BTO - British Trust for Ornithology - Tracking

Cuckoo Tracking Project

WILLIAMSKELLORN — Thu, 25 Oct 2018 10:17:22 +0000

The Cuckoo Tracking Project has been revealing new discoveries about how British Cuckoos migrate, and the challenges they face. Follow and support this ground-breaking project.

Friday, April 1, 2011 - 00:00

Help us follow Cuckoos on migration and discover why they are in decline

We’ve been satellite-tracking Cuckoos since 2011 to find out why they are in decline:

Since 1995, the number of Cuckoos has decreased by over 30%.
The Cuckoo is currently Red-listed as a Bird of Conservation Concern in the UK.
Support this project by sponsoring a Cuckoo >

Progress so far

We’ve learned lots of vital information, such as how the different migration routes are linked to declines, and some of the pressures Cuckoos face whilst on migration, but there is still much more to discover.

We have been able to share our expertise around tracking Cuckoos with other international studies, such as the Beijing Cuckoo Project.
Read more about our Cuckoo Tracking Project.

What’s next

We now need to look more closely at how dependent Cuckoos are on, and how much their migration is linked to, the drought-busting rains of the weather frontal system known as the Inter Tropical Convergence Zone (ITCZ) as they move out of the Congo rainforest and begin to head back to the UK via West Africa.

Our Cuckoo Tracking Project is vital and it wouldn’t be possible without the amazing support from funders and sponsors.

Sponsor a Cuckoo

Watch the Cuckoos migrate on our map

Each Cuckoo’s tag sends us location data approximately every day, so we can follow them and learn more about their migration.

Track our Cuckoos as they migrate

Chris Hewson

5/11 - First round of five Cuckoos tagged, wintering sites in the Congo identified
3/12 - Different routes discovered on return journeys
2016 - First scientific paper published on on the routes of our Cuckoos

Spend as much time as you like following each Cuckoo's migration on the map below - use the controls to animate or step through their movements. No technical skills are required to support this project - just a love of Cuckoos.

Cuckoo declines linked to different migration routes to Africa

ongoing Farmland birdsWoodland birds funding Yes cuckoos@bto.org

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!

More Details

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).

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 ...

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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

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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.

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.

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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

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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.

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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

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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

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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

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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.

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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

Combining remote sensing and tracking data to quantify species’ cumulative exposure to anthropogenic change

VIOLA.ROSS-SMITH — Tue, 10 Oct 2023 09:15:21 +0000

The Cuckoo cohort of 2024 takes flight!

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Buchan, C., Gilroy, J.J., Catry, I., Hewson, C.M., Atkinson, P.W. & Franco, A.M.A Global Change Biology 10.1111/gcb.16974 Identifying when and where organisms are exposed to anthropogenic change is crucial for diagnosing the drivers of biodiversity declines and implementing effective conservation measures. Accurately measuring individual-scale exposure to anthropogenic impacts across the annual cycle as they move across continents requires an approach that is both spatially and temporally explicit—now achievable through recent parallel advances in remote-sensing and individual tracking technologies. We combined 10 years of tracking data for a long-distance migrant, (common cuckoo, Cuculus canorus), with multi-dimensional remote-sensed spatial datasets encompassing thirteen relevant anthropogenic impacts (including infrastructure, hunting, habitat change, and climate change), to quantify mean hourly and total accumulated exposure of tracked individuals to anthropogenic change across each stage of the annual cycle. Although mean hourly exposure to anthropogenic change was greatest in the breeding stage, accumulated exposure to changes associated with direct mortality risks (e.g., built infrastructure) and with climate were greatest during the wintering stage, which comprised 63% of the annual cycle on average for tracked individuals. Exposure to anthropogenic change varied considerably within and between migratory flyways, but there were no clear between-flyway differences in overall exposure during migration stages. However, more easterly autumn migratory routes were significantly associated with lower subsequent exposure to anthropogenic impacts in the winter stage. Cumulative change exposure was not significantly associated with recent local-scale population trends in the breeding range, possibly because cuckoos from shared breeding areas may follow divergent migration routes and therefore encounter very different risk landscapes. Our study highlights the potential for the integration of tracking data and high-resolution remote sensing to generate valuable and detailed new insights into the impacts of environmental change on wild species. The BTO Cuckoo Tracking Project was funded by the A. G. Leventis Foundation, BBC Wildlife Fund, Dulverton Trust, BTO including from much appreciated gifts in Wills, Ernest Kleinwort Charitable Trust, Essex and Suffolk Water, Mark Constantine, Tobit Trust and ‘Cuckoo Sponsors and Champions’. The authors thank everyone who provided assistance in the field, Paul and Russell Howey for assistance with PTTs, and BTO Fundraising and Communications teams for vital contributions to the project. CB was funded by a PhD studentship from the Natural Environment Research Council, grant number NE/L002582/1. IC was funded by contract 2021.03224.CEECIND from FCT (Fundação para a Ciência e Tecnologia).

LifeCycle issue 12, Summer 2023

LEECARNIHAN — Wed, 13 Sep 2023 10:13:10 +0000

The Cuckoo cohort of 2024 takes flight!

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A crowded ocean: the need for demographic and movement data in seabird conservation

VIOLA.ROSS-SMITH — Fri, 01 Sep 2023 13:45:30 +0000

The Cuckoo cohort of 2024 takes flight!

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O’Hanlon, N.J., Johnston, D.T., Cook, A.S.C.P., Robinson, R.A. & Humphreys, E.M. Ocean and Coastal Management 10.1016/j.ocecoaman.2023.106833

Species face a multitude of stressors due to human activities, especially in marine environments. Seabirds are among the most threatened group of birds globally. A key challenge in their conservation is quantifying the impact of multiple interacting stressors on populations effectively, especially for species that undertake large-scale movements.

We use the relatively well-studied Black-legged Kittiwake Rissa tridactyla as a case study to highlight knowledge gaps in demographic rates and how key stressors act on populations across different parts of their biogeographic range. From this starting point we provide a strategic approach to identify and prioritise data collection and research efforts from species and regions where data are currently lacking.

Obtaining accurate and precise empirical data on demographic rates and movement will increase the predictive accuracy, and realism, of population models, and confidence in how populations will respond to multiple stressors over the life and annual cycle, facilitating better management decisions.

BTO - British Trust for Ornithology - Tracking

Cuckoo Tracking Project

Help us follow Cuckoos on migration and discover why they are in decline

Progress so far

​What’s next

Support the project

Watch the Cuckoos migrate on our map

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

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

An introduction to our research

Tracking urban gulls ...

... and coastal gulls

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

Help us monitor gulls this winter

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

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

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

Arctic Skua migration: stories from the field

Fieldwork on Rousay

The Arctic Skua tracking project

Collecting the geolocator data

A brief hiatus ...

... before fieldwork resumed

Migration stories revealed

World Migratory Bird Day 2023

Combining remote sensing and tracking data to quantify species’ cumulative exposure to anthropogenic change

LifeCycle issue 12, Summer 2023

A crowded ocean: the need for demographic and movement data in seabird conservation

What’s next