Social structure of Coal Tits Periparus ater in temperate deciduous forest

Abstract

Analysis of the impacts of social structure on the behaviour and life history of birds is a rapidly developing area of ornithology. Such studies commonly focus on the Paridae (tits and chickadees) as a model group, but detailed assessment of the basic social structure is lacking for many parids, particularly in the non-breeding season. Such baseline information is essential for understanding the organisation of bird populations, including associations between individuals within social and spatial networks. We assessed the non-breeding (autumn–winter) social structure and that during spring (i.e. the breeding season) for Coal Tits Periparus ater in broadleaved forest in southern Britain. Coal Tits were found to be resident and sedentary in this habitat, with birds remaining close to their spring territories during the non-breeding season and associating in small groups averaging 3–4 individuals. Associations were variable, however, with no evidence of stable flock membership, group territoriality or strong pair bonds during autumn–winter. The non-breeding social structure during a year of high population density did not differ from that during a year of low population density, being most similar to a ‘basic flock’ organisation. This contrasted with that predicted for a food-hoarding parid, highlighting the potential differences in social behaviour between different populations of bird species. Such variation in social behaviour can inform our understanding of the evolution of avian social structures and associated behavioural traits, such as food hoarding, and aid the interpretation of intra- and interspecific differences in behaviour.