Increasing frequency of bite wounds with increasing population density in Eurasian badgers, Meles meles D. W. MACDONALD, B. J. HARMSEN, P. J. JOHNSON & C. NEWMAN Wildlife Conservation Research Unit, Department of Zoology, University of Oxford (Received 9 March 2003; initial acceptance 28 April 2003; final acceptance 30 August 2003; MS. number: 7644) Eurasian badgers sometimes live in territorial, mixed-sex groups; the adaptive significance of this is not understood, but members generally interact amicably. None the less, badgers occasionally fight and inflict sometimes severe wounds on one another. Based on 498 badger life histories, from first emergence as a cub until death, documented during a 10-year trapping study at Wytham Woods, Oxfordshire, U.K., the patterns and rates of bite wounding and consequential scarring were examined. Male badgers received more wounds and more severe wounds than did females. Wounding rates for both sexes increased significantly with age, and there was evidence that heavier individuals received most wounds. No seasonal pattern in wounding rates was apparent. During the study, the badger population size increased three-fold and wounding rates, particularly in males, showed a density-dependent increase. The rate of bite wounding increased with group size, and this increase was more marked among males than among females. Among males, but not females, the rate of bite wounding also increased with the number of badgers living in adjoining territories. Ó 2004 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. Despite prolonged study, the social system of Eurasian badgers has so far eluded more than superficial un- derstanding (Kruuk 1989; Woodroffe & Macdonald 1992; da Silva et al. 1994; Neal & Cheeseman 1996; Macdonald et al. 2002a). Evidence is emerging that ectoparasite control is one fundamental form of cooperation in badger society (Stewart & Macdonald 2003; Johnson et al., in press) whereas evidence of alloparental behaviour remains preliminary (Woodroffe 1993). There is, however, no evidence of a stable social hierarchy within badger groups (Macdonald et al. 2002a), but a conspicuous feature of badger society is that individuals fight both within and between groups, as revealed by video observations of our study population (Stewart et al. 1997b). Fighting most often involves ritualized escalations of aggressive behaviour, starting with jaw-to-jaw contests, which can proceed to mutual neck biting, which, although dangerous, provides neither badger with a clear advantage. Severe fighting involves badgers trying to avoid exposing their heads to attack, so strikes are directed against the opponent’s body. An advantage in such a contest is achieved if one combatant locks a bite on to the opponent’s rump and circles swiftly to prevent the manoeuvre being reciprocated. The bitten individual will ultimately pull away and savage, extensive rump wounds can be inflicted in this way on the skin and subcutaneous tissue of the recipient. Later examination of fresh wounds often reveals secondary infection, the presence of maggots and necrotic tissue, so there are additional chronic health implications to severe wounding. Successful healing of a wound produces inelastic granular tissue, often nodular, which might provide considerable protection against future bites (Keeble 1999). Badgers have an unresolved role in the transmission of bovine tuberculosis (bTB; Krebs et al. 1997). Mycobacterium bovis, the bacterium responsi- ble for bTB, has been isolated from the swabbed wounds of infected badgers and thus bite wounding may be an important factor in the spread of bTB within badger populations (Gallagher & Nelson 1979; Clifton-Hadley et al. 1993). The contexts of these fights are not yet understood, but their consequences are clearly visible, and quantifiable in the form of variously severe wounds or subsequently scars. We have live-trapped, and examined closely, a substantial proportion of our study population at Wytham Woods, typically four times annually since 1987 (Macdonald & Newman 2002), and have recorded the incidence of these injuries. Thus, we have the opportunity to evaluate how frequently badgers incur injuries from bites, and how this incidence varies with their sex, age and weight. Further- more, during our study, the population size and group sizes have increased and changed in spatial organization, Correspondence: D. W. Macdonald, Wildlife Conservation Research Unit, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, U.K. (email: david.macdonald@zoology.ox.ac.uk). 745 0003e3472/03/$30.00/0 Ó 2004 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. ANIMAL BEHAVIOUR, 2004, 67, 745e751 doi:10.1016/j.anbehav.2003.08.021