Occupancy and density of the badger (Meles meles) in Britain

Mammals include species of ecological, economic and cultural importance. In Britain, the badger is a particularly unusual case, because it is both protected, as the subject of specific legislation (the Protection of Badgers Act 1992), and persecuted, in a contentious approach to controlling the transmission and incidence of bovine tuberculosis (Fig. 1).

Despite the high level of public interest arising from these apparently contradictory factors, the abundance and distribution of badgers - like those of the majority of terrestrial British mammals - have not been intensively monitored at a national scale. Most of what is known about the dynamics of the national badger population comes from three major national sett surveys conducted over the past four decades.

Although these represent vast coordinated efforts, their low frequency and indirect nature (i.e., surveying setts, rather than badgers) make them a blunt tool for assessing the factors that drive the abundance and distribution of badgers. For that to be successful, sustained and widespread monitoring would be required. In 2023, the Badger Trust launched its State of the Badger Project to produce a comprehensive report on the status of the UK badger population, threats, and recovery.

To assess population abundance, the Badger Trust is exploring ways of applying a citizen science approach to data collection.

Recently, the People's Trust for Endangered Species launched a pilot of a National Hedgehog Monitoring Programme (NHMP). The NHMP recruits groups and organisations concerned about the fate of the hedgehog. Each contributing group agrees to adopt one or more sites of c. 1km2, and to survey that site annually for 30 days.

Surveys involve the deployment of 30 camera traps on a systematic grid. Camera placements are distance-calibrated using a standard method [1] (Fig. 2), so that the captured images can be used for density estimation [2,3].

Given the protocol used for the NHMP, there is no reason why the data collected cannot also be analysed to provide information on the occupancy, density and ecology, more generally, of the badger. Furthermore, the methodology complements existing and proposed approaches to badger monitoring, such as sett surveys to measure social group abundance [4] and social group size counts.

Given the shared interests in citizen science and wildlife monitoring there is enormous, unlocked potential in integrating the efforts of the range of groups recruited to the NHMP with the badger interest groups in the programme to produce mutual benefits for both hedgehog and badger enthusiasts. This project will focus on working with the Badger Trust to recruit badger groups to develop and assess their survey protocols and increase the spatial coverage of the surveys. Thus, the aims of this project are:

(1) to extend and increase spatial coverage of the NHMP through the recruitment and training of badger groups, to enable them to conduct surveys;

(2) to extract badger data from across the NHMP surveys, conducting analyses of occupancy, density and activity in relation to local environmental characteristics;

(3) to assess the robustness of inferences derived from simultaneous sett surveys, together with extrapolations from estimated group sizes [4]; and

(4) to assess the value of ad hoc sighting data (e.g., from iRecord and iNaturalist) for inferring occupancy and relative densities of badgers, alone and in combination with camera trap data.