Competition among individuals over shared resources reveals asymmetries in quality resulting in the formation of dominance hierarchies. These hierarchies act as a mechanism for social selection by partitioning resources among group-living animals. The following chapters describe my dissertation research which investigates the factors contributing to competitive asymmetries among broodmates as well as the short- and long-term consequences of the early social environment for the cooperatively breeding red-cockaded woodpecker (Picoides borealis). My research revealed that fledgling red-cockaded woodpeckers form male-biased, linear dominance hierarchies. Among fledgling males,, high relative nestling condition strongly predicted fledgling dominance, and this condition–rank relationship persisted through independence. Male nestlings are slightly larger and heavier than females; however, the sexual size dimorphism in mass is only present in mixed-sex broods, suggesting that the subtle structural size advantage gives males a competitive advantage over their sisters. Conflict rates among siblings increased with decreasing targeted feeding rates, and dominant fledglings were able to secure more food from provisioning adults through scramble competition. First-year survival favored males over females and dominant males over subordinates. Females were more dispersive overall than males, and subordinate males were more likely to disperse than dominants. The social environment prior to fledging influenced male dispersal decisions and subordinates delayed dispersal in the spring in situations where all dominants died over the winter. The probability of delayed dispersal in females was higher for females raised without brood-mates in one of two populations included in a long-term demographic data analysis. The availability of breeding vacancies may explain the differences in female dispersal behavior according to social environment between these populations. This research contributes to a greater understanding of the relative contribution of intrinsic benefits versus extrinsic constraints as an influence on delayed dispersal decisions in red-cockaded woodpeckers. Inter- and intra-sexual social rank is correlated with individual access to natal food resources and the probability of first-year survival. The intrabrood variation in dispersal strategies driven by social rank is sufficient to regularly produce both dispersal strategies among males and provides additional support that delaying natal dispersal is the preferred strategy for males in this system. / Ph. D.

Studies of mating systems and social organisation have been central to understanding of the evolution of social behaviour. The European badger Meles meles is a good species in which to study these processes, as its complex social system provides an opportunity to investigate how both natural and kin selection shape the evolution of mating systems and social structure. In this thesis, I use behavioural and genetic data to describe the mating system and social organisation of a high-density badger population and examine the occurrence of cooperative breeding. I genotyped 915 (85%) badgers trapped in Wytham Woods (1987–2005), 630 of which were cubs, and assigned both parents to 331 cubs with 95% confidence. This revealed a polygynandrous mating system, with up to five mothers and five fathers per social group. Mounting behaviour was also polygynandrous and I show the strongest evidence to date for multiple-paternity litters. I demonstrate, for the first time, that groups consisted of close and distant kin: approximately one third of group members were first-order kin, and overall group members had slightly lower relatedness levels than half-siblings. Within groups, adult and yearling females had higher pairwise relatedness than males, and neighbouring groups contained relatives. These findings result from the high level (42%) of extra-group paternities, 86% of which were assigned to neighbouring males. For the first time I show that females avoided inbreeding by mating with extra-group males; however, incestuous matings did occur. Promiscuous and repeated mountings were observed, which may reduce male–male aggression and infanticide, but may also promote sperm competition, genetic diversity, and / or genetic compatibility. Just under a third of adult males and females were assigned parentage each year and I quantify, for the first time, reproductive skew within badger groups. Correlations between relatedness, group productivity, and reproductive skew were not consistent with the predictions of incomplete-control models; rather, resource availability may play a role. Older and younger badgers displayed reduced annual breeding success, with male success increasing initially with experience. The Restraint, Constraint, and Selection Hypotheses did not explain the age-related breeding pattern in females. Variance in lifetime breeding success (LBS) was greater for males. Males that only bred within or only outside of their groups had half the LBS of males that did both. Females that were assigned maternity probably bred cooperatively and allonursed non-offspring, which has not been demonstrated previously. No benefit was established, however, in terms of litter size, probability of offspring breeding, or offspring lifetime breeding success, with more mothers in a group. In conclusion, badger social groups are fostered through kinship ties. Polygynandry and repeated mounting may have evolved originally to reduce male–male aggression and infanticide by males, through paternity masking. Although plural breeding occurs, group living appears to be costly. Motivation to disperse may be reduced through high-levels of extra-group paternities, which may also reduce inbreeding. Cooperative breeding among mothers may represent a low-cost behaviour with indirect benefits due to high levels of relatedness between female group-members. Badger sociality therefore represents an early stage in the evolution of social behaviour.