Details

Autor(en) / Beteiligte

• de Almeida Broom, Lara Natacha

Titel

The Effect of Helpers on the Post-Fledging Period of a Cooperatively Breeding Bird, The Sociable Weaver

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2014

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• To understand the evolution of cooperation it is crucial to determine the costs and benefits of this type of behavior. In cooperatively breeding species non-breeding individuals assist in raising offspring, and these ‘helpers’ are expected to increase reproductive output and/or breeders survival. While the effect of helpers on nestling conditions and breeders survival has been well studied, the effect of helpers on fledgings are rarely studied, mostly because of the difficulty in tracking mobile young. However, it has been suggested that besides improving juvenile future survival and dispersal probabilities, helper’s presence might also have costs to the young. We monitored juvenile survival during the first three months of life in sociable weavers, Philetairus socius, raised in pairs alone versus pairs with helpers, and used capturemark-recapture methods to control for individual detectability and estimate survival. Our results suggest a lower survival probability for juveniles with helpers from 17 to 30 days of age. Group size also seems to affect negatively survival. This is most likely true mortality, and not confounded by dispersal, since dispersers younger than 4 months are extremely rare. Colony size also seems to have a negative impact on juvenile survival, whilst rainfall has a positive effect. In order to understand this effect we investigated if juveniles with helpers fledged earlier using temperature inside the nest as a proxy for fledging date; however found no indication of significant differences. We also investigated if the breeders re-nesting interval after a successful brood could be shorter for parents with helpers, but also found no significant effect. Despite of this, our study gives new insights into the effects of helpers on the post-fledging period of cooperative breeders, demonstrating a cost that has now to be understood.