Although parasitism is often considered a cost of sociality, the evidence is mixed, possibly because sociality is multivariate. Here we contrast the dependence of parasitism costs on major social variables such as group size and social structure, as measured by network metrics. We conduct two robust phylogenetic meta-analyses, comprising 43 published results for studies with group size and 32 results with social structure metrics. This is the first meta-analytical test of this hypothesis for mammals as a whole. Contrarily to theoretical expectations and previous meta-analyses, there is no relationship between group size and parasitism, but we find conflicting results when analysing different aspects of sociality. Our analysis reveals that social structure is connected to parasite load, possibly because contact between group members, and not group size, is linked to parasite transmission. While more intensely interconnected groups facilitate parasite transmission, large groups are frequently fragmented into smaller, weakly connected subgroups. Strong social modularisation should thus be favoured by natural selection to hamper parasite overload. Future empirical studies should focus on specific parameters of social network structure and on parasite transmissibility. If social structure can evolve fast, even culturally, then host/parasites evolutionary games enter into a whole new fast dynamics, and animal conservation studies should take advantage of this possibility.

Reintroduction processes, whereby animals are reared in captivity and released into the wild, often fail. This failure is often attributed to the fact that released individuals not have the behavioral repertoire to cope with the wild. Compared to captive conditions, wild environments are highly complex, and therefore a released individual with greater behavioral complexity may survive better after release. Moreover, the wild presents both unpredictable features and regular changes, and thus plasticity of behavior may be crucial for survival. Considering the importance of foraging to fitness, foraging complexity and plasticity can be crucial to the success of reintroduction processes. We investigated captive individuals of Eupsittula aurea (Psittaciformes, Psittacidae) to evaluate if: a) food enrichment promotes foraging complexity; and b) there is a relationship between foraging complexity and plasticity. An animal that potentially has a good adjustment to wild environments would be one that has high foraging complexity and plasticity. We housed 40 parakeets under identical conditions that differed only in their diet. Twenty birds, in four replicated enclosures, were randomly allocated to the treatment diet which better replicated what would occur in the wild and consisted of multiple entire fruits, and food spatial randomization. The remaining 20 birds were placed into four control enclosures and received a diet that is currently provisioned for birds in captivity and consisted of small fruit cubes and sunflower seeds, offered on tray at a fixed location. Dietary enrichment does not affect bird foraging complexity. According to our expectations, foraging complexity influenced foraging plasticity for birds that were subject to the enriched environment. Therefore, more extensive foraging repertoires are related to a greater adjustment capacity in enriched environments, and complexity could be considered a good measure of adjustment to reintroduction success.