Effect of Site Fidelity on Cooperative Breeding in the Long-tailed Tit Aegithalos caudatus

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We examined whether a low site fidelity has an effect on group territoriality and the occurrence of helpers in the Long-tailed Tit Aegithalos caudatus. This species was seen all the year round, except for summer, at the edge of Kasuga-yama Woody Hills in Joetsu City, but none of the banded birds were residents. Winter groups were stable in membership but on one occasion two groups joined together. Group territorialism was loose because winter home ranges overlapped each other and few aggressive interactions were observed. Pairs were formed not only within but also between groups. Helpers were all failed breeders and some were from different winter groups. Typical cooperative breeders are seen among resident birds which live in groups all the year round. Although Long-tailed Tits in our area were not residents, the birds still expressed cooperative breeding. We conclude that a strong site fidelity may be a necessary condition for group territoriality but it is not a prerequisite for helping behaviour in this species.
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