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.

The Wild Bird Indicators are part of the government’s suite of biodiversity indicators, alongside indicators related to measures of habitat condition, air pollution, river water quality, extent of protected areas, spread of non-native species as well as the state of butterflies and other wildlife. The indicators are produced annually for Defra and NatureScot by BTO, together with RSPB and JNCC. The Wild Bird Indicator is an accredited Government Official Statistic, and further information on its construction and how it is developed can be found on the government website. The Wild Bird Indicators are based on population trends of bird species that are native to, and breed or spend the winter in, the UK. These population trends are calculated largely using data that is collected by volunteers, as part of national bird monitoring schemes like the BTO/RSPB/JNCC Wetland Bird Survey and the BTO/JNCC/RSPB Breeding Bird Survey. The indicators therefore link the efforts of our dedicated volunteers directly to a policy-relevant assessment of the state of nature. The indicators group breeding birds by habitat: farmland, woodland, uplands, waterways and wetlands, and marine and coastal areas, and most are based on datasets that stretch as far back as 1970. This means that indicators are a useful tool for examining how birds associated with different landscapes have fared over many decades. The indicators also report on the state of our internationally important wintering (i.e. non-breeding) wetland and coastal birds.

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.