No direct fitness benefits of helping in a cooperative breeder despite higher survival of helpers

Abstract

Helpers in cooperatively breeding species may gain direct fitness benefits that increase their survival probability and/or reproductive success. However, survival and productivity may be influenced by many other factors, including variation in dispersal, nepotistic interactions, or individual condition. High helper survival relative to nonhelpers has been reported in the long-tailed tit Aegithalos caudatus, a cooperative breeder where helpers are failed breeders that redirect care toward kin. Using capture-mark-recapture analysis of a long-term data set, we confirm this result and show that it is not attributable to differential dispersal. Then, using only males with first-order relatives (to control for any effects of nepotism), we investigated the survival of 3 groups of failed breeders (i.e., potential helpers): survival of helpers was highest (61%) but, contrary to predictions based on direct benefits, survival of 2 categories of nonhelpers differed; those with helping opportunities had the lowest survival rate (24%), whereas those without helping opportunities had intermediate survival (52%). We suggest that the groups varied in condition; helpers are in good condition, males with helping opportunities who did not help are in poor condition, and nonhelpers without helping opportunities comprise a mixture of birds in good and poor condition. This conclusion was supported by differences in the timing of breeding (a proxy for condition) between groups: helpers bred earliest and nonhelpers with helping opportunities bred latest. Furthermore, we found no evidence that helpers gained any future reproductive benefits. We suggest that condition rather than benefits accrued as a direct result of helping influenced helper survival. © The Author 2010. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved.