Lloyd, P., T. E. Martin, A. Taylor, A. Braae and R. Altwegg. 2016. Age, sex, and social influences on adult survival in the co-operatively breeding Karoo scrub-robin. Emu 114: 394-401.
Abstract
Among cooperatively breeding species, helpers are hypothesised to increase the survival of breeders by reducing breeder workload in offspring care and increased group vigilance against predators. Furthermore, parental nepotism or other benefits of group living may provide a survival benefit to young that delay dispersal to help on the natal territory. We tested these hypotheses in the Karoo scrub-robin (Cercotrichas coryphaeus), a long-lived, facultative cooperatively breeding species of southern Africa in which male offspring delay dispersal until they obtain a breeding vacancy in a nearby territory, and helpers make substantial contributions to parental care. The hypothesis that helpers improve breeder survival was not clearly supported; annual apparent breeder survival in the presence of helpers (0.82) did not differ detectably from breeders without helpers (0.77). Survival of breeders that lost helpers (0.71) was lower, which may reflect a benefit of helpers or a poor territory. The hypothesis that helpers may gain a survival benefit from deferred breeding was not supported; male helpers had similar apparent survival as male breeders in the first year, and lower survival thereafter. Nonetheless, the relatively high survival of males through the first year following fledging (0.50) or independence (0.65) is consistent with high juvenile survival among species with delayed dispersal.