25 years of wader declines

This article summarises a Bird Study paper arising from a 25-year Scottish study of breeding Lapwing, Oystercatcher, Redshank & Curlew. The story is set against a backdrop of a changing farming landscape.

RC LapThe interesting and sobering feature of this paper about breeding waders by Mike Bell and John Calladine is that its focus is a ‘normal’ area of farmland in Scotland. If you’ve taken the A9 north of Stirling, through Strathallan, then you’ll have driven past the fields. Perhaps you might even have noticed displaying Lapwing, Oystercatcher, Curlew and Redshank? Over a 25-year period, the number of breeding waders in this valley and another one that runs northwest and that can be seen from the B827 has dropped from 600 pairs to just 76 – that’s a loss of 87%, or over 20 pairs per year.

So, what has changed in this part of Scotland that might be linked to these declines? The authors conclude that the reduction in numbers can be linked to changes in field management. Put simply, there are too few bare fields in the spring for Oystercatcher (down 95%) and Lapwing (down 88%). These two species hide their nests in ‘plain site’; they watch out for predators, take off early and hope that the eggs are coloured cryptically enough to avoid detection. Having left their nests, they attempt to deter and/or distract prowling crows etc.  Redshanks (down 87%) and Curlew (down 67%) have also declined, even though they hide their nests in long grass, about which more later.

map graph

Lapwing declines in the Strathallan area are not that much different to those that have been charted across much of Britain & Ireland

In for the long haul

In a survey in the late 1980s, this area of Strathallan held an important assemblage of farmland breeding waders, with particularly high densities of nesting Lapwing. Land use in the valley is predominantly agricultural, with a mixture of arable fields and grazing by sheep and beef cattle. It is a relatively open landscape with few hedgerows, some scattered shelter belts and small conifer plantations.

KS RedshankThis study started in 1990, when breeding densities of nesting Oystercatcher, Lapwing, Redshank and Curlew in the core area were still high, at 11.7, 35.6, 4.7 and 3.3 pairs/km2 respectively. Unlike a PhD project, which might include three years of data, Mike Bell has kept this survey going for 25 years. Mike is the volunteer Regional Representative for the British Trust for Ornithology’s Perthshire region.

Breeding waders within a core area of 65 fields and a small amount of wet fen were surveyed annually from 1990 to 2015. The field sizes were small, by modern standards, with only five fields larger than 20 ha. An additional 1 km2 of lowland mixed farmland was surveyed in most years, 4 km2 of moorland rough grazing was surveyed in four years and another 5.3 km2 of enclosed and unenclosed rough grazing and moorland was surveyed at the beginning and end of the survey period only.

Land management and usage were recorded for each field on the first visit in April or early May. Spring sward height in each field was recorded as one of three categories: no vegetation, short (<10 cm) or long (>10 cm). These sward categories comprised the following field types:

  • bare – ploughed or tilled land with no emergent vegetation
  • short – managed grass for grazing or mowing for hay or silage, rough grass, rush pasture, spring arable, setaside/fallow.
  • long – managed grass, rough grass, rush/pasture, setaside/fallow, heath/moorland, marsh/wetland, unmanaged rank grassland and woodland/scrub.

Where to find waders in Strathallan

In the early 1990s, Strathallan supported around 36 Lapwing pairs/km2 across the core study area, which is comparable with some of the highest densities reported anywhere in the UK. During the 25-year study, as the numbers of Lapwing, Oystercatcher, Redshank and Curlew declined, an increased proportion of the remaining breeding waders became restricted to areas with fields classed as ‘bare’ in spring, while the greatest losses were in fields with ‘short’ and ‘tall’ spring sward heights (see figure).

graphic

Changes in breeding densities of waders in Strathallan, on fields with different sward heights

Breeding densities of Curlew were low throughout the study area and, although overall numbers declined, there was low power to detect statistically significant changes. There were different patterns of change for Lapwing, Oystercatcher and Redshank within fields of different spring sward heights:

  • The least marked changes were in fields with no vegetation in spring.
  • Fields with short swards showed the largest declines.
  • The tallest spring sward heights supported the lowest densities of the three wader species, with Redshank present generally at low densities in all vegetation categories.
UK BBS

UK-wide Breeding Bird Survey trends for Oystercatcher, Redshank and Curlew. BBS is organised by BTO in partnership with JNCC and RSPB.

A changing farmland landscape

Sward heights reflected changing farming methods. Looking at the fields in terms of cropping regimes.

  • The highest densities of Oystercatcher were in spring-sown arable crops.
  • Rush pasture was the most favoured field type for Lapwing and Redshank at the start of the study but the amount of this habitat declined during the study, as farmers created semi-permanent pastures for over-wintering sheep. When this happened, birds became more restricted in their nesting distribution.
  • By 2015, very few fields were still under a crop rotation of grass and spring arable, that would have delivered a mosaic of sward structures. By this time, half of the Lapwing pairs were nesting in just four fields.

Breeding success

The breeding success of Lapwings was estimated in five sample fields that could easily be observed from roads or tracks without disturbing the adults. Lapwing productivity was less than 0.60 young fledged/pair (the bench-mark for a typical stable population) in all but three years and it was less than 0.25 young fledged/pair in 14 of the 22 years. With very low recruitment rates, it is not surprising that the Lapwing is in decline.

There are several WaderTales blogs about Lapwings breeding in lowland wet grassland, including A helping hand for Lapwings. A full list of WaderTales blogs can be found here.

What is changing?

TGG Oyc

The changing fortunes of Oystercatcher are discussed in this WaderTales blog

Within a mixed arable-pasture farmland environment, bare field and short swards in spring appear to be important to breeding waders. Losses of these preferred habitats type don’t appear to fully account for the decline in numbers, however.

Alongside changes to farmland habitats, other potential factors that could have contributed to the decline of the wader population in Strathallan include an increased incidence of poor spring weather, increased disturbance (including from dog-walkers in some fields in some years) and an increase in predators. Mike Bell thinks that one of the reasons for a possible link between productivity declines and wet weather is that birds are nesting in sub-optimal (long) grass and hence more affected by wetter conditions. He writes about this and potential reasons for increased disturbance in an upcoming article in Scottish Birds. A link to the Scottish Birds article will be included when available.

Densities of avian predators increased in Strathallan during the study period, with higher breeding densities of Carrion Crow and Buzzard and an increasing frequency of bigger flocks of non-breeding crows. There was no detectable change in breeding success during the study but it is possible that nest success was already depressed by predation when the study commenced.

A relentless decline

GHH pictureAlthough previously identified as a good area for breeding waders, in a Scottish context, there is nothing unique about this Strathallan study area. It is good to see these issues explored in Bird Study, the BTO journal. I am sure that the editor, Ian Hartley, will have been pleased to publish a paper based on a nice mix of dedicated fieldwork and scientific analysis – that’s what the BTO is all about.  If you want to understand the (not yet fully explained) sad demise of breeding waders in Scotland, check out the figures in the paper. These show a relentless, 25-year decline in nesting densities across a range of habitats and some less-than-subtle changes in the way that fields are now managed.

Here’s a link to the paper:

The decline of a population of farmland breeding waders: a twenty-five-year case study by Michael V. Bell & John Calladine in Bird Study, 64:2, 264-273 DOI: 10.1080/00063657.2017.1319903


 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

 

 

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Black-tailed Godwit pairs – the importance of synchrony

How long does a godwit wait around to see if last year’s mate will turn up?

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Newly-arrived Black-tailed Godwits. Time for a wash & brush up and then off to territory?

Colour-ringing enabled Tómas Gunnarsson to follow the lives of pairs of Black-tailed Godwits nesting near his parents’ home in Iceland. In this world, that is ruled by timing and opportunity, the pairings, divorces and re-pairings could form the plot for a TV soap-opera. The studies turned into a fascinating Nature paper that was written up in The Telegraph newspaper. The two main characters were christened Gretar and Sigga  by the journalist but they’re more commonly known as RY-RO and RO-RO.

A tale of two godwits

post-bird

How long should this godwit wait for its mate?

2002: Colour-ringed Black-tailed Godwits RY-RO (red yellow – red orange) and RO-RO bred successfully in Laugaras, in the inland part of Iceland’s Southern Lowlands. Come the autumn, they left Iceland. The female (RO-RO) probably spent the winter in Portugal, although she was only seen there in later years, and the male (RY-RO) opted for the somewhat colder conditions of eastern England.

2003: Next spring, RO-RO arrived on territory on 6 May, before her mate. She cannot have known whether he was late or dead when she made the decision to move in with a new male, who was later colour-ringed as OR-OO.  When RY-RO arrived back a week later, on 13 May, he had to find himself a new female (GG-YO), who had been paired to a different male in 2002.

2004: Come the spring of 2004, RO-RO and RY-RO arrived at the same time and got back together.

dscn2241

Tómas Gunnarsson with one of the colour-ringed Black-tailed Godwits

This is only one story but it seems to illustrate that there are good reasons to nest with a partner that is well known to you. This could help to illustrate why individual godwits are generally very good at timing their arrival back on territory, to synchronise with their partners, as revealed in this Nature paper, published in 2005.

Gunnarsson, T.G., Gill, J.A., Sigurbjörnsson, Þ. & Sutherland W.J. (2004) Arrival synchrony in migratory birds. Nature, 431, 646-646. DOI: 10.1038/431646a

In the paper the authors described the return of pairs of Icelandic Black-tailed Godwits to Laugaras in the spring of 2003. Godwits generally arrive in Iceland over a one-month period, between mid-April and the middle of May.

pairs-map

Each line joins the wintering locations of a pair of godwits

On average, previously paired males and females in the study arrived within 3.1 days of one another, despite the fact that males and females from the same pair had spent the winter on average about 1000 km apart and that there is no evidence that any pairs had met at passage sites prior to crossing the Atlantic. Arrival synchrony seems to be related to mate retention, as the only divorces occurred in two of the three pairs that arrived more than eight days apart.

Synchrony in timing of arrival on the breeding grounds may be important for retaining a mate from the previous year and avoiding a costly divorce – but how it is achieved is a mystery.

Warmer springs

Tómas Gunnarsson and his father, Gunnar Tómasson, have been studying the timings of spring arrival in south Iceland of a range of species since 1988. In a 2011 paper in Bird Study they estimated that the timing of arrival of the first black-tailed godwit moved earlier by about 5.5 days per decade over that period. Here’s a link to the paper.

graphAs this advance in spring timing of migration was already happening when Tómas was making observations of the paired birds in Laugaras in 2003, we were all interested to see whether the schedules of marked birds would advance in similar ways. Interestingly, we have been able to show that the timing of arrival of individual Black-tailed Godwits is actually not changing at all. There is year-to-year variation in the dates on which individuals arrive, but no trend. Instead it is new recruits into the population that are driving the earlier migration. There’s a blog about this here.

Whilst there are processes in play that mean new recruits are migrating earlier than their predecessors, there must also be reasons why time-fidelity is important for individual birds. Perhaps synchrony increases the probability that individuals will be able to nest with the same mate in subsequent years? This is hinted at by the fact that godwits have been observed to re-pair with previous partners if opportunities present themselves.

Potential benefits of re-pairing with the same mate

For Black-tailed Godwits, not enough is known about the benefits of retaining the same mate. Given that divorce events are rare, it would be hard to measure any consequences for productivity – even if the nests were easy to find and youngsters easy to track – neither of which is the case. For the moment, all that is available is evidence of divorce and the possibility that females will not wait for males that are late.

nest-finding

Nests are well hidden

Black-tailed Godwits are long-lived birds, with breeding territories in which resources are generally predictably distributed, and a pair is likely to be familiar with local predator densities and distributions. Whilst one member of the pair is incubating the eggs, the other spends a lot of time looking out for potential predators, and this mutual protection may well confer benefits for the adults and the eggs. Perhaps knowing the behaviour of one’s partner is important during the incubation period?

The complexities of incubating eggs

If the daily routines associated with parental change-overs at the nest become established over time, might this be an important driver towards fidelity? Fast forward to a paper on shorebird incubation patterns, published in Nature in 2016 by Martin Bulla et al, which might provide some clues:

Unexpected diversity in socially synchronised rhythms of shorebirds Nature 540,109–113 (01 December 2016) doi:10.1038/nature20563

patterns

This actogram from the Bulla Nature paper creates some wonderful patterns

This paper is the result of a collaboration between Martin Bulla and 75 of his wader biologist colleagues, all happy to share data on nest incubation patterns which Martin then analysed. This resulted in an amazing data-set of 729 nests from 91 populations of 32 shorebird species, from which Martin was able to report remarkable within- and between-species differences in nest incubation rhythms.

This study suggests that energetic demands are not an important ecological driver of incubation bout length, but instead that pairs have developed idiosyncratic incubation patterns, possibly as an anti-predation strategy. Effectively, risk of predation, rather than risk of starvation, may have a key role in determining some of the variation in incubation rhythms. This means that species that hide their nests (and themselves) incubate for longer and change places less frequently.

ringo

Incubating Ringed Plovers change places frequently

Ringed Plovers, for instance, walk away from their eggs when a potential predator approaches and change places on the nest frequently. A male or female Redshank, on the other hand, will sit tight and brood for about six hours before exchanging with its partner. While partner A is hunkered down on the nest, partner B leaves the area, so as not to draw any attention to the pre-packaged protein that partner A is sitting on. If B is only going to return when A is ready for a surreptitious change-over then the activities of the two need to be well synchronised.

As the authors point out in the paper, although the context for this comparative study was diversity in biparental incubation, it is possible that diverse behavioural rhythms may also arise in other social settings (for example, in the context of mating interactions or vigilance behaviour during group foraging). These are other circumstances in which it may well be beneficial to know one’s partner.

What does this mean for RY-RO and RO-RO?

Perhaps fidelity and synchronicity are really important to Black-tailed Godwits? If only their nests were easier to find and nest success was easier to measure! For the moment, all that we know is that pairs of Icelandic Black-tailed Godwits are remarkably synchronous in their arrival times on breeding territory, and something important must have driven the evolution of such a finely tuned migratory strategy.


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

Prickly problems for breeding waders

Spoiler alert – hedgehogs are the killers

Machair thinner (JC)

Hedgehogs – an unwelcome addition to the unique machair habitat  (Photo: John Calladine)

The chain of Hebridean islands from the northern tip of North Uist to the southern tip of South Uist are special places to visit in the summer. Nowhere else in the UK will you find higher concentrations of breeding waders. In 1983, Fuller et al. estimated that this region held a third of the UK’s breeding Dunlin and a quarter of its Ringed Plover. (Populations of breeding waders and their habitats on the crofting lands of the Outer Hebrides)

Catley Hedgepig

Photo: Graham Catley

The islands are still special but, as a consequence of the spread of hedgehogs, following the introduction of just four individuals in 1974, numbers of breeding birds have dropped dramatically. The addition of this extra predator, which can feed by day and night and possesses a coat of spines that can withstand aerial attacks by parent birds, has long been associated with the decline.  But how much of the blame lies with the hedgehog and what can be done to support wader populations?

Brief history

close up RP TGG

A quarter of the UK’s breeding Ringed Plover nest within the Outer Hebrides (Tómas Gunnarsson)

The Outer Hebrides, in north west Scotland, used to be a haven for breeding waders, many of which nest on machair, fertile coastal grasslands along the west coast.  It’s a mosaic of habitats that includes arable and pastoral farmland, pools and sand dunes. The waders that nest here have been subject to predation, from gulls, corvids, rats etc. but the hedgehog was an unwelcome addition. With no foxes or badgers to eat them, no fleas to carry diseases and a good supply of easily-accessible eggs, hedgehogs have thrived and spread.

Work in 1998, led by Digger Jackson, showed that the hatching success for Dunlin, Lapwing, Redshank and Snipe clutches was 2.4 time higher in areas from which hedgehogs had been excluded. This was published in the Journal of Applied Ecology in 2000.

Breeding waders were surveyed in 1983, when hedgehogs were restricted in their distribution to small parts of South Uist. By the time of the next extensive survey in 2000, hedgehogs were well-established across South Uist and Benbecula, and the first individuals had reached the southern end of North Uist Uist. In just 17 years, numbers of breeding waders declined by 39% in the areas with hedgehogs, while there was an increase of 9% in North Uist. There were differences for all wader species but particularly for Redshank and Lapwing. The results were published in Biological Conservation in 2004. A subsequent control programme, to assess whether eradication might be a practical option, was expected to arrest the decline in wader numbers and promote recovery. Sadly, population levels have not recovered as well as expected which begs the question – ‘are hedgehogs the only problem?’

Further large-scale surveys were carried out in 2007 and 2014

Walking transect cropped (JC)

Rob Fuller, walking a transect (John Calladine)

The 2007 survey is written up in Bird Study. (Changes in the breeding wader populations of the machair of the Western Isles. Scotland, between 2000 and 2007).

The 2014 survey is written up in Scottish Birds (Calladine, J., Humphreys, E.M. & Boyle, J. (2015). Changes in breeding wader populations of the Uist machair between 1983 and 2014. Scottish Birds 35: 207-215).

In the period between 1983 and 2014, the greatest overall proportional declines were of Dunlin and Ringed Plover (72% and 70% respectively). Snipe declined overall by 45% and Lapwing by 14% while, in contrast, Redshank increased by 8% and Oystercatcher by 74%. The changes were not the same in the zones with and without hedgehogs. The deviation in trends was most marked for Redshank (which increased by 91% in the northern zone, with fewer hedgehogs, while decreasing by 22% in the southern zone) and Snipe (much bigger decreases in the south). Dunlin and Ringed Plover declined markedly in both zones, though less so in the northern zone. Any difference in trends was less apparent for Lapwing, although it did appear that they may have fared less well in the southern zone.

Are hedgehogs the main problem?

Predation event 1 (SNH video grab)

A hedgehog ignores nest defence efforts of pair of Lapwing (screen-grab from SNH surveillance camera)

A recent report, prepared for Scottish Natural Heritage by a consortium comprising the British Trust for Ornithology, the James Hutton Institute and MacArthur Green Ltd., aims to quantify the importance of predation by hedgehogs, relative to that by other predators.  The report includes a summary of the changes in numbers for the various wader species during a forty-year period, based on occasional broad-scale surveys and more regular monitoring of specific study sites.  The focus, however, is on results from studies using nest cameras, temperature loggers and fixed point observations in the 2012, 2013 and 2014 breeding seasons, measures of disturbance, transect work to assess productivity, and some land use and habitat recording.

report coverCalladine, J., Gilbert, L., Humphreys, E.M., Fuller, R.J., Robinson, R.A., Littlewood, N.A., Mitchell, R.J., Pakeman, R.J. & Furness, R.W. 2015. Predation studies on breeding waders of the Uist machair: Final report covering fieldwork undertaken in 2012-14. Scottish Natural Heritage Commissioned Report No. 811. 

 

Hog on machair (JC)

A hedgehog in the half-light (John Calladine)

The principal aim of the study was to quantify the importance of predation by hedgehogs, relative to that by other predators, work that could support arguments in favour of continued and enhanced removal of these introduced predators. Cost-effective solutions may require lethal control, instead of or in addition to translocation. These are tricky decisions, especially when considered alongside the rapid decline in numbers of hedgehogs across much of the UK.

Main findings

survival table

Clutch survival rates

The latest study provides further evidence that predation by hedgehogs is having an ongoing impact on breeding success of wader nest on the Uist machair, at least some of which is additional to that of gulls, which take both eggs and chicks.

In North Uist (low density of hedgehogs) clutch survival rates were higher than on South Uist (high density of hedgehogs) for the four main study species – see table. Overall, in North Uist, 74% of

predation table

Confirmed and probable causes of predation

wader nests, where outcome was confirmed, successfully hatched chicks.  In South Uist only 45% of nests successfully hatched chicks.  Most observed losses in both areas were due to predators.

Hedgehogs were the most numerous nest predators identified using nest cameras and other evidence, accounting for over half of occurrences, with all confirmed instances of predation by hedgehogs occurring in the ‘high hedgehog density’ areas. In these high density areas, hedgehogs were responsible for 35% of nest failures. Although summer nights are shorter than in much of the UK, 45% of clutch incubations ended during darkness in high hedgehog density areas, compared to 29% in low density areas, again suggesting that mammals are the main predators, with hedgehogs the most likely culprits.

Predation event 2 (SNH video grab)

This Common Gull takes an egg – and may be back for more (screen-grab from SNH surveillance camera)

Although avian predators (gulls, raptors and corvids, which are diurnal predators) were recorded most frequently in the high hedgehog density areas, observers did not find a difference in the frequency of predation attempts by avian predators between these areas and areas with fewer hedgehogs. The number of successful attacks by avian predators witnessed during fixed point observations was small (24 in 460 hours of observations spread over three years) and more successful avian predation events were recorded in low hedgehog density areas (n = 15) than in high hedgehog density areas (n = 9), despite lower abundance of avian predators in the low hedgehog density areas. There is a suggestion that avian predation may, to some extent, replace hedgehog predation in areas with low hedgehog density, especially at the chick stage, but this interpretation is based on a small sample size.

Other potential causes of wader declines may be associated with land use changes within the machair. These are discussed in a 2014 Bird Study paper by Calladine et al.

Conclusions

hog-predated nest (David MacLennan)

Evidence of hedgehog predation (David MacLennan)

It is pretty clear that hedgehogs are causing significant problems for nationally and internationally important populations of breeding waders, two of which are red listed species of conservation concern (Lapwing and Ringed Plover) and the rest of which are amber-listed.  It is also clear that efforts to control hedgehogs have had limited success.

Eradication is a contentious issue. Hedgehogs may have been introduced but, having become established on the Uists, the species has attracted significant support from a number of animal protection organisations, members of which don’t want lethal control methods to be employed. Translocation – the current control method – is a costly alternative.

SNH has demonstrated a political will to try to tackle the hedgehog issue and has applied to the EU for funding for an eradication programme. There’s more about the Uist Wader Project  on the Scottish Natural Heritage website.

Given current financial constraints, EU funding seems to be the most likely way to deal with this man-made predation issue. Any eradication programme may rely on proving that translocated hedgehogs survive. If they don’t, then there is probably a choice between using lethal control or further losses of red-listed and amber-listed wader species. At that point, is there going to be the political resolve to embark on a plan to remove all of the hedgehogs? Wader biologists hope that funding can be found to tackle this prickly issue.


 GFA in Iceland

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

@grahamfappleton

Introducing WaderTales

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

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

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

Photo: Tómas Gunnarsson

Photo: Tómas Gunnarsson

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

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

Comments and suggestions will always be welcome.

Graham Appleton

GFA in Iceland