Bailiwick Bat Survey: 2023 season report

The Bailiwick Bat Survey capitalises on the interest and enthusiasm of volunteers to participate in biodiversity monitoring to systematically collect bat distribution and activity data across Guernsey, Alderney, Herm and Sark through a project that will run over four years. This will result in the production of a robust dataset, which will increase knowledge and understanding of bat distribution and activity across the Bailiwick of Guernsey. Based around 500 x 500-m squares, this project will provide a detailed description of the islands’ bat fauna.

Whilst the focus of this work is bats, results for small terrestrial mammals, bush-crickets and audible moths which are recorded as ‘by-catch’ during bat surveys are also returned. Working with a network of volunteer fieldworkers, static acoustic bat detectors were deployed over an eight month survey season to provide a third year of baseline data for bats for Guernsey, Alderney, Herm and Sark. This report provides an overview of the survey coverage and main results from 2023.

During 2023, 582 different locations across the Bailiwick of Guernsey were surveyed. Recording was undertaken on 228 different nights mainly between April and the end of October, amounting to a total of 2,260 nights of recording effort across sites. Sound recordings (wav files) were uploaded by fieldworkers to the BTO Acoustic Pipeline, where a first automated analysis was carried out and provisional results returned. Recordings were then moved to deep glacial storage for later auditing. At the end of the survey season, a copy of the recordings was pulled back, and manual auditing of the results / recordings carried out.

Overall, 3,825,977 five second triggered recordings were collected which, following analyses and validation, were found to include 994,021 bat identifications, and 7,973 small terrestrial mammal identifications. There were also over two million identifications of bush-crickets as ‘by-catch’, for which we report species presence on a site and night basis. Following validation, the study confirmed the presence of at least 13 bat species, five small mammal species, and six species of bush-crickets. Through the project, we have a better understanding now of the status of bats across the islands. The report includes a full species-by-species breakdown of spatial, seasonal, and through-the-night patterns of activity.