Females increase reproductive investment in response to helper‐mediated improvements in allo‐feeding, nest survival, nestling provisioning and post‐fledging survival in the Karoo scrub‐robinCercotrichas coryphaeus

Abstract

In many cooperatively‐breeding species, the presence of one or more helpers improves the reproductive performance of the breeding pair receiving help. Helper contributions can take many different forms, including allo‐feeding, offspring provisioning, and offspring guarding or defence. Yet, most studies have focussed on single forms of helper contribution, particularly offspring provisioning, and few have evaluated the relative importance of a broader range of helper contributions to group reproductive performance. We examined helper contributions to multiple components of breeding performance in the Karoo scrub‐robinCercotrichas coryphaeus, a facultative cooperative breeder. We also tested a prediction of increased female investment in reproduction when helpers improve conditions for rearing young. Helpers assisted the breeding male in allo‐feeding the incubating female, increasing allo‐feeding rates. Greater allo‐feeding correlated with greater female nest attentiveness during incubation. Nest predation was substantially lower among pairs breeding with a helper, resulting in a 74% increase in the probability of nest survival. Helper contributions to offspring provisioning increased nestling feeding rates, resulting in a reduced incidence of nestling starvation and increased nestling mass. Nestling mass had a strong, positive effect on post‐fledging survival. Controlling for female age and habitat effects, annual production of fledged young was 130% greater among pairs breeding with a helper, and was influenced most strongly by helper correlates with nest survival, despite important helper effects on offspring provisioning. Females breeding with a helper increased clutch size, supporting the prediction of increased female investment in reproduction in response to helper benefits.