Scotland’s Dotterel: still hanging on

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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.

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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.

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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.

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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.

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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

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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.

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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).

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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.

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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.).

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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.

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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.

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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

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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

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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).

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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.

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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.

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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.

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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. 

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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.

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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. 

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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.

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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.

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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.
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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?

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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.

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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?

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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:

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    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.

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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.

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What does this mean for waders?

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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

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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?

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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

 

 

 

January to June 2019

blog CU postOne or two WaderTales blogs are published each month. The series is UK-based with a global reach. Suggestions of newly-published research on waders that might be of interest to birdwatchers who appreciate waders/shorebirds are welcomed. I am particularly keen to give feedback to colour-ring readers; they provide a huge amount of information that lies at the heart of these stories.

Click on a link in bold to read an individual blog.

You can sign up to receive an e-mail notification when a new blog is published.


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.

Managing water for waders

blog L sittingYour task, should you choose to accept it, is to turn farmland into a haven for breeding waders. The only tools you have at your disposal are tractors and cows and we will give you permission to pump water out of nearby rivers when conditions allow. That’s how it started. These days the diggers look big enough to use on a motorway construction site!

If your aim is to maximise the number of pairs of breeding waders on your lowland wet grassland farm or nature reserve, then one of the key issues is to get the water levels right. The first  part of this blog focuses on providing an appropriate mix of ditches, pools and grazed grassland for species such as Lapwing, Redshank and Snipe and then keeping everything wet enough (but not too wet) during the important chick-rearing season.

The second part of the blog is not just about maximising the number of breeding waders on a nature reserve. It’s also about working with neighbouring farmers, in order to secure fresh water supplies for the future and to reduce the risk of salt-water inundations, associated with sea level rise. In the long-term, stakeholder engagement has proved far more important than habitat management, as you will read below.

Understanding water levels

When developing lowland wet grasslands for waders, an extra five cm of late-winter rain can make a huge difference, especially if you can capture as much as possible of the rain that falls or can draw water from a swollen river. Mark Smart, the Senior Site Manager for the RSPB’s Berney Marshes and Breydon Water reserve in East Anglia, understands grazing marshes and how to capture and distribute water, in order to provide the muddy edges where wader chicks find insects. An aerial photograph of Berney Marsh shows how Mark has designed a special landscape to capture winter rain – one that is ideal for Lapwings and other waders.

Mark has taken the lessons he has learnt on RSPB nature reserves and shared them widely, a contribution to conservation that earned him one of the 2018 Marsh Awards for Wetland Conservation from the Wildfowl & Wetland Trust.

From wheat and barley to ducks and waders

blog cow eatingThe marshes of the Norfolk Broads have been drying out for 2000 years. By the 1970s, and after over 400 years of farming, the Halvergate Marsh complex was on the point of being fully drained and by 1985 much of the wet grassland in which waders formerly bred had already been lost and turned into arable fields. At this point, the RSPB made its first purchase of land, as they tried to retain at least some of the threatened habitat which is so important to winter wildfowl and summer waders. At the same time, campaigning by local and national conservationists secured legal protection for the unique Broadland scenery and the species that rely upon the habitats it contains, thereby halting the advance of the combine harvesters.

The importance of Halvergate Marshes for wildlife has long been known, and in 1987 it became the site of the UKs first Environmentally Sensitive Area – the prototype for subsequent agri-environment schemes. Lowland wet grasslands are traditionally drained using ‘footdrains’ – narrow, shallow channels that connect low-lying parts of the fields with surrounding ditches, in order to drain them.

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The muddy edges of a footdrain

These same footdrains can be used to hold and manage surface water levels within fields, by blocking the ditch connections with sluices. In the 1990s, Mark pioneered the design and deployment of footdrains on lowland wet grasslands, and the kit needed for their construction. Through his skills, enthusiasm and collaborations with grassland managers throughout lowland England, footdrains and the water that they can contain are now a common sight. Many generations of wader families have enjoyed the invertebrate food that footdrains support.

The breeding season for waders is very short – with the first Lapwing claiming territories in March and most chicks fledged by the end of July. Outside these months, these wet grasslands provide excellent grazing for geese and ducks in the winter and cattle in the summer. The task of nature reserve managers is to work with graziers to try to ensure that cattle deliver appropriate sward heights for winter wildfowl and summer waders.

Not just water

fence 2By creating a hot-spot for nesting birds, within an intensively-farmed landscape, land-managers also produce a food-rich area for predators, attracted in by concentrations of eggs, chicks and sitting adults. Restricting the activities of species such as foxes and crows is an important part of the role of an RSPB warden, carried out through site management and active control measures. By focusing these activities in the winter period, the RSPB’s Halvergate Marshes team are able to stop corvids and foxes from setting up territories within the area that is managed for breeding waders. Electric fencing can help to prevent foxes moving onto the site in spring, while changing the way that core wader areas are managed helps to reduce fox/nest interactions by, for instance:

  • Adding shallow ditches in the right places can break up the site into compartments and reduce the likelihood that nests will be predated.
  • Leaving areas with long grass, that is good for small mammals and the mustelids and foxes that prey upon them, can change the focus of hunting activities.
  • Erecting temporary fencing, during at least the early part of the nesting season, can both provide protection and potentially increase the synchronicity of nesting attempts and hence the ability of birds effectively to mob predators.

blog L chickThere is more about these measures in these blogs, with links to papers from the RSPB and University of East Anglia team of conservation researchers:

There is annual management of the Berney site too, with foot-drains to be re-cut, spoil to be spread in ways that can provide a mix of water-levels and more muddy edges, and rotovation of some areas to increase the diversity of habitats. These techniques might seem rather different to the ones that are used by farmers but many of the other operations at Berney are the same as would be seen outside nature reserves, with fences to mend, stock to manage and creeping thistle and rush to ‘weed-wipe’.

blog rotovation

Rotovation, carried out in dry conditions, adds heterogeneity and creates bare, muddy areas

Measuring success

The development of Berney Marshes has been hugely successful. Back in 1987, there were only 13 pairs of wader breeding on the site – nine pairs of Redshank and four of Lapwing. The total for 2019 looks like being about 270 pairs – over twenty times as many.

blog RK graphRedshank: The graph alongside illustrates how Redshank numbers have changed across the decades. At the same time as Breeding Bird Survey (BTO, JNCC & RSPB) for England results revealed huge declines, with a loss of nearly half in the period 1995-2017, Redshank pairs on Berney Marshes have been increasing. Even on this site, there is a suggestion that the peak number of pairs may be in the past. Given the pressures on breeding Redshank on saltmarsh habitats (blog: Redshank – the ‘warden of the marshes’), providing breeding habitat in coastal marshes, inside sea-walls, may be particularly important. Hopefully, the latest earthworks (see later) will create more space for Redshank.

Left image below shows Redshank nest in a clump of grass. The right image shows a Lapwing nest in a newly-rotovated patch. 

 

blog L graphLapwing: Between 1988 and 1998, the number of pairs of Lapwing rose from 14 to 79, reaching a peak of 157 in 2010. Numbers vary, according to spring weather and water levels, with between 83 and 130 pairs in the years 2011 to 2019. The national decline in England was 28% between 1995 and 2017 (Breeding Bird Survey) – not quite as drastic as for Redshank but still worrying. Intensive studies at Berney have shown that productivity is only high enough to boost numbers in some years. The latest project by UEA and RSPB conservation scientists involves trialling temporary electric fences to provide protection for first clutches and broods. Hopefully Berney can become a net exporter of Lapwings in most years.

Oystercatcher: There were no Oystercatchers breeding at Berney back in 1997. The peak number of pairs was 18 in 2009, with an average of ten pairs in subsequent years. Nationally, numbers in England have increased but with major declines in Scotland, which is the species’ heartland within the UK. This is discussed in an earlier WaderTales blog.

Avocet: The RSPB’s logo species has been hugely successful, nationally, with the help of protection and habitat creation. The first pair of Avocets bred at Berney in 1992 and pairs have bred in most years since then, with over thirty pairs in nine years but no pairs in 2013 or 2014. The 2019 count is 35 pairs and there is potential for further growth in numbers across the site, with the creation of more island homes (see below).

blog combine AV

Combined harvesters have been replaced by nesting Avocets

Snipe: Despite all of the excellent habitat creation work, there have never been more than 8 pairs of Snipe recorded on Berney and only between 0 and 3 pairs in each of the last ten years. The underlying soils at Berney are clay-based, which may not suit this species.

Sharing the knowledge

blog RK ringed

Redshank chick: science is an important feature of the work at Berney

Although it’s great that the RSPB has been able to buy and develop land for breeding waders in the Yare Valley, the impact of their work has been far larger, thanks to management agreements with other landowners. Mark Smart and the RSPB have set up Broads Land Management Services, to deliver wet grasslands that attract the top tier of conservation payments for farmers working in the Broads. Much of the recent work has been part of the Water Mills and Marshes Project, funded by HLF and led by the Broads Authority. Using specialist ditch-cutting and spoil-spreading equipment, the team has been able to create wet features within top-quality grazing fields. This is not just a local initiative; the kit and the advice have had impacts on farms and nature reserves across the country.

For his work for wetland conservation, Mark Smart received a Marsh Award for Wetland Conservation from the Wildfowl & Wetland Trust in 2018. “Mark Smart received his award for his 17 years managing RSPB Berney Marshes in the Norfolk Broads. Over this period, he brought together landowners, conservationists, local authorities and scientists to improve the marshes for wildlife. Today more than 300 pairs of wading birds nest there each spring, and more than 100,000 waterbirds return to it each winter.”

blog somerleyton

Illustrations above shows work that has been completed at Somerleyton in Suffolk and a newly-fledged Lapwing.

blog DutchWorking with his wife, Jen Smart, who is a Principal Conservation Scientist at the RSPB’s centre for Conservation, Mark has added a Dutch dimension to the RSPB’s advice work by co-authoring Meadowbirds on the horizon of southwest Friesland.  This report has just been published by the International Wader Study Group.

Climate – ‘the new normal’

Fresh water is an increasingly important commodity in East Anglia – for farmers and for nature reserve wardens, looking to maximise agricultural and wader chick production. More extreme weather patterns are already producing periods of drought and intense periods of rain, while a rising sea-level is increasing the salinity of rivers and limiting extraction opportunities. Broadland farmers are looking for a reliable water supply, the Environment Agency is looking for ways to reinforce sea defences and for places to store fresh water, in order to avoid flooding, and the RSPB wants to hold more water in the late winter that can be used to keep areas wet in the early summer. With some lateral thinking, many of the needs of these key stakeholders can be met in partnership projects, as shown below

The Environment Agency’s need for material to raise sea defences provided Mark Smart with an opportunity to provide more pools and scrapes for breeding waders. It was a win-win solution; free habitat creation work for the RSPB and minimal movement of the clay and top-soil that the Environment Agency needed. In the images below, you can see this work in progress and the islands that are now being used by nesting Avocets.

blog defences

The most recent project is an ambitious water storage and flood reduction scheme for the whole of Halvergate Marsh. This will keep salt water out of these important grazing marshes and store fresh water for summer use. The £2 million Halvergate Marshes Water Level Management Improvement Scheme is a joint initiative, funded by DEFRA and delivered by the Water Management Alliance. The project involves a large number of stakeholders, including the Broads Internal Drainage Board, RSPB and neighbouring farming estates.

blog 8 km

The Water Level Management Improvement Scheme is a huge undertaking, with 8 km of new ditches, 240 piped culverts and 12 big sluices, that will create storage for 60,000 cubic metres of fresh water and systems to distribute this water over the course of a dry East Anglian summer. One of the most impressive features of the project, illustrating the imagination of the design team, is the Higher Level Carrier, a ‘flyover’ ditch system that passes over the top of existing wet grazing land to get water to some of the driest part of Halvergate Marshes (left picture below). This high-level water transportation route was constructed using locally-sourced clay, thereby creating shallow pools around which yet more waders are already nesting.

blog overpass

When designing this project, the opportunity was taken to develop opportunities for birdwatchers to see the birds that will be drawn into the wettest areas, by making sure that the ‘best bits’ are close to public access points on the Weavers’ Way, the 61 mile (100 km) long-distance path running from Cromer to Great Yarmouth.

Aspirations

Mark Smart has not finished yet! Plans are afoot to develop the RSPB’s land that is closest to Great Yarmouth, recently purchased using a WREN grant. If agreed, this can provide an alternative, safe high-tide refuge area for tens of thousands of waders and wildfowl that roost on the mud and saltmarsh at the mouth of the Yare. Their current high-tide refuge is threatened by sea-level rise and developments proposed for the outskirts of Great Yarmouth.

blog aspirations

This proposed roosting area will be part of an extension to the Halvergate Marshes Water Level Management Improvement Scheme, which will add another 10,000 cubic metres of water storage. Alongside flood alleviation and fresh-water conservation, this scheme will create fifty hectares of additional shallow wader and waterfowl scrapes adjacent to Breydon Water.

blog Wood spThe new scrapes should not only attract wintering and breeding birds but also many passage waders, such as the Wood Sandpiper pictured to the right. The whole scheme has the potential to be another win-win-win-win, for the owners of low-lying properties, for Broadland farmers, for internationally important bird populations and for local and visiting birdwatchers.

Read more

Information about the RSPB’s Berney Marshes & Breydon Water reserve can be found on the RSPB’s website. Click here

There is information about the Water, Mills and Marshes project here.

blog AV


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

 

Chicks and ticks

How do ticks affect Golden Plover chicks? pic chick on moveBy utilising data from an existing study, David Douglas and James Pearce-Higgins have discovered that Golden Plover chicks that carry more sheep-ticks Ixodes ricinus have a lower chance of survival. Their findings are written up as a paper in Bird Study. The work is only based on a small sample and the data don’t identify the mechanism that leads to increased mortality but, given the current interest in the biological effects of ticks, the findings are interesting.

Costs of carrying ticks

Carrying ticks has three potential effects on wader chicks

  • Ticks suck blood, which could be costly.
  • Ticks can introduce diseases, via tick-borne bacteria and viruses.
  • There may be effects on feeding efficiency, via impaired vision, hearing etc.

Sheep ticks act as vectors for a variety of pathogens, including the louping ill virus (LIV) which can affect a range of domestic and wild mammals, as well as wild birds. LIV is known to cause high mortality of Red Grouse chicks but there has been no previous assessment of the effects of sheep ticks on other moorland birds, such as breeding waders. It should be noted that wader chicks eat ticks – so they are not ‘all bad’.

pic ticks

Ticks can clearly be seen on the unfeathered lower eyelid of this young chick. There are smaller ticks attached to the gape at the base of the beak as well.

All sorts of things could influence the probability of tick infestation in birds:

  • Ticks may be able to survive better in warmer conditions.
  • Tick numbers can be affected by the number of mammalian hosts.
  • Mammal to bird transfer could be affected by land management and habitat structure.

Ecological interactions between ectoparasitic ticks and waders are not well understood. Given possible increases in tick abundance with climate change, the authors of the new study felt that it would be useful to test whether ticks have detectable effects on the Golden Plover chicks that carry them.

Spotting an opportunity

The Golden Plover chicks that provided the data used in this paper were caught as part of a wind farm study at Gordonbush in northern Scotland, a site made up of 33 km2 of blanket bog. There is more information about the study in these two papers:

pic habitat

Gordonbush, prior to the development of a wind farm

Tick numbers on Golden Plover chicks were collected at the time of ringing (within 24 hours of hatching) and during subsequent recaptures. Recapture was facilitated by locating tagged birds using radio-location. On each capture, chicks were weighed and the number of ticks visible on the bare parts of the head (around the eyes and bill) were counted. Most ticks attach themselves to the bare parts of the head and neck.

Variation in tick loads on Golden Plover chicks

pic nesting ad

Incubating adult. Golden Plovers commence primary moult at the start of (or before) incubation. Read more here.

The number of sheep-ticks found on these Golden Plover chicks was higher than those previously reported for waders but were within the range of those found on Red Grouse on moorland. Previous wader studies had been focused upon areas with sheep, which were routinely treated to reduce tick infestations. In the current study it was found that:

  • 90% of chicks were carrying ticks, with between 1 and 12 ticks being found on each affected Golden Plover chick. The highest tick-load was found in mid-age chicks.
  • Tick loads were higher during periods with warmer maximum temperatures and when chicks were estimated to have moved through taller vegetation between recaptures.
  • Chick growth rates were depressed by high tick-loads, especially when temperatures were warmer.
  • Of the 21 chicks, 4 fledged, 13 died and the outcomes for the other 4 were unknown. Half of the deaths appeared to have been due to predation and half to starvation/exposure.
  • Chicks that were heavier (for their ages) were more likely to survive. Those with higher tick loads (for their ages) were less likely to survive.

With the small sample size, it was not possible to detect a correlation between tick load and chick growth rates but low survival was correlated with high tick-loads. This had not previously been documented for waders.

Implications for wader conservation

pic red deerGordonbush is an area where there is no grazing by domestic animals so the likely mammalian tick-hosts are Red Deer in particular and also Mountain Hare. The correlation between warmer weather and tick numbers, found in this study, could be explained by increased tick activity, while the link to taller vegetation may well be explained by ticks seeking damper microhabitats. In their discussion of the results, the authors suggest potential ways that ticks and waders, of different ages, might interact. Anyone looking to expand the work, in order to understand the mechanics of tick infestation, is likely to spend more time looking at ticks than waders!

pic Curlew

Could ticks be reducing survival probabilities for  young Curlew?

The authors of this paper were not able to test for the presence of disease (such as LIV) in their Golden Plover population but this is a plausible cause of the increased probability of mortality. In a study in Yorkshire by Newborn et al. (2009), no evidence was found of LIV in wader chicks, whereas it was present in 3.6% of a sample of Red Grouse chicks at the same sites. Newborn and colleagues report that a single Eurasian Curlew chick has previously been recorded to be seropositive for LIV. In the Newborn study, the lowest incidence of ticks among waders was in Lapwings (6% of broods), followed by Golden Plover (47% of broods had ticks) and Curlew (91% of broods). There is a hint, in these data, that ticks might more commonly attach themselves to wader chicks that are found in taller vegetation.

Despite high tick loads on chicks, and the correlation with lower chick survival, the overall percentage of Golden Plover chicks known to fledge in the Gordonbush study (19%) is comparable with other studies. Perhaps ticks are only causing the deaths of chicks that would have died anyway?

pic Red GrouseThe authors suggest that no case should be made for tick-control, to help breeding waders, until it is clear whether tick-based chick mortality limits Golden Plover and other wader populations on moorland. In the paper, they argue that previous attempts to reduce moorland tick abundance and tick loads on Red Grouse have failed to detect convincing evidence of improvements in grouse survival, breeding success or post-breeding densities.

A range of methods have been deployed in attempts to reduce moorland tick abundance and tick loads on Red Grouse, including reducing densities of mammalian tick hosts (Mountain Hare and deer) and deploying acaricides (as used in sheep dips). See this link to material from GWCT on ticks and Red Grouse.

In conclusion

pic older chickWork at a single site over two years appears to have documented a level of tick infestation in Golden Plovers that is associated with chick mortality. It is not clear how chicks are being affected, particularly given that there is insufficient evidence thus far that ticks affect chick growth rate.

The authors collected the data analysed in this paper for other studies – the focus was not on tick effects – and they hope that funding might be found for future research focusing upon the associations between ticks and waders, other birds and other animals. Until that happens, it would be useful if shorebird biologists who repeatedly handle wader chicks, in order to measure growth and survival rates, could routinely record the presence or absence of ticks.

Given that warming temperatures could lead to increased tick abundance, this seems to be a good time to discover more about tick behaviour, the importance of ticks as a food source for wader chicks and whether tick-loads are reducing growth rates and fledging success in other wader species.

Paper

This research is published in the BTO journal Bird Study. Click on the details below to link to the full paper:

Variation in ectoparasitic sheep tick Ixodes ricinus infestation on European Golden Plover chicks Pluvialis apricaria and implications for growth and survival. David J. T. Douglas and James W. Pearce-Higgins. Bird Study. June 2019.

pic bottom


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