BTO - British Trust for Ornithology - Marine

Leakage of plastics and other debris from landfills to a highly protected lake by wintering gulls

VIOLA.ROSS-SMITH — Fri, 26 Jan 2024 15:58:02 +0000

The Cuckoo cohort of 2024 takes flight!

Martín Vélez, V., Cano-Povedano, J., Cañuelo-Jurado, B., López-Calderón, C., Céspedes, V., Ros, M., Sánchez, M.I., Shamoun-Baranes, J., Müller, W., Thaxter, C.B., Camphuysen, C.J., Cózar & Green, A.J. Waste Management 10.1016/j.wasman.2024.01.034

General context

Gulls ingest plastic and other litter while foraging in open landfills, because organic matter is mixed with other debris. Therefore, gulls are potential biovectors of plastic pollution into natural habitats, especially when they concentrate in wetlands for roosting.

Novelty

We quantified, for the first time, the flow of plastic and other anthropogenic debris from open landfills to a natural lake via the movement of gulls. We focused on Fuente de Piedra, an inland closed-basin lake in Spain that is internationally important for biodiversity.

Methodology

In 2022, we sampled gull pellets regurgitated in the lake by lesser black-backed gulls Larus fuscus that feed on landfills, as well as their faeces, then characterized and quantified debris particles of ≥0.5 mm. By combining GPS and census data from 2010 to 2022, together with plastic quantification based on FTIR-ATR analysis, we estimated the average annual deposition of plastic and other debris by the wintering gull population into the lake.

Main results

86 % of pellets contained plastics, and 94 % contained other debris such as glass and textiles. Polyethylene (54 %), polypropylene (11.5 %) and polystyrene (11.5 %) were the main plastic polymers. An estimated annual mean of 400 kg of plastics were moved by gulls into the lake. Only 1 % of plastic mass was imported in faeces.

Discussion

Incorporating the biovectoring role of birds can provide a more holistic view of the plastic cycle and waste management. Biovectoring is predictable in sites worldwide where gulls and other waterbirds feed in landfills and roost in wetlands. We discuss bird deterrence and other ways of mitigating debris leakage into aquatic ecosystems.

For UK sites, this work was funded by the Department for Energy Security and Net Zero (DESNZ), through the Offshore Energy Strategic Environmental Assessment research programme, with the contract managed by John Hartley (Hartley Anderson Ltd), and was further funded by Ørsted, and supported by the Marine Renewable Energy and the Environment (MaREE) project (funded by Highlands and Islands Enterprise, the European Regional Development Fund and the Scottish Funding Council).

Declining seabirds on a cliff edge

MIKETOMS — Fri, 22 Dec 2023 08:49:49 +0000

2023-30 21 Dec 2023

Globally important seabird colonies have suffered catastrophic impacts of avian influenza over the last two years. Now, newly published research led by the British Trust for Ornithology (BTO) suggests that the majority of seabird species in Britain and Ireland are also likely to suffer long-term impacts from climate change that may even surpass these recent losses.

The study, published today in the journal Marine Ecology Progress Series, projects that under a scenario of 2°C warming by 2050, some species such as Puffin, Fulmar and Arctic Tern could see population declines of more than 70% compared to their numbers at the turn of the millennium. The results suggest that marine specialist species, including terns, auks and petrels, are at greater risk than more generalist and adaptable species such as gulls. Some species may colonise new areas of Britain and Ireland, but for most species this is not likely to compensate for declines in areas where they currently breed.

The study found that seabirds are generally present in lower numbers where the air temperature is higher during the breeding season, although each seabird species responded in its own way to different aspects of the marine and terrestrial climate. However, it concludes that most seabird species in Britain and Ireland will struggle due to impacts from warming air and sea temperatures, as well as changes in rainfall patterns and other aspects of the marine environment. These changes could potentially reduce food availability for seabirds or increase the likelihood of death due to extreme weather events.

Dr Jacob Davies, BTO Research Ecologist and lead author of the study said: “Here in Britain and Ireland, we are fortunate to host internationally important breeding colonies of seabirds. Our research suggests that many of our much-loved seabird species such as the Kittiwake and Puffin are particularly sensitive to the negative effects of warming and are seriously threatened by climate change.”

“Alongside the potential negative future effects of climate change, many of our seabirds are already in steep decline, due to a range of factors including overfishing and avian influenza. The better we understand the problems these iconic species face and how birds may respond to them, the better placed we will be to help them.”

Dr Rich Howells, Senior Marine Ornithologist, Marine Directorate, Scottish Government, who co-authored the study said: “Climate change is the greatest threat to our internationally important seabird populations. This study provides important information on potential climate change impacts over the long-term, which can be used to inform our conservation actions to increase resilience in seabird populations.”

This paper is available at https://www.int-res.com/prepress/m14462.html

The work was part of the MarPAMM project, funded by the European Union’s INTERREG VA programme and managed by the Special EU Programmes Body.

Marine Directorate is responsible for the integrated management of Scotland's seas. Its purpose is to manage Scotland's seas for prosperity and environmental sustainability, working closely with our key delivery partners and others.

Sharing our gull tracking expertise in a study of Dublin’s ‘noisy neighbours’

WEBSITEEDITOR — Fri, 15 Dec 2023 10:40:29 +0000

PhD student Jon Willans takes us through his fascination with gulls and his fieldwork, which was supported by our scientists. No

Jon Willans PhD student at University College Dublin

Jon has been studying and working with birds for the past 16 years in his native Canada, as well as in Ireland, the USA, Costa Rica, Uzbekistan and the UK.

These are just some of the comments I have heard after people learn that I am a PhD student studying the movement ecology of urban gulls. It turns out that, apparently, not everyone likes gulls or finds them as interesting as I do.

Here in Dublin, like in many coastal cities around Ireland and the UK, there has been a noticeable increase in the number of nesting gulls over the past 30 years. Unfortunately for the gulls, they haven’t been universally welcomed with open arms.

Some human residents feel that the addition of gulls to urban areas should be looked at as a cause for concern and outrage, rather than celebrated as a boost to gull populations — despite drastic declines in gull numbers that have led to some species being listed as of significant conservation concern in Ireland. And human–gull conflict is a growing issue in some cities, where officials are increasingly being pressured into action to control bird numbers by means such as egg oiling, nest removal and even culling.

But, as urban-nesting gulls are a relatively new phenomenon, little is known about how these birds are using these urban environments. Do urban-nesting birds even use the sea? Do they leave the city at all? How does their movement differ from ‘natural’ coastal nesting gulls? Do these coastal-nesting birds generally use the marine habitat for foraging, or do they also spend large amounts of time in the city to find food? The answers to these questions are extremely important when it comes to making any decisions about gull population management.

Urban nesting gulls are a relatively new phenomenon, so little is known about how these birds are using their environment.

An introduction to our research

It was these questions which brought our team, consisting of researchers from University College Dublin (UCD), BirdWatch Ireland, the Irish Midlands Ringing Group and the British Trust for Ornithology, to Ireland at the end of May, to try and shed some light on the movement of locally breeding Herring Gulls.

Specifically, in this study, we wanted to investigate whether there is a difference in the movement ecology — how birds navigate through habitats, and where they go — between birds nesting in urban spaces and on islands around the coast. To determine this, we needed to find both an inland colony and a coastal colony of nesting gulls, and attach GPS units to individual birds. We could then analyse data from birds in the two colony locations to see if or how these birds differ in their use of Dublin’s urban landscape.

Tracking urban gulls ...

university_college_dublin_campus-by-leandro-neumann-ciuffo.jpg

The UCD campus hosts several roof-nesting groups of gulls.

The first stop for the team was the UCD campus in south Dublin — our urban study site — where a small but increasing community of Herring and Lesser Black-backed Gulls can be found nesting on many of the rooftops around the university. While this type of environment is not traditionally associated with ideal habitat for nesting gulls, when you look closer you notice that the campus has everything that the gulls might require.

The tall buildings act as cliffs, where gulls can make their nests with an unobstructed view of their environment, safe from most predators. The many ponds and sports fields on and around the campus provide an ample amount of water and natural feeding opportunities.

A plentiful supply of food is also provided by the thousands of students and staff that make the daily trip onto the campus. On any given day, particularly when the sun is shining, hundreds of people can be found sitting outside eating. Gulls are often fed by these people, but they are also known to snatch food from unsuspecting diners when their hints for a snack are not being met accordingly. The gulls also feast on the mess that is left behind after people have moved on, which sometimes includes pulling rubbish from bins in search of a quick meal. Indeed, some may say this is an urban sanctuary for these birds.

The goal of our team was to catch some of the local birds and attach lightweight GPS units to them, which would give us some information about how these birds are using their environments.

The goal of our team was to catch some of the local birds and attach lightweight GPS units to them, which would give us some information about how these birds are using their urban environments. Over the next two days, working on four different rooftops and spending a considerable amount of time waiting for the unsuspecting birds to walk into the carefully placed, specialist traps, we managed to catch six breeding Herring Gulls.

Once we had taken the birds safely out of the traps, the team went into action. The birds were weighed, and we collected morphometric data like wing, bill and head length. Then we attached uniquely coded rings to their legs and fitted them with their solar-powered GPS units. These units gather and transmit data about the birds’ location and movement speed, which we can use to identify the birds’ behaviours — such as foraging, feeding or resting — as the birds navigate around the landscape.

With six tags deployed and each one actively collecting data, stage one of this mission was complete. We had tagged our urban birds.

... and coastal gulls

jon_williams_by_a._kane_2.png

Jon conducting fieldwork on Dalkey Island, the coastal study site.

Stage two involved moving operations to Dalkey Island, some 10 km to the south-east of UCD as the gull flies.

Although the island is only separated from the mainland by approximately 350 m, after getting off the ferry it felt like stepping into another world. From the herd of Old Irish goats that stopped their grazing to observe us as we arrived on their island, to the sound of the breeding gulls and the buzzing Arctic Terns that nest there, it couldn't have been further removed from the university campus.

Dalkey Island is a more traditional place to find breeding gulls: a rocky coastal area with some scrubby turf and thrift, and plenty of nooks and ledges to make a scrape-like nest. The island has large nesting colonies of Herring, Great Black-backed and Lesser Black-backed Gulls, and when we visited, pairs were scattered all across the island’s east side. Segregated zones marked the presence of the different species: while the massive and intimidating Great Black-backs watched from up high on the grassy slopes, the Herring Gulls were lower down and mainly confined to the rocky areas near the shore and the Lesser Black-backs were scattered at the north end of the colony.

We set more traps and over the next two days, seven more Herring Gulls were caught and selected to collect data for us, fitted with GPS units and sent on their way. Now we had our coastal nesting birds as well. Job done! Well, almost ...

What will we learn about Dublin’s ‘noisy neighbours’?

Early data returns from the GPS units show that there may well be differences in the way these groups of birds behave and use the urban landscape.

Over the next two years, all the GPS tags that the team has worked so hard, and suffered so many bitten fingers, to deploy will be transmitting data back to us and revealing just exactly how the gulls spend their time as they move around this country and perhaps even further afield.

The next step in the research involves analysing all this information. Early data returns from the GPS units show that there may well be differences in the way the urban- and coastal-nesting birds behave and use the urban landscape. As expected, both groups of birds spend a great deal of time inland, visiting the downtown core and the suburbs around the city. However, one initial difference appears to be the birds’ use of the sea: coastal nesting birds make frequent feeding trips out to sea, while the urban nesting birds seldom use this resource and appear to be full-time city dwellers.

Map showing tracks of 13 GPS-tagged Herring Gulls from UCD Campus (yellow square) and Dalkey Island (pink square) between 25–30 May 2023.

Is the sea in ‘seagull’ even applicable to all of these birds? As the data they have unknowingly collected are analysed, all will be revealed — and I for one cannot wait.

The tags deployed over this week of fieldwork will continue to record the movements of these gulls until the specially-designed harnesses break apart and relieve the birds of their GPS units.

What secrets will these data reveal? Is the sea in ‘seagull’ even applicable to all of these birds? These secrets will remain with our gulls for the meantime, but soon, as these birds move around on their daily adventures and the data they have unknowingly collected are analysed, all will be revealed — and I for one cannot wait.

Help us monitor gulls this winter

If you are confident identifying the six main species of gull found in the UK in winter — Herring, Lesser Black-backed, Great Black-backed, Black-headed, Common and Mediterranean — you could join our Winter Gull Survey.

Volunteers will only need to make a small number of visits to gull roosts between 2023 and 2025, but their contributions will help us fill in vital gaps in our understanding of these Amber- and Red-listed species.

How to take part in WinGS

PhD student Jon Willans takes us through his fascination with gulls and his fieldwork, which was supported by our scientists.

1 December 2023

“Why would you want to study seagulls?”
“Those birds are pests — they don’t even belong in cities.”
“They are so noisy!”

15 Dec 2023

Ireland

Behavioural responses of Sandwich terns following the construction of offshore wind farms

VIOLA.ROSS-SMITH — Wed, 06 Dec 2023 14:05:54 +0000

The Cuckoo cohort of 2024 takes flight!

More Details

Thaxter, C.B., Green, R.M.W., Collier, M.P., Taylor, R.C., Middelveld, R.P., Scragg, E.S., Wright, L.J., Cook, A.S.C.P. & Fijn, R.C. Marine Biology 10.1007/s00227-023-04353-7 Offshore wind farms (OWFs) are a key part of efforts to mitigate the impacts of climate change. However, they have the potential to negatively impact seabird species through collisions with turbine blades, displacement from preferred foraging habitat and the perception of wind farms as a barrier to migrating or foraging birds. Whilst the data available to model these impacts are increasing, many data gaps remain, particularly in relation to the impacts of barrier effects. We analyse the movements of Sandwich terns in relation to an offshore wind farm cluster using data collected as part of a multi-year GPS tracking study. Over the course of the study, two additional wind farms were built within the home range of the breeding colony. The construction of these wind farms coincided with a change in the foraging and commuting areas used by breeding terns. Whilst birds entered OWFs when foraging, they appeared to avoid them when commuting, driving an apparent ‘funnelling’ effect to important feeding locations. We discuss if this could be driven by changes to the prey base, subsequent displacement and potentially altered routes reflecting new favourable air flow patterns following OWF construction. Our results suggest that behavioural responses of birds to OWFs may be the result of a complex series of ecological and environmental interactions, as opposed to simplistic assumptions around the perception of the OWF as a barrier to movement. This study was funded by Equinor.

Seabird abundances projected to decline in response to climate change in Britain and Ireland

VIOLA.ROSS-SMITH — Tue, 05 Dec 2023 11:57:57 +0000

The Cuckoo cohort of 2024 takes flight!

More Details

Davies, J.G., Humphreys, E.M., Evans, T., Howells, R., O’Hara-Murray, R. & Pearce-Higgins, J.W. Marine Ecology Progress Series 10.3354/meps14462

Estimating species’ vulnerability to climate change is a key challenge in conservation. Many seabird species are particularly sensitive to negative effects of warming and are thus threatened by climate change. We projected seabird abundance in 2050 in Britain and Ireland, an internationally-important region for seabirds, under climate change scenario RCP8.5. Our projections were based on fitted relationships between abundance and both climatic (air temperature, precipitation) and oceanographic (sea surface temperature, potential energy anomaly) variables, estimated using a Bayesian hurdle model with spatial random effects. The most consistent responses to environmental variables were negative relationships between species presence or abundance and breeding season maximum terrestrial air temperature. Although data and modelling issues meant that future projections could be made for only 15 of the 25 species and with low predictive power for spatial abundance, predictive power was high for spatial presence and moderate for temporal abundance change. Projections suggest that seabirds will generally fare poorly under climate change in Britain & Ireland, with 10 species projected to decline in abundance by 2050. Variable model fit and projection uncertainty limited confidence, which was generally greater for declines than for increases. Fulmar, puffin and Arctic tern were each projected to decline by over 70% with higher confidence. For a few species, colonisation of new areas may reduce projected losses, but this is potentially limited by suitable habitat. Projected abundance change was more negative for marine specialists than for generalists. Our findings highlight the vulnerability and conservation needs of seabirds in a changing climate.

This paper was supported by funding from gifts in Wills to the BTO, for which the authors are extremely grateful. This paper is an output from the Marine Protected Areas Management and Monitoring (MarPAMM) project; the authors thank the project steering group for useful feedback at all stages of the development of the study and Naomi Wilson for the financial administration of the project on behalf of Agri-Food and Biosciences Institute (AFBI). This project has been supported by the EU’s INTERREG VA Programme, managed by the Special EU Programmes Body (SEUPB).

Winter Gull Survey relaunched after 20 years to assess vulnerable gull populations

WEBSITEEDITOR — Mon, 13 Nov 2023 17:09:38 +0000

13 Nov 2023

The Winter Gull Survey (WinGS) was created in 1952 to collect information about the population size and distribution of gulls wintering in the UK, the Channel Islands, and the Isle of Man. Over 70 years later the survey’s overarching objective remains the same but is underpinned by a new urgency: a need to understand and address the various gulls’ recently acquired Red and Amber conservation status.

All the gull species that regularly occur in the UK are listed in Birds of Conservation Concern on the Amber or Red List.

Recent assessments of bird populations in the UK have revealed a decline in both breeding and overwintering populations of gulls. As a result, all gull species that regularly occur in the UK are now listed in the assessment on the Amber or Red List in Birds of Conservation Concern.

The declines are worrying because the UK harbours a significant proportion of the global population of breeding gulls of various species: currently, there are over 50 sites in the UK that have been designated as Special Protection Areas (SPAs) or Special Areas of Conservation (SACs) due to the presence of internationally important numbers of gulls during the breeding season. These sites have enhanced legal protection for wildlife, and are often managed by conservation organisations to help boost populations of vulnerable species.

winter_gull_roost_by_ian_sheppard.png

Winter gull roost, by Ian Sheppard.

Wintering gulls in the UK

The UK is also recognised as an important area for gulls during the winter period. Over the colder months, the gulls’ geographic distribution shifts significantly, and the birds often occupy regions outside of their breeding areas. However, these winter ranges are not considered when designating protected sites, which means that there is little targeted conservation for wintering gulls.

In the upcoming WinGS surveys, we aim to address this gap in protected site designation by monitoring overwintering gulls, collecting key information about their population size and distribution, and providing evidence to underpin the conservation of these species.

How will BTO monitor gulls?

wings-volunteer-at-a-roost-count-by-teresa-frost.jpg

WinGS volunteers will visit key gull roost sites at dusk.

Gulls disperse widely over the landscape during daylight hours, making them a tricky group of species to monitor. Their habit of gathering to roost at dusk provides the best way to make accurate assessments of their numbers. WinGS, which will run during the winters of 2023/24 and 2024/25, is a bespoke survey designed to take advantage of this roosting behaviour.

WinGS volunteers will survey known roost sites at large estuaries and reservoirs – ‘key’ sites – and identify and count the gulls in flight as they arrive in huge numbers around dusk. Some major key sites will necessitate team coordination and create fantastic opportunities for surveyors to connect with fellow gull enthusiasts! WinGS also includes planned visits to ‘random’ sample sites at both inland and coastal locations, which will enable us to generate complete UK-wide population estimates.

The comprehensive WinGS roost counts that we will carry out over the next two years will make a significant step towards addressing the information gaps about gull populations that have arisen in the past two decades.

Both the key and random sites need to be visited at least once in January of 2024 and 2025, and also in the autumn of 2024, when we will assess what are known as ‘post-breeding aggregations’ of birds.

Our focus will be directed towards the six most prevalent gull species in the UK: Black-headed, Common, Herring, Lesser Black-backed, Great Black-backed and Mediterranean Gulls. The Mediterranean Gull was not included as a target species in previous survey seasons of WinGS, but we have decided to include this elegant gull in the scheme in the upcoming surveys due to its increasing reliance on UK sites in the winter months, and the UK’s increasing responsibility for its conservation. This trend was revealed by the BTO/RSPB/JNCC Wetland Bird Survey (WeBS), which saw a sharp increase in the number of these birds recorded at WeBS count sites after 2017.

Charting change

black-headed-gull-by-alan-drewitt-bto.jpg

The Black-headed Gull was the most numerous species during the previous WinGS survey season (2003/04–2005/06), but has declined by as much as 40% since that time.

Long-time BTO survey participants may remember the last WinGS season, which took place during the winters of 2003/04 and 2005/06. At that time, data collected by the survey participants concluded that inland and near-shore coastal waters of the UK supported over 3.8 million wintering gulls.

The most abundant gull species recorded during that survey period was the Black-headed Gull, with an estimated two million birds wintering across the UK. However, more recent population trends based on WeBS data have pointed towards substantial declines of around 40% in this species’ wintering numbers. This trend has no doubt been exacerbated by the effects of Highly Pathogenic Avian Influenza (HPAI), which is thought to have killed around 10% of the total UK breeding population of Black-headed Gulls since March 2023.

WinGS will produce robust evidence and support the development and implementation of effective conservation strategies for the UK’s gulls.

As the previous survey season was so many years ago, we expect to find other changes in the gull populations too. The comprehensive WinGS roost counts that we will carry out over the next two years will make a significant step towards building an up-to-date understanding of how gull populations have altered in the last two decades.

We will combine the information revealed by the WinGS data with that of other key monitoring schemes, including WeBS and the Seabird Monitoring Programme, to produce robust evidence and support the development and implementation of effective conservation strategies for the UK’s gulls.

Learn more about WinGS

Learn about the project’s history and aims, and how to get involved.

Yes

Winter Gull Survey

Waterbird News - Issue 39

NEILCALBRADE — Thu, 02 Nov 2023 12:13:14 +0000

The Cuckoo cohort of 2024 takes flight!

More Details

Flight heights obtained from GPS versus altimeters influence estimates of collision risk with offshore wind turbines in Lesser Black-backed Gulls Larus fuscus

VIOLA.ROSS-SMITH — Tue, 24 Oct 2023 09:34:08 +0000

The Cuckoo cohort of 2024 takes flight!

More Details

Johnston, D.T., Thaxter, C.B., Boersch-Supan, P.H., Davies, J.G., Clewley, G.D., Green, R.M.W., Shamoun-Baranes, J., Cook, A.S.C.P., Burton, N.H.K. & Humphreys, E.M. Movement Ecology 10.1186/s40462-023-00431-z The risk posed by offshore wind farms to seabirds through collisions with turbine blades is greatly influenced by species-specific flight behaviour. Bird-borne telemetry devices may provide improved measurement of aspects of bird behaviour, notably individual and behaviour specific flight heights. However, use of data from devices that use the GPS or barometric altimeters in the gathering of flight height data is nevertheless constrained by a current lack of understanding of the error and calibration of these methods. Uncertainty remains regarding the degree to which errors associated with these methods can affect recorded flight heights, which may in turn have a significant influence on estimates of collision risk produced by Collision Risk Models (CRMs), which incorporate flight height distribution as an input. Using GPS/barometric altimeter tagged Lesser Black-backed Gulls Larus fuscus from two breeding colonies in the UK, we examine comparative flight heights produced by these devices, and their associated errors. We present a novel method of calibrating barometric altimeters using behaviour characterised from GPS data and open-source modelled atmospheric pressure. We examine the magnitude of difference between offshore flight heights produced from GPS and altimeters, comparing these measurements across sampling schedules, colonies, and years. We found flight heights produced from altimeter data to be significantly, although not consistently, higher than those produced from GPS data. This relationship was sustained across differing sampling schedules of five minutes and of 10 s, and between study colonies. We found the magnitude of difference between GPS and altimeter derived flight heights to also vary between individuals, potentially related to the robustness of calibration factors used. Collision estimates for theoretical wind farms were consequently significantly higher when using flight height distributions generated from barometric altimeters. Improving confidence in telemetry-obtained flight height distributions, which may then be applied to CRMs, requires sources of errors in these measurements to be identified. Our study improves knowledge of the calibration processes for flight height measurements based on telemetry data, with the aim of increasing confidence in their use in future assessments of collision risk and reducing the uncertainty over predicted mortality associated with wind farms. This project was funded by the Department for Business, Energy and Industrial Strategy (BEIS)’s Offshore Energy Strategic Environmental Assessment research programme.

Avoidance of offshore wind farms by Sandwich Terns in the North Sea increases with turbine density

VIOLA.ROSS-SMITH — Fri, 20 Oct 2023 09:46:14 +0000

The Cuckoo cohort of 2024 takes flight!

More Details

van Bemmelen, R.A., Leemans, J.J., Collier, M.P., Green, R.M.W., Middelveld, R.P., Thaxter, C.B. & Fijn, R.C. Ornithological Applications 10.1093/ornithapp/duad055 The expanding use of wind farms as a source of renewable energy can impact bird populations due to collisions and other factors. Globally, seabirds are one of the avian taxonomic groups most threatened by anthropogenic disturbance; adequately assessing the potential impact of offshore wind farms (OWFs) is important for developing strategies to avoid or minimize harm to their populations. We estimated avoidance rates of OWFs—the degree to which birds show reduced utilization of OWF areas—by Sandwich Terns (Thalasseus sandvicensis) at 2 breeding colonies in western Europe: Scolt Head (United Kingdom) and De Putten (the Netherlands). The foraging ranges of birds from each colony overlapped with multiple OWFs. We modeled GPS tracking data using integrated step selection functions (iSSFs) to estimate the relative selection of habitats at the scale of time between successive GPS relocations — in our case, 10 min, in which Sandwich Terns traveled ~2 km on average. Besides the effects of OWFs and the direct surroundings of OWFs, iSSFs considered distance from the colony and habitat characteristics (water depth and sediment grain size) as well as movement characteristics. Macro-avoidance rates, where 1 means complete avoidance, were estimated at 0.54 (95% CI: 0.35, 0.7) for birds originating from Scolt Head and 0.41 (95% CI: 0.21, 0.56) for those from De Putten. Estimates for individual OWFs also indicated avoidance but were associated with considerable uncertainty. Our results were inconclusive with regard to the behavioral response to the areas directly surrounding OWFs (within 1.5 km); estimates suggested indifference and avoidance, and were associated with large uncertainty. Avoidance rate of OWFs significantly increased with turbine density, suggesting OWF design may help to reduce the impact of OWFs on Sandwich Terns. The partial avoidance of OWFs by Sandwich Terns implies that the species will experience risks of collision and habitat loss due to OWFs constructed within their foraging ranges. Tracking Sandwich Terns at De Putten was funded by Rijkswaterstaat WVL as part of the Wozep programme. Tracking Sandwich Terns at Scolt Head was funded by Equinor as part of the strategic monitoring programme for Dudgeon.

Arctic Skua migration: stories from the field

WEBSITEEDITOR — Fri, 13 Oct 2023 16:18:50 +0000

Where do Arctic Skuas go when they are not in Scotland? Helen and David Aiton take us through their fieldwork seasons for BTO’s Arctic Skua tracking project, which has followed these fascinating birds across both hemispheres and back. No

Helen and David Aiton

Helen and David Aiton have been members of BTO for over 40 years. Over this period, they have contributed to many BTO surveys and currently have a Breeding Bird Survey site on Rousay.

We were drawn to these beautiful birds by their plaintive calls, their stunning range of plumages and – sadly – their rapid population decline. In 1991, there were 122 pairs in our study area along with thousands of Arctic Terns. Now, in 2023, there are only 17 Arctic Skua pairs and a mere handful of breeding Arctic Terns. This trend reflects that of the UK breeding population more broadly, which is restricted to north and west Scotland and has declined by 70% since 2000.

Our fieldwork site is a triangular area of coastal moorland approximately 2 km by 1.5 km and varies from 5–115 m above sea level. We also research Great Skuas in our study area – but that is a story for another time! The aim of our long-term study is to monitor how both skua species are faring in these turbulent times.

This year, 2023, was the 10th season of our Arctic Skua productivity study, which measures the breeding success of the colony. We collect information about the number of eggs, chicks and fledged young every breeding season. Over the past 10 years, our colony has fledged 96 juvenile birds.

newly_hatched_arctic_skua_chick_still_with_an_egg_tooth.jpg

A newly hatched Arctic Skua chick with its ‘egg tooth’, a sharp point on its beak that helps the chick to break the eggshell from the inside when it is ready to hatch. The egg tooth falls off the beak around a day after hatching.

Fieldwork on Rousay

Each year we visit the study area at least eight times, an effort of 16 days minimum. The island can be reached by a 30-minute ferry trip, crossing the beautiful Eynhallow Sound. Our fieldwork is made more comfortable in our old VW Campervan for overnight stays.

We locate nests at the start of each breeding season from vantage points at least 200 metres away: one person remains at the vantage point and directs the other using radios, to as many as five nests at a time. Arctic Skua nests are well hidden, so we have to use sightlines and surrounding vegetation to memorise their positions, so we can monitor them throughout the season.

Arctic Skua nests are well hidden, so we have to use sightlines and surrounding vegetation to memorise their positions.

We also use our two highly-trained German Shorthaired Pointers to increase the efficiency of finding chicks which have become more mobile and might have wandered away from the nest. It’s very important that we only undertake nest and chick finding in dry, warm weather to avoid the risk of causing any harm due to chilling.

The Arctic Skua tracking project

helen_holding_a_dark-phase_bird_ready_for_release._the_orange_darvic_with_the_geolocator_attached_is_on_the_birds_left_leg.jpg

Helen holding an adult bird ready for release. The geolocator is attached to the uniquely-coded orange ring on the Arctic Skua’s left leg.

Liz Humphreys from BTO Scotland contacted us in 2018, having heard about our well-established study. BTO’s scientists were keen to use geolocators to track the adult Arctic Skuas, to find out where they spent their winters, and to learn more about their migration routes. This information would help inform conservation efforts to protect this species. The work on Rousay would build on the study of Fair Isle breeding Arctic Skuas, which BTO began in 2017, and offer a comparator site. Fair Isle is roughly 30 miles from Orkney.

BTO’s Senior Research Ecologist John Callandine joined us for a week on Rousay, arriving in late May 2018. Luckily for John, we had a week of hot, dry and still weather, almost unknown in Orkney – highly suitable conditions for checking nests and catching adult birds for tagging. He was delighted that we had already located the nesting birds.

Luckily, we had a week of hot, dry and still weather, almost unknown in Orkney – highly suitable conditions for checking nests and catching adult birds for tagging.

john_and_david_with_a_walk-in_trap_over_dummy_eggs_in_the_nest_cup._the_real_eggs_are_safely_stored_in_the_box_john_is_holding.jpg

John (left) and David (right) place a walk-in trap over dummy eggs in the nest cup. The real eggs are safely stored in the box John is holding.

For the tagging project, we chose mostly well-established pairs of adult birds. Over the next few days, we watched the birds and waited for them to lay a full clutch of eggs. We then prepared the walk-in traps – safe structures for catching the adult birds – and left them for a couple of days near the nests, to habituate the birds to them.

Eventually, we placed the traps over the nests, to catch the adults as they walked onto the nest to incubate the eggs. To keep the eggs safe from predators while we tagged the adults, we removed them temporarily and replaced them with dummy eggs before putting the walk-in trap over the nest.

John had honed the techniques for catching birds on Fair Isle the year before, so we were a slick team! We caught 10 individual birds, two of which were a pair. As soon as the tagging was finished we replaced the real eggs. The whole process never took more than an hour.

John then left Rousay to go to Fair Isle to catch more birds, and we continued our study for the rest of the summer. It was reassuring that the birds with geolocators continued to behave normally, with most of them rearing chicks successfully that year.

Collecting the geolocator data

pale_phase_arctic_skua_by_ondrej_prosicky_top_and_dark_phase_arctic_skua_by_maciej_jaroszewski_bottom.png

Arctic Skua plumage falls broadly into two ‘phases’: pale phase (as in the bird in the top photograph) and dark phase (as in the bird in the bottom photograph). Plumage which is intermediate between these phases can also occur in some birds.

Using geolocators as a tool to understand migration routes does not provide instant gratification. To collect the data from the geolocators, they have to be retrieved from the birds, which meant we had to catch the tagged birds again to get any information at all! Innocent of the wiles and intelligence of Arctic Skuas we returned to Rousay in late spring 2019, keenly anticipating retrieving the geolocators and continuing our productivity study.

John joined us again in early June to begin the retrieval process and repeat the procedure using the walk-in traps. However, of the 10 birds we caught in 2018, only eight birds had returned, and one of the birds that did return tried to breed, but her nest failed before we had a chance to try to recapture her with the walk-in traps – down to seven birds.

Arctic Skuas share incubation duties, with both the male and the female sitting on eggs. Because individual Arctic Skuas can occur in one of two plumage types – birds are either ‘dark’ or ‘pale’ phase – we could tell the male and female apart if they had different phase plumage, what we called a ‘dark-pale phase pair combination’. But for a dark-dark phase pair combination, where only one of the pair was carrying a geolocator, we had to take extra care to ensure we were catching the right bird.

The first bird we tried to catch, a female pale-phase bird, walked straight into the walk-in trap and onto the dummy eggs – hurrah – Geolocator Number 1. After this, we thought – this was going to be easy! Alas not. That was the only geolocator retrieved during John’s visit, despite trying for the remaining six birds who all refused to go back into a walk-in trap.

Later in June, we tried mist-netting one pair that had a young chick. A mist net is a fine mesh held taut between two vertical poles, which we can use to safely catch birds by encouraging them to fly or walk into it (in this case, by placing a stuffed predator close by to the net in the hope that the adult birds would fly into the net while mobbing it) but the adults very cleverly called the chick away from the net instead. Sigh!

We were fortunate that one pair – which had had a single egg predated by a neighbouring Arctic Skua (quite common in the skua colonies) – re-laid, and had a young chick less than a week old in late July. With both adults close to their nest, we had the opportunity to try recatching them, and this time both threw themselves into the mist net at the same time! Geolocator Number 2 retrieved.

As in 2018, the colony went on to successfully fledge chicks, including that late chick.

A brief hiatus ...

Due to COVID-19 restrictions in 2020, we were not able to return to Rousay until early July, by which time the chicks were too old for us to try to catch the adults with a mist net. Again, though, it was a good year for the Arctic Skuas and they fledged at least 10 chicks.

... before fieldwork resumed

john_and_david_relaxing_before_johns_ferry_to_mainland_orkney.jpg

John (left) and David (right) relaxing on the Rousay pier after fieldwork was complete.

In 2021, three years after putting the geolocators on the birds, John joined us again in glorious weather in early June. There were still four birds with geolocators breeding in the colony. We successfully mist-netted a female using dummy eggs and a stuffed predator, which she duly mobbed and entered the mist net – Geolocator Number 3 retrieved.

John and David worked very hard to retrieve the remaining three geolocators, but the birds refused to engage with the walk-in traps or the mist nets. Later in June, we tried again with the dark-phase male mate of the first pale-phase bird we retrapped in 2019 – and success! – he eventually walked into the trap and settled on the dummy eggs – Geolocator Number 4. We hoped at the very least that the birds we recaught to retrieve the geolocators this year would give us two years’ worth of migration information.

Finally, after approximately 200 hours of effort, we had four geolocators retrieved, along with six geolocators from John’s work on Fair Isle. The BTO team could set about retrieving the data from the geolocators and plotting the migration routes of the 10 Arctic Skuas. It is no exaggeration that we were all thrilled to see the results.

Migration stories revealed

rousay_skua_wintering_grounds.jpg

Circles show the different wintering locations of individual Arctic Skuas, each of which is represented by a different colour. Two circles of the same colour represent the wintering locations of the same bird in consecutive winters. Different birds from the same breeding colony spent our winter months off the coast of north-west Africa, south-west Africa, or the east coast of South America. The triangle shows the location of Rousay, Orkney, where the Arctic Skuas breed.

The data showed that all the Arctic Skuas travelled south via the North Sea and English Channel. Then down past France, Spain and Portugal to the coast of north-west Africa and on to their wintering grounds.

Individual Arctic Skuas wintered in different locations: off the coast of north-west Africa, the coast of south-west Africa or the east coast of South America. The accuracy of the data is roughly to the nearest 200 km so the birds are not actually on land, as can appear in the maps of the location points – they overwinter at sea. The birds that had data over two winters went back to the same area each year. Astonishingly, our pair of birds that both had geolocators went to different continents!

The work we did in Scotland will also be part of a multi-colony study of Arctic Skua wintering and migration movement involving colonies right across their north-east Atlantic breeding range – some of which was presented by BTO Senior Research Ecologist Nina O’Hanlon to the International Seabird Group Conference in Cork in September 2022 and has now been submitted for peer review. You can read more about the project’s findings in Nina’s blog.

It is rewarding to see the work we contributed to being part of a published international study. Even two years after the maps were produced, it is still deeply satisfying to be able to visualise the journeys of the Arctic Skuas when they are not on Rousay.

Since the Arctic Skua research programme was established in 2017, BTO donors have donated more than £225,000 to fund the work. We are enormously grateful for this very generous support from a small number of committed individuals. The research could not have been delivered without this funding. We would also like to thank the Scottish Ornithologists’ Club for annual grants that cover the cost of the productivity study on Rousay.

World Migratory Bird Day 2023

This blog post was created to celebrate World Migratory Bird Day (WMBD) 2023, a global event which increases the level of awareness about the threats that migratory birds are facing.

The theme of WMBD 2023 is Water, which highlights the importance of this resource for migrating birds – including for species like the Arctic Skua, which spends most of its life at sea and migrates thousands of kilometres over the ocean and across both hemispheres every year.

BTO’s Arctic Skua tracking project aims to understand where these birds spend their time when they’re not at their breeding colonies, so we can better inform global efforts to protect this species.

Discover more about Rousay’s Arctic Skuas and their astonishing migration in our other blog for WMBD 2023, written by BTO Senior Research Ecologist Nina O’Hanlon.

wmbd-2023-poster.jpg

Helen and David Aiton take us through their fieldwork seasons for BTO’s Arctic Skua tracking project.

1 October 2023

Where do Arctic Skuas go when they are not here?

For us, ‘here’ is Rousay, an island which lies off the West Mainland of Orkney. We have been measuring the breeding success of Arctic Skuas since 2014, and working with BTO to help track the adult birds’ migration since 2018.

13 Oct 2023

Scotland