that early chicks have a disproportionately high chance of fledging but there are other explanations too. In their paper in Ecology & Evolution, Catriona Morrison and her colleagues ask how much of the advantage of being an early migrant could be associated with having an option to nest again, if the first attempt fails.

Setting the scene

In a previous WaderTales blog, about Icelandic Black-tailed Godwits, there is clear evidence that the species is increasing in number and spreading into new breeding areas. In another blog you can read that the expansion is linked to warmer spring conditions, which allow earlier nesting. How might this change in nesting phenology influence overall productivity and contribute to the population growth in Black-tailed Godwits, and do the same processes work for other species?

blog oyc godwit

Individual Black-tailed Godwits that arrive in Iceland early each year may have a higher chance of nesting successfully, just because they have time to try again if the first nest fails

In their 2019 paper, Catriona Morrison and her colleagues from the Universities of East Anglia (UK), Iceland and Aveiro (Portugal) used a simulation model to ask whether the greater time available for laying replacement clutches can create a pattern of increased productivity among early-arriving migrants, without the need to think about territory choice or local resource availability. They suggest that early arrival can lead to greater breeding success simply because early birds have more time available to nest again, following nest loss. Within the model they explore the effect on breeding success of varying several important relationships:

  • blog Snipe nest

    This early Snipe nest might get predated but there should be time to try again

    Whether early clutches are more likely to hatch than later ones (seasonal variation in nest survival rates) – such a trend could be created by predation patterns, resource availability and opportunities to conceal nests.

  • Whether one or more replacement clutches is possible within the time available during the breeding season (number of re-nesting attempts).
  • Whether late chicks are less likely to survive and become breeding adults than earlier ones (seasonal variation in recruitment rates) – which would make re-nesting attempts less valuable.

Results

The models developed for the paper showed that, when the chance of losing a breeding attempt does not change during the course of the breeding season, species experiencing intermediate nest survival rates will benefit most from re-nesting. This makes sense; a species that has a very high chance of hatching its chicks will not need to re-nest and one that has a negligible success rate is not going to do much better if it lays more than one clutch.

blog Lapwing

This late-nesting Lapwing may not be able to defend its nest

Nest success may not be constant over the course of a season. Late pairs may find it harder to distract predators if they don’t have the support of other breeding birds, with a consequent drop in success over the summer. Alternatively, species that nests in clumps of grass, such as Snipe, might find it easier to hide their nests later in the season, thereby increasing nesting success over time.

Picking out just a few of the scenarios that are covered in more detail in the paper:

  • When nest survival rates are constant and replacement clutches are possible, early arrival increases the probability of achieving a successful nesting attempt. These benefits of early arrival can be substantial enough to persist even when late-hatched chicks (from replacement nests) are less likely to survive and recruit into adulthood.
  • If there is a seasonal decline in nest survival, late-arriving individuals will have far fewer successful nesting attempts in their lifetime than early-arrivers. In this case, laying replacement clutches only slightly increases the number of successful nesting attempts and the subsequent number of recruits.
  • If there is a seasonal increase in nest survival, early-arriving individuals will tend to lose their first clutches but these individuals have time to re-nest, and are likely to fledge the subsequent attempt. Late-arriving individuals arriving will be more likely to have a successful first attempt and hence the number of successful nesting attempts varies little with arrival date.

The main take-home message of the paper is that, in almost all of the circumstances considered, early arrival can lead to higher breeding success, simply because of the greater time available to lay replacement clutches.

Blog RP migration

What does this mean for waders?

blog Oyc nest

An Oystercatcher does not need much time to ‘build’ a nest

Repeat nesting is a common strategy in waders; a female Oystercatcher, for instance, can quite quickly lay a second clutch if the first clutch is lost. Strategies exist that can lead to a female having more than one successful brood in a season, as seen when a female Dotterel leaves a male to incubate a clutch of eggs and moves on to another male. In most circumstances, however, a pair of waders has time to raise one brood of chicks in a season, by succeeding with the first attempt or taking opportunities to lay replacement clutches if time and resources allow.

It is obvious that, if nesting success is very high, there will be little need to lay a second clutch and if success is really low, little will be achieved by laying more clutches. Waders tend to have intermediate nest-success; most are ground-nesters, making them vulnerable to a wide range of mammalian and avian predators of eggs and chicks. The scenarios modelled in the paper are particularly (but not exclusively) appropriate to breeding waders

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Knot – a High Arctic breeder, constrained by a short season

The modelling used in this paper shows that having the time to try again is likely to increase the probability of annual success, as long as the breeding season is long enough. We know that pairs of Ringed Plovers breeding at temperate latitudes have time for several breeding attempts but pairs at high latitudes may have little chance for a second attempt, especially if nest failure occurs late in the incubation period. One way of increasing the time available to breed is to arrive earlier and the benefits of early arrival may be particularly strong for birds that occupy areas where there is a lengthening potential breeding season, something that can be made possible through climate change and warmer springs.

It is not uncommon for a breeding wader to live for five years, ten years – or even longer for larger species (WaderTales blog). During its lifetime, an individual may experience breeding seasons with differing levels of predator activity or other causes of nest loss, such as flooding or trampling, might occur. Although an individual might migrate at the same time each spring, the number of nesting attempts it will be able to fit in during any particular year will depend upon factors such as weather, prey availability and predation pressure.

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Sanderling with chicks

Nest survival rates in wader populations can show seasonal declines (e.g. Sandercock 1999 – Semipalmated Sandpipers), increases (e.g. Reneerekens et al. 2016 – Sanderling) or little seasonal variation in survival (e.g. Sandercock 1999 – Western Sandpiper), but in all cases there is variability between years. All of these seasonal patterns of survival change were modelled in the Morrison et al paper. In almost every situation, a wader will have a higher chance of successfully rearing youngsters if it (and its mate) are on an early spring migration schedule.

Summary

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This Oystercatcher may regret nesting early! If it fails, it can try again.

Turning up early on breeding grounds in spring can potentially lead to higher reproductive success, solely as a result of the greater time available for laying a replacement clutch. Using modelling, Catriona Morrison and colleagues show that this early-arrival-benefit can be conferred even when later nesting attempts are less likely to produce successful recruits.

Advances in the timing of spring migration are occurring in many species and these findings highlight the potential role of replacement nests as a driver of population increase in those areas where repeat nesting becomes increasingly possible. Professional ornithologists and citizen scientists who study nesting birds (not just waders) are encouraged to do so for the whole season, especially by following marked individuals. Birds that wear geolocators, which can record incubation patterns for nesting attempts that would otherwise remain undetected, may be particularly helpful when trying to discover just how likely birds are to re-nest and with what success.

Only part of the story

Blog tag

Geolocator on Whimbrel

In the long run, the success of an individual bird can be measured by the number of offspring it has in its lifetime and even by the number of its genes that are present in future generations. The number of chicks that fledge each year is only part of the story, therefore. How many of these youngsters recruit to the breeding population? Do they end up breeding in areas where they will have high breeding success? Will their progeny live for a long time and hence have many opportunities to produce their own chicks? Long-term wader studies might reveal some of these answers – eventually.

Paper

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The aim: a successful brood

The paper was published in Ecology & Evolution.

Why do earlier-arriving migratory birds have better breeding success? Catriona A. Morrison, José A. Alves, Tómas G. Gunnarsson, Böðvar Þórisson and Jennifer A. Gill.

DOI: https://doi.org/10.1002/ece3.5441

The paper is freely available to view.

 


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.

Whimbrel: time to leave

blog WW-WLGeolocators* have provided fantastic information about the movements of migratory birds – making links between countries, revealing previously unknown stop-over sites and indicating just how quickly birds traverse our planet. A small number of Icelandic Whimbrel have carried geolocators for up to six annual cycles, providing Camilo Carneiro with an opportunity to investigate the annual consistency of egg-laying, autumn departure, arrival in West Africa, departure in the spring, stopover in Western Europe and arrival back in Iceland.

* Geolocators are tiny devices that record the daily positions of birds, by measuring the timing of dawn and dusk. An individual typically carries a geolocator for a year and then needs to be re-caught for the data to be downloaded.

Planning a trip

When booking a train journey on-line, the first question I am asked is whether I want to stipulate departure time or arrival time.  In early spring, with breeding on their minds, you might think that Whimbrel will focus on the time they need to be in Iceland, rather than the time they leave West Africa? If that’s the case then it might be best to take early spring opportunities if they arise, to catch express winds that will make the journey as rapid as possible and to get to Iceland early. Is that the case?

blog mangroves and beach

The Whimbrel is one of several wader species that breed in Iceland. Each autumn, Redshank, Snipe, Golden Plover, Oystercatcher and Black-tailed Godwit fly south to Europe, especially Ireland and the United Kingdom, but many Ringed Plover, most Dunlin and most Whimbrel travel as far as Africa. The main wintering sites for Whimbrel are in West Africa, south of the Sahara, in countries such as Guinea-Bissau. Here they can be seen feeding on crabs on the mangrove-fringed muddy shoreline (above). It’s a very different environment to the inland floodplains of Iceland (below).

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In a paper by Tómas Gunnarsson & Gunnar Tómasson in 2011, we learnt that Whimbrel arrival times in Iceland did not change much between 1988 and 2009 (just 0.16 days earlier per year), while timing of arrival was advancing much more in species that travel less far to winter grounds, as you can see in this diagram.

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Changes in first spring arrival dates of six species of waders in southern Iceland from 1988 to 2009 (reproduced from Gunnarsson & Tómasson 2011).

The arrival date for Black-tailed Godwit was advancing fastest (0.81 days per year). In more recent research, it has been shown that the rapidly advancing trend for Black-tailed Godwits is being driven by new recruits to the population – individual adults are not changing their schedules. Why is spring migration getting earlier? summarises a paper by Gill et al in Proceedings of the Royal Society B.

The Whimbrel trend has been recalculated, with a longer run of years, and the new change of 0.03 days earlier per year is not significantly different from zero. Given that Whimbrel are breeding alongside other species that are arriving in Iceland much earlier than thirty years ago, what are the constraints to the timing of their migrations?

Migration timings for Whimbrel

Camilo Carneiro, José Alves and Tómas Gunnarsson from the Universities of Aveiro (Portugal) and Iceland have been studying a population of Whimbrel in Southern Iceland. Birds are caught on the nest in one year and then re-caught in the subsequent year – or two years later if a bird evades capture in the intervening summer. The following results summarise weeks and weeks of patient fieldwork and brush over the hours of frustration caused by wary birds that have been caught before!

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Over the course of the whole study, 86 Whimbrel were fitted with geolocators, 62 of which were retrieved. Repeatability could be calculated for 16 birds, with between 2 and 7 years of data collected from each individual. The results are summarised in these few bullet points. Please see the paper for confidence intervals and more details about differences between the sexes.

  • Blog tagIndividual timings of autumn departure from Iceland varied between years. The repeatability index is 0.28, with a suggestion of a gender difference (females 0.40, males 0.02). Males tend to look after chicks for a longer period than females so their departure dates may be more strongly influenced by the success of each year’s breeding attempt.
  • Autumn arrival time in West Africa was closely linked to departure time because, on all but one occasion, southward migration was achieved through a single direct flight. See Iceland to Africa non-stop.
  • Spring departure time from West Africa was highly consistent, with a repeatability index of 0.76 and no discernible difference in repeatability between males and females.
  • blog long green grassSpring arrivals in Iceland. Some Whimbrel that managed to complete spring migration in a single flight in some years stopped off in other years. These breaks, perhaps to wait for more helpful wind conditions and/or to refuel, resulted in variability in annual arrival dates for individuals. The repeatability for the two sexes combined was 0.23.
  • Laying date was the least consistent stage of the annual cycle, with a repeatability index of 0.11 and no significant difference between males and females.

In an individual Whimbrel’s annual cycle, there appears to be one fixed point – departure from wintering ground in West Africa. With no discernible seasonality of resource availability on the wintering grounds and little change in day length in these areas, departure dates are probably being determined by an ‘internal clock’. Two major unknowns will then determine what happens in the next twelve months. Will wind and weather conditions be conducive to a one-leg flight to Iceland and how successful will a bird be in any particular breeding season? Unforeseen events, such as having to wait for a delayed partner, losing a first clutch, and the time needed to guard chicks will all affect the timing of autumn migration.

Understanding individuals

blog tag through grassThe study of wader migration has advanced hugely.

  • Fifty years ago, the main measure of migration phenology was the appearance of the first individuals of a species.
  • Colour-ring sightings are ideal for providing repeat arrival dates over the lifetimes of individuals, as exemplified by the Gill et al paper on Black-tailed Godwits, which suggest that individual timing is highly repeatable.
  • Geolocators have provided more detailed information about the precise arrival and departure timings of individuals, which is so important if we wish to conserve threatened, migratory species that visit areas in which data collection was previously virtually impossible.
  • Now, by tracking individual birds for several years, it is possible to look at the variability in annual patterns, and what can cause this variability.

Over the next decade or so, as devices get smaller and remote downloads become easier (eg using GSM tags), it should become possible to understand the conditions that lead to fast, slow and aborted migratory journeys in a whole range of species. Exciting times!

Paper

Why are Whimbrels not advancing their arrival dates into Iceland? Exploring seasonal and sex-specific variation in consistency of individual timing during the annual cycle. Camilo Carneiro, Tómas G Gunnarsson & José A Alves. Frontiers in Ecology & Evolution.

There is more about the information that is obtained from geolocators, how they work and the affects that they have on the individual birds that wear them in these two blogs:

blog roost flock


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