Social organization of cooperatively breeding long-tailed tits: kinship and spatial dynamics

1. Long-tailed tits Aegithalos caudatus L. are cooperative breeders in whic h breeders that have failed in their own breeding attempt become helpers at the nest of relatives. We investigated the effects of kinship on the spati al dynamics of non-breeding flocks of long-tailed tits in order to determin e the information available on the kinship of other members of the populati on from their use of home ranges. 2. A novel method of home range analysis was devised based on 'convex hull peeling'. This method takes into account the dispersion of all fixes within a home range and permits the quantitative analysis of home range use. In a ddition, the method allows the extent of overlap between adjacent home rang es to be determined and the use of those areas to be investigated. 3. Non-breeding flocks of long-tailed tits were composed mainly of relative s, but also included unrelated immigrants. Flock ranges were large and ther e was extensive overlap between adjacent flocks. 4. The degree of range overlap was significantly affected by the relatednes s of flocks. If two flocks contained close relatives they were more likely to overlap than two flocks containing non-relatives. Moreover, the amount o f overlap was significantly greater for two adjacent related flocks than fo r two adjacent unrelated flocks. 5. The use of overlapping areas of non-breeding ranges of long-tailed tit f locks was also influenced significantly by relatedness. Overlapping flocks that were unrelated to each other usually avoided areas of overlap, while r elated flocks did not generally show such avoidance behaviour. 6. Kinship has significant effects on the spatial dynamics of non-breeding flocks of long-tailed tits and therefore flock behaviour can provide inform ation on the relatedness of other members of the population that might be i mportant for helping decisions in this cooperatively breeding species.