The effect of helping behaviour on the survival of juvenile and adult long-tailed tits Aegithalos caudatus

1. In the cooperative breeding system of the long-tailed tit Aegithalos caudatus failed breeders may become helpers at the nest of another pair to whom they are usually related. The aim of this study was to determine the effect of helping behaviour on the survival of helpers and the recipients of their help. 2. We used capture-mark-recapture data and the MARK program to analyse survival of 482 birds ringed as fledglings and 155 birds ringed as adults. 3. Juvenile males had a higher survival probability than juvenile females across all years whilst their subsequent adult survival was constant. Within sex, the survival probability of juveniles that fledged from nests with helpers was higher than those that did not receive help as nestlings. 4. Failed breeders that became helpers had a higher survival probability (56%) than those failed breeders that did not become helpers (46%). Successful breeders had a survival probability of 56% regardless of whether they received help or not. 5. Failed breeders that became helpers had a lower probability of successfully breeding in a subsequent year (27%) when compared to those failed breeders that did not become helpers (38%). 6. We conclude that helpers gain kin-selected fitness benefits through the increased survival of related offspring but not through the increased survival of related breeders. Furthermore, helpers gain direct fitness benefits through increased personal survival, but at a cost of reduced probability of successful future personal reproduction.