Collaborative projects

Curlew and windfarms 1 – Behavioural responses to offshore windfarms

Lead – Philipp Schwemmer, University of Kiel 
WWRG involvement – Curlew GPS/GSM tagging data.
Outputs – paper published in Journal of Environmental Management

Curlew, a Near Threatened species, are a major feature of The Wash where they occur in nationally important numbers. They are declining throughout their range and in the UK: the 25-year (to winter 2019–20) population trend for Curlew is -33% and the 10 year -18%. In recent years we have equipped some Curlew with GPS/GSM tags which allow us to track their movements in detail. There is much interest in the more-distant movements of Curlew as they leave The Wash and head to their breeding grounds. For Wash Curlew this means crossing the North Sea (and for some the Baltic) heading east on their way to Sweden, Finland, or even Russia.

A Curlew feeding in mud. It has a white leg flag and an orange leg ring.
Flagged Curlew 9P, photo by Cathy Ryden

There are many potential dangers for a bird crossing the North Sea, and the risks have increased as more and more offshore windfarms (OWFs) are being installed as we try to move towards renewable energy sources; however, we know relatively little about the chance of birds colliding with, or being displaced as they avoid, windfarms. To address this, Philip Schwemmer and colleagues brought together data from Curlew tagged in seven countries across Europe consisting of 259 migration tracks for 143 GPS-tagged birds recorded over six years (including data from The Wash birds – 10 tracks in autumn and 10 in spring). The data were used to look at how individuals respond when approaching OWFs in the North and Baltic Seas at two different spatial scales (i.e., within 3.5 km and up to 30 km distance). They found small but significant increases in flight height (particularly within 500 m of an OWF) and changes in horizontal movements as birds tried to avoid turbines. Overall, they estimated that about 16% of Curlew were at increased risk during autumn migration and about 6% at increased risk in the spring (when wind conditions mean their flight heights overlapped with rotor levels far less).

This work has shown how Curlew make small-scale movements to avoid OWFs, which is good as it is likely to reduce collision risk. However, it also shows the substantial barrier effects of OWFs and, given the massive ongoing construction of new OWFs, emphasises the urgent need to quantify the energy costs to birds of avoiding rotors during what must be an arduous flight.

Schwemmer, P., Mercker, M., Haecker, K., Kruckenberg, H., Kämpfer, S., Bocher, P.,  Fort, J., Jiguet, F., Franks, S., Elts, J., Marja, J., Piha, M., Rousseau, P., Pederson, R., Düttmann, H., Fartmann, T. & Garthe, S. (2023) Behavioral responses to offshore windfarms during migration of a declining shorebird species revealed by GPS-telemetry. Journal of Environmental Management 342: 118131.

Curlew and windfarms 2 – Migration flight behaviour of Curlew and Oystercatcher over the North Sea in relation to offshore wind farms

Lead – Chris Thaxter & Sam Franks, BTO
WWRG involvement – Curlew and Oystercatcher GPS/GSM tagging data.
Outputs – paper in peer-reviewed journal

As the development of offshore wind energy continues to expand to meet clean energy targets, it is vital to assess the impact of wind turbines on migratory birds. This project used tagging data from sites across Europe to help understand how the turbines might affect birds and to then use this information to help with future planning. The analysis used data on two Near Threatened species Curlew and Oystercatcher crossing the North Sea and found that both species migrate on a broad front with Curlew being concentrated in the southern North Sea, while Oystercatchers tended to migrate further north. Birds tended to migrate at night, with Curlew at a mean height of 268 m and Oystercatcher 227 m. Ground speeds were similar for both species, but varied with wind, suggesting a potential for significant variation in collision risk with changing wind conditions. This work has identified sensitive areas in the North Sea flyway and both intrinsic and extrinsic effects on collision risk that will (1) help inform where new wind farms will be placed and (2) help in the development of mitigation measures for existing wind farms.

Infection in birds

Lead: Anna Protasio, Cambridge University
WWRG involvement – catching waders for faecal sampling and supplying biometrics for those birds
Outputs – Paper(s) in peer-reviewed journals

This work will analyse faecal samples to detect DNA of any pathogens present. The biometrics of the sampled birds will be used to investigate possible correlations between pathogen load in the gastro-intestinal tract (investigated via DNA sequencing) and markers such as weight, age and so on.

Knot winter movements (PhD project)

Lead: Christine Beardsworth, Liverpool John Moores University, PhD student, Isla Botting, co-supervised by BTO (Sam Franks and Katharine Bowgen) and the Royal Netherlands Institute for Sea Research.
WWRG involvement – supporting fieldwork on The Wash
Outputs – PhD thesis and papers in peer-reviewed journals

The project will investigate the importance of multiple intertidal zones for shorebirds and investigate drivers of movement within and between these areas. It will focus on islandica Knot which moult on the Wadden Sea and then disperse across northern Europe. It will investigate why individuals migrate different distances to a variety of sites, looking at prey availability as well as other environmental and innate drivers (bird ‘personality’ – ‘fast’ and ‘slow’ explorers, which vary in their foraging tactics, dietary choices and movements; Ersoy at al. 2022).  

Birds will be caught and their ‘personalities’ assessed. Their movements will then be tracked by fitting them with small tags which can be detected by receiver stations (ATLAS; Beardsworth et al. 2022) which detect tag transmissions at six-second intervals. Stations will be established on The Wash and in Morecambe Bay and, once birds are detected, they will be located to monitor their feeding behaviour and collect faecal samples for dietary analyses. By improving our knowledge of coastal site connectivity between Dutch and UK coasts, we will be able to predict the resilience of the species to future environmental change. 

Connectivity of wader sites

Lead – Martin Beal – University of Aveiro. 
WWRG involvement – provision of colour-mark resighting and GPS/GSM tagging data for Curlew (ring recoveries have been obtained from the EURING Databank).
Outputs – paper(s) in peer-reviewed journal

As many wader species are declining, the identification and protection of the sites they use throughout their range is crucial to improving their conservation status. This project uses data from ring recoveries, colour-marking and electronic-tracking to quantify site importance based on direct evidence of individual bird movements between sites. Work has already been carried out using Black-tailed Godwit data and has found that combining multiple data sources improved the coverage of the site network used by Black-tailed Godwit throughout the East Atlantic flyway. This work identified sites in Europe and West Africa with high connectivity, some of which are not currently recognised as important to bird conservation. This approach will now be applied to Curlew in the East Atlantic Flyway and the analysis will include WWRG ring-recoveries, colour-mark resightings and GPS/GSM tagging data. The explicit consideration of site connectivity can help improve the ecological representativeness of protected area networks for migratory waterbirds and their wetland habitats.

Curlew survival

Lead – Aonghais Cook, BTO
WWRG involvement – provision of colour-mark resighting and ring recovery data, author and comments  on paper.
Output – paper published in Biological Conservation

Curlew is a declining Near Threatened species that winters on The Wash and also uses it as a passage site. To understand why Curlews are declining, we need to look at the whole life cycle and consider birds from different parts of the country. Aonghais Cook and his colleagues (which included several WWRG members) used information on ringed birds to understand not only how survival rates have changed over time, but also whether they differ in different parts of the country. The analysis used data from WWRG and from ringing groups studying Curlew on the Severn, Tees and Moray estuaries, and in North Wales to estimate survival using data from birds that were found dead with resightings of colour-marked birds. This maximises the amount of information available, but it does require careful analysis as the probability that a dead bird is found and reported is quite different from the probability that a colour-marked bird is seen. Differences in probability of being seen also need to be considered to get robust estimates of survival.

Cook and colleagues found a number of interesting results. Firstly, survival of adults was generally high (>90%) which might be expected of such a large, long-lived bird. They also found that, if anything, survival had increased over time, especially on The Wash and the Severn estuary – in part because Curlews were afforded protection from hunting in 1982. In addition, they found that survival was reduced during cold winters and when there was a high density of Curlew, such as might happen if individuals are crowded into smaller areas through habitat loss. It seems that the decline of Curlews is not due to increased levels of mortality reducing survival.

Next, Cook and colleagues used information on productivity (the number of chicks that a pair of Curlew can raise) and found that, on average, each nest fledged 0.25 chicks (i.e. one chick fledges for every four Curlew nesting attempts). A healthy population would require a productivity of 0.4–0.5 chicks per nest (i.e. nearer to one chick for every two nests). Thus, the decline of the Curlew appears to be driven by factors operating on the breeding grounds, which fits with what we know about the high predation rates that ground-nesting birds can suffer in some areas.  

Cook, A.S.C.P., Burton, N.H.K., Dodd, S.G., Foster, S., Pell, R.J., Ward, R.M., Wright, L.J. & Robinson, R.A. (2021) Temperature and density influence survival in a rapidly declining migratory shorebird. Biological Conservation 260, 109198.

Prehistoric population sizes of waders

Lead: Bill Amos & Rhys Green, University of Cambridge
WWRG involvement: Collecting samples of buccal cells using swabs
Outputs – paper(s) in peer-reviewed journal

This project aims to estimate the population history of bird populations from DNA collected using buccal swabs to collect cells from inside the mouth. In the UK, we are very fortunate to have long-term data for many of our bird species, though even these only reach back a few decades. Recent developments in DNA sequencing and analysis of genetic variation between individuals has enabled estimation of how populations have changed over tens of thousands of years. Genetic data can be used to build trees, rather like family trees, with the rate of branching being an indicator of success. Using this principle and complicated mathematics, it is possible to gain an idea of how big the population size is now relative to past populations.  

The Cambridge University team plan to calculate average population histories for groups of birds from major habitat types, including wetlands. This will provide a better understanding of the links between bird populations and significant prehistoric habitat change. For example, it is hoped that we will discover more about what may have happened to Curlew in the period between the end of the last glaciation and conversion of land for farming and grazing in the last few thousand years.  

Oystercatcher tracking in relation to shellfish stocks

Lead: Gary Clewley, BTO
WWRG involvement: Catching Oystercatchers and equipping them with tags
Outputs – BTO Research Report

The winter population of Oystercatcher on The Wash is ca. 20,000 individuals and has been shown previously to be sensitive to declines in shellfish abundance. Consequently modelling approaches are used to set sustainable limits of shellfish ‘take’ (the amount harvested by fishermen) to ensure both conservation and commercial interests are balanced. These models require parametrisation using data collected on the waders within The Wash. We equipped 10 Oystercatchers with solar powered GPS/GSM devices using leg-loop harnesses to investigate their daily movements around The Wash during the 2020/21 winter. 

Seven birds remained on the eastern shore but apparently moved freely up and down the coast. Two individuals made repeat visits between the east and west shores of The Wash over the winter but spent the majority of time near the catch site. One individual left the site entirely for about a month, moving up to the Humber Estuary before returning to The Wash. The mean (± S.E.) maximum distance recorded away from the previous high tide roost location during the following low tide was 5.8 ± 0.14 km. Our findings confirm that while patch switching does occur, and even visits outside of the estuary system entirely, this was a minority strategy for the sample of birds tracked in this study and individuals mostly remained close to the roost location where they were originally caught. However, it is expected that individuals caught at different sites and from different age classes may behave differently. 

Clewley, G.D., Franks, S.E., Clark, N.A. & Robinson, R.A. (2021). Pilot study to investigate Oystercatcher (Haematopus ostralegus) feeding behaviour to enhance bird food modelling and shellfisheries management on The Wash. BTO Research Report 735, BTO, Thetford, UK.