UK Dotterel numbers have fallen by 57%

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

Male Dotterel brooding chicks: Alistair Baxter

Male Dotterel brooding chicks: Alistair Baxter

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

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

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

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

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

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

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

Population changes across the range

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

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

Is the SPA network working for Dotterel in Scotland?

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

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

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

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

Explaining the declines

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

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

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

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

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

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

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

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

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

What next?

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

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

Ptarmigan is another montane species that will be targeted by

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

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

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

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


 GFA in Iceland

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

@grahamfappleton

A helping hand for Lapwings

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

Lapwing in flight: Richard Chandler

Lapwing in flight: Richard Chandler

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

On the look-out: Grahame Madge/RSPB impages

On the look-out: Grahame Madge/RSPB impages

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

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

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

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

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

Lapwing chick: Richard Chandler

A young and vulnerable Lapwing chick: Richard Chandler

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

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

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

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

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

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

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

A weasel leaves its mark: Becky Laidlaw

A weasel leaves its mark: Becky Laidlaw

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

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

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

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

Update 

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

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

 


 GFA in Iceland

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

@grahamfappleton