Covas R, Deville A-S, Doutrelant C, Spottiswoode CN, Gregoire A. 2011. The effect of helpers on the post-fledging period in a cooperatively breeding bird, the social weaver. Animal Behaviour 81:121-126

Abstract. Understanding the evolution of cooperation requires determining the costs and benefits of cooperative behaviour. In cooperative breeders, where nonbreeding individuals assist in raising offspring, these 'helpers' are expected to increase the fitness of breeders and hence empirical research has focused on the effect they have on reproductive output and breeder survival. However, the effects of helpers during the postfledging period are poorly known because of the difficulty of tracking fledglings in the wild. Helper presence might be beneficial for fledglings, for example through continuous food delivery or increased predator vigilance, but potential competition between helpers and fledglings, or changes in investment of parents assisted by helpers, could counteract these positive effects and have a negative influence on postfledging survival probabilities or promote dispersal. We investigated the survival of juvenile sociable weavers, Philetairus socius, raised in pairs alone versus pairs with helpers by using capture-mark-recapture methods to control for individual detectability in survival estimation. We found that local survival in the first year was reduced in young raised by groups versus those raised by pairs. This may reflect either higher mortality or emigration of juveniles raised in groups. Hence, our study reveals significant postfledging effects of cooperative breeding that have not been reported previously and that need to be investigated in studies addressing the evolution of cooperative breeding.

The Sociable Weavers were studied on Benfontein Game Farm near Kimberley, Northern Cape, and formed the basis of many studies. The number of chambers in many of the study nests were counted over several years and Rita has kindly provided these records for PHOWN (Photos of Weaver Nests), without photos however. These records may be viewed here - zoom in on the map in the vicinity of Kimberley.