DEN SITE CAN DETERMINE SHAPE AND SIZE OF BADGER TERRITORIES - IMPLICATIONS FOR GROUP-LIVING

Much discussion of the determinants of carnivore sociality has been dogged by its reliance on largely untestable hypotheses. Here we employ spatial analysis of published data on badger (Meles meles) setts and latrine sites from five study localities in Britain to test the idea that den locations can determine territory shape and size. Territorial boundary points were identified from latrines shared between two or more main setts. These were found to lie in close proximity to the hypothetical borders of a fixed-territory model constructed from Dirichlet tessellations around main setts. At three localities the fit was better than chance expectation, given by points scattered at random and repelled from main setts. These results suggest a functional interpretation of territorial behaviour, in terms of maximizing reproductive success by defending an established breeding den, which the conventional models of central-place foraging do not encompass. A test of the Dirichlet borders against a model of differential expansion suggested that occupants of some main setts could expand one or more borders to the detriment of neighbouring territories, probably in response to variations in food availability around the given den sites. The implications of these results are that (1) by defining territory size, suitable den sites for breeding and overwintering may impose an upper limit on the density of badger social units, and (2) the distribution of main setts may therefore influence the size of group that can be accommodated in the resulting territory. The question of why badgers are sociable therefore finds a reply with unexpected significance given to the location of dens. We suggest the model might be appropriate to other vertebrates for which an established den or nest site could represent a key resource to be costed in an energy currency in the animal's defence budget.