The social integration of European badger (Meles meles) cubs into their natal group

Rebecca J. Fell, Christina D. Buesching1) & David W. Macdonald (Wildlife Conservation Research Unit, Dept. of Zoology, Oxford University, Abingdon Road, Tubney, OX13 5QL, UK)

(Accepted: 23 March 2006)

Summary Three main reasons have been suggested to explain the evolution of stable social groups in mammals: cooperation, resource dispersion, and natal philopatry. Here, we investigate the driving forces behind the social integration of badger Meles meles cubs into their natal group as a model for those species, where group-living has been attributed to ecological constraints. Between March 1995 and June 1996, we observed the cub/adult interactions of 9 litters in 2 badger social groups in Wytham Woods, Oxfordshire, from the time of their first emergence to full independence using remote controlled IR-video surveillance equipment. Our results show that with increasing age, cubs emerge earlier from the sett, interact with an increasing number of adults, and initiate a greater proportion of social interactions. Young cubs exhibit a specific behaviour (here termed ‘scent-theft’) to mark themselves with the subcaudal gland secretion of adult group-members, shown to carry group-specific information. In contrast to other social carnivores, badger cubs are not the focus of attention from adult group-members, but, supporting our hypothesis, their social integration into the natal group is gradual and cub-driven.

Keywords: offspring retention, social integration, natal philopatry, scent-marking, group- odour, group-living, badger.

Introduction Three main, and non-exclusive, explanations have been proposed for the formation of stable social groups (e.g., Emlen, 1982; Gittleman, 1989): firstly, the advantage of cooperative behaviours between group-members

1) Corresponding author’s: e-mail address: christina.wild-spirits.com © Koninklijke Brill NV, Leiden, 2006 Behaviour 143, 683-700 Also available online - www.brill.nl 684 Fell, Buesching & Macdonald

(e.g., cooperative hunting: Kruuk, 1975; Gittleman, 1989; cooperative de- fence against predators: Rood, 1975; Rasa, 1986; cooperative breeding and alloparental behaviour: Rood, 1990); secondly, the resource dispersion hy- pothesis, which postulates that the pattern of resource availability may fa- cilitate group-formation at low or even no extra cost (Macdonald, 1983; Macdonald & Carr, 1989); and thirdly, natal philopatry, where young are retained in the maternal territory due to ecological constraints on their dis- persal (Emlen, 1982; Lindstrom, 1986). Whereas the first hypothesis emphasises the resulting benefits of offspring retention for all group-members, the later two argue that the resulting bene- fits for the offspring outweigh the costs to existing group-members. As syn- thesised by, e.g., Macdonald et al. (2004a), the sociological benefits of social- ity in the framework of costs and benefits are ultimately determined by eco- logical factors. The balance of these sociological and ecological factors will determine the likelihood that existing group members will either welcome, merely tolerate, or reject new recruits, and will also determine the extent of the recruits’ efforts to join the group (Macdonald & Carr, 1989). The dif- ferent costs and benefits affecting each individual group member, and each recruit, should therefore be reflected in the social dynamics between them during the process of integration. In this paper we will describe the underly- ing behavioural mechanisms of adult-offspring interactions in the European badger Meles meles as a model. Within the order of the Carnivora, and the mustelid family in particu- lar, social organisation varies widely from solitary species (e.g., Mustela vison: Yamaguchi et al., 2004), to monogamous pairs (e.g., Aonyx capen- sis: Estes, 1989), spatial groups (Lutra lutra: Kruuk, 1995) to highly inte- grated group-living (e.g., Aonyx cinerea: Mason & Macdonald, 1986). One mustelid species, the Eurasian badger (Meles meles) displays all of these variants, its flexible social system (Johnson et al., 2000) ranging from solitary or pair-living individuals in Scotland (Kruuk & Parish, 1982) and parts of continental Europe (e.g., Goszczynski, 1999) and Japan (Yamamoto, 1995) to large, highly stable social groups of over 25 individuals in southern Eng- land (Rogers et al., 1998; Macdonald & Newman, 2002). This variability, together with the fact that intensive research has not yet revealed compelling evidence of cooperative behaviour beyond that of mutual grooming in this species (Johnson et al., 2004), make badgers an interesting model species for studies of social behaviour (Kruuk, 1989).