| dc.description.abstract | In cooperatively breeding societies, where individuals (termed ‘helpers’) provide care to young which are not their own, group members can vary substantially in their contributions to cooperative activities. Individuals are expected to exhibit higher levels of cooperative investment if the benefit of performing that behaviour greatly outweighs the cost of performing that behaviour. This may be achieved by directing investment towards kin (thereby maximising indirect fitness benefits) and/or attaining large direct fitness benefits. In this thesis, I explore whether direct fitness benefits shape patterns of helping behaviour in the cooperatively breeding white-browed sparrow weaver (Plocepasser mahali). White-browed sparrow weavers live in year round territorial groups with high reproductive skew, comprising a dominant pair and subordinates of both sexes. Although all group members contribute to a wide range of highly conspicuous cooperative activities, there is large inter-individual variation in investment. In chapter 2, I use simulated territorial intrusions to show that sexually-selected direct benefits shape the expression of sentinel behaviour. In chapter 4, I provide evidence that the direct benefits associated with either the pay-to-stay or social prestige hypotheses are unlikely to modulate patterns of provisioning in male white-browed sparrow weavers. Evidence of marked individual differences in contributions to offspring care in cooperative societies is also generating increased interest in the proximate causes of such variation. In chapter 5, I use within-individual measurements to demonstrate that variation in provisioning effort is not directly regulated by variation in circulating levels of prolactin (a pituitary hormone). The evidence does suggest, however, that provisioning behaviour may be induced by exceeding a threshold hormone level. Individual contributions to parental behaviours (as opposed to alloparental) may be shaped by constraints associated with life-history traits. In chapter 3, I show that parents in white-browed sparrow weaver societies perform different provisioning rates yet employ similar food allocation tactics, and that these patterns are expected in tropical living bird species. Combined, these findings provide insights into the selection pressures that may shape individual contributions to cooperative activities. | en_GB |
