This study uses Hen Harrier records from the Hen Harrier Winter Roost Survey and BirdTrack to explore the distribution of wintering Hen Harriers in relation to the distribution of Special Protection Areas (SPAs). There is a particular need to enhance survey effort in and around SPAs, to improve our understanding of the distribution and habitat use of non-breeding Hen Harriers in England, and to evaluate whether there is a need for site protection to be extended to more areas.

This report, which is an addendum to BTO Research Report 766, examines the potential impacts of current and proposed wind farm developments on the Red Kite population in Wales

This BTO Research Report explores the ability of data collected through the Bailiwick Bat Survey to produce robust long-term monitoring trends for a suite of species.

Thanks to our members, funders and supporters, £7.3 million was spent during the year carrying out, supporting and communicating our ornithological research and delivering engagement. Through our Bird Study journal, we brought together 22 important scientific papers that shed new light on the avian influenza outbreak and help direct our response to this devastating disease. Our Together Through Nature (Thetford) project has given us the foundations needed for a successful community project, working with people who don’t usually have the opportunity to engage with nature and BTO. Some 43,679 BTO volunteers have contributed to Garden BirdWatch, which has celebrated 30 years of recording this year, generating 10.6 million weekly observations. Volunteers contributed 2,643,682 hours to BTO work during the year, mainly through our bird surveys and monitoring schemes. This incredible effort has an estimated financial value of more than £54 million. During 2024/25, we received just under £800,000 through gifts in Wills, something for which we are phenomenally grateful.

This report investigates the accuracy and reliability of seabird flight height data that are used to mitigate impacts of offshore wind farms on seabird populations. Through a set of trials, we set out to validate Light Detection and Ranging (LiDAR)-coupled Digital Aerial Surveys (DAS), and to a lesser extent size-based methods. Additional technologies evaluated in the trials included bird-borne Global Positioning System (GPS) telemetry tags and human-operated laser rangefinders. We found that the comparative performance of the two LiDAR-coupled Digital Aerial Survey suppliers varied based on system differences and weather conditions during surveys, particularly in terms of detection rates from different sensors. LiDAR flight height measurements, however, proved to be accurate and precise for both suppliers, with measurement uncertainties on the scale of centimetres. In contrast, size-based DAS estimates had uncertainties on the order of tens of metres. Findings from this study will directly inform the development of best practice guidance for seabird flight height data collection and analysis, supporting impact assessments for offshore wind farms while minimising ecological risks to seabird populations.

Sporting and leisure activities are common at the Northern Irish sea loughs. Human-related disturbances to foraging or resting waterbirds can come from a range of sources, from people on foot or using machines or vehicles, and from industrial or recreational activities. Such disturbances may cause birds to fly away to alternate areas or cause non-fleeing responses like increased vigilance. This pilot project builds on the findings of an analysis of within-site wintering waterbird trends, and provides a more targeted field-based study that directly assesses the potential responses of waterbirds to disturbance. A particular focus of the work is disturbance associated with intertidal aquaculture activities at sites across Northern Ireland, and the report seeks to set these in the context of disturbance events caused by other activities.

This report presents results from the first year of passive acoustic monitoring as part of the pilot of the Rewilding Monitoring Framework, working with Radnorshire Wildlife Trust. These data will contribute to baselining and monitoring rewilding progress and its impact on biodiversity.