Understanding the habitat requirements of Short-eared Owls can inform conservation action for this species. Given the vast distances that individual Short-eared Owls can travel over the course of a season, we need to understand how these requirements may vary between locations. A substantial proportion of Britain’s Short-eared Owl population breeds on managed moorland, where these avian predators specialise on small mammal prey. Such moorland is widely managed for Red Grouse through the control of predators and the burning of vegetation, practices which can be controversial. Efforts to increase or restore heather and other dwarf-shrub cover, which are seen by many as a conservation priority, may also alter the nature of the moorland habitat used by Short-eared Owls. Set against this background, it has become especially pertinent to understand how Short-eared Owls use moorland habitats and, in particular, the different vegetation types present. Because of their nomadic behaviour, there is also a need to understand how these birds use similar open habitats elsewhere. This tracking study, which involved 17 fully-grown Short-eared Owls tagged with GPS tracking devices in Scotland between 2017 and 2020, provided an opportunity to look at individual habitat use across the different sites used by these birds in Scotland, England and Norway. The study looked at habitat use within individual home ranges, i.e. those areas used by the birds for more than five consecutive days and which were less than 500 hectares in size. Locations within 50 m of nest sites were excluded from the analysis because females may continuously incubate eggs or brood small chicks, skewing attempts to understand habitat use. Relative to their availability, there was a tendency for Short-eared Owls in Britain to preferentially use areas of grassland, including those smaller patches located within a wider Heather-grassland mosaic. In contrast, the tracking data from those individuals that also spent time in Norway revealed a tendency to hunt more over dwarf shrubs. The dwarf shrub community in Norway is more diverse than here in Britain, both in terms of species composition and structure. Such differences are likely to reflect prey availability, but they also highlight the behavioural plasticity of these birds. The results of this work can be used to inform relevant conservation strategies in at least three different ways. They inform the habitat management of specific sites, highlight landscapes towards which targeted management could be directed, and identify specific sites for conservation designation, protection and management.

Accumulation of plastic and waste contamination in the natural environment is a growing problem, but little is known of the role animals play in transporting plastics (a process known as ‘biovectoring’) particularly to inland waters and habitats. This study used diet sampling, population monitoring and GPS tracking data of Lesser Black-backed Gulls to monitor the transport of plastics and anthropogenic debris from landfills to an inland reservoir in Spain. The study, led by the Institut de Ciències del Mar and Estación Biológica de Doñana, CSIC, Spain, used diet samples collected in January 2022 at the Fuente de Piedra – an inland lake in Spain that is internationally important for biodiversity. Monthly counts of Lesser Black-backed Gulls were carried out to assess the numbers of birds present at the lake. GPS tracking data collected from studies across Northern Europe, including some led by BTO, were used over 12 ‘winters’, between January to March 2010–22, to understand the spatial movements of individual birds in the local region, coinciding with when birds are either on wintering grounds or on migration. The authors found that a high proportion (94%) of material regurgitated by gulls contained human-related material such as glass and textiles and 86% contained plastics, whereas only 1% plastic mass was present in faeces. Numbers of Lesser Black-backed Gulls at the lake were highest in January, peaking at a maximum count of 33,000 in January 2020. Agricultural habitats were most frequently used by gulls (88% time) as well as three landfill sites in the local area, with some landfills visited more than others, linked to use of bird deterrence measures. A total of 77% of the tracked birds visited at least one of the three landfills on a given day. The authors estimated that, on average, the annual deposition of plastic and other debris by the wintering gull population into the lake was 1,888 g per day, meaning that 400 kg of plastic were estimated to be deposited into the lake each winter, though only ca. 5 kg were from faeces. This study sheds new light on the importance of gulls for biovectoring within ecosystems, and the leakage of plastic and debris from landfills into inland waters. The plastics can accumulate in sediments and become incorporated into food webs, presenting a global contamination issue that needs addressing. The study further highlights the importance of adopting initiatives to tackle the problem, such as waste separation and plastic reduction measures, and bird-deterrence to reduce ingestion by birds at source.

BTO-led research highlights the importance of the quality of protected areas in their effectiveness.

Satellite-tracked male Cuckoos show higher fidelity to sites used during the breeding season than to sites used at other times of the year.

Tracking the long-distance migrations of Arctic Skuas from their north-east Atlantic breeding grounds revealed complex migration strategies, with mixing of individuals from different populations at important staging areas before the birds reached their southern wintering grounds. Arctic Skuas are long-distance migrant seabirds that have seen large declines in breeding numbers across areas of the north-east Atlantic. Part of these declines has been attributed to poor food availability during the breeding season, exacerbated by predation from Great Skuas, particularly in years where food availability is low. However, Arctic Skuas only spend around a third of the year at their breeding grounds. Therefore, they likely also face a range of threats during the non-breeding season. To shed light on the migration routes and strategies of Arctic Skuas, researchers, including BTO scientists, tracked 131 individuals with small tracking devices called geolocators between 2009 and 2019, collecting information from four breeding populations: Scotland, the Faroe Islands, Norway and Svalbard. This collaboration revealed extensive mixing of Arctic Skuas from different breeding populations during migration in several discrete staging areas. An area of high marine productivity, part of which has recently been designated as a high seas Marine Protected Area, was particularly important to the skuas during both their south-bound (autumn) and north-bound (spring) migrations. Because of their predictable food sources, such staging areas are vital, fuelling long flights to the wintering areas and, during spring, enabling individuals to build up reserves for the upcoming breeding season. This considerable mixing of individuals means that if adverse conditions affect the skuas in these important staging areas, then it has the potential to negatively impact multiple breeding populations through reduced survival or productivity. However, the data also revealed some differences in the migration routes and staging areas of individuals from the different breeding populations. Specifically, during southbound migration, skuas from Scotland largely migrated south through the North Sea and along the Iberian Peninsula, whilst those from the other more northerly populations tended to head west towards the mid-Atlantic staging area. Individuals from Svalbard staged much further west in the Atlantic during both migrations, where they may have encountered different, potentially more favourable, conditions given that the Svalbard population appears to be declining less severely than other populations in the north-east Atlantic. Understanding where long-distance migrants, such as Arctic Skuas, are distributed during migration and the strategies they use is a vital first step in identifying threats that individuals may encounter en route, and how this may affect their survival, productivity and therefore population trends. This new knowledge will help us prioritise future research and conservation actions for this declining charismatic seabird. View the Press release associated with this publication