Allogrooming in primates serves not only a hygienic function, but also plays a crucial role in maintaining strong affiliative bonds between group members, which in turn, underpin the emergence of cooperative behavior. In contrast, although allopreening occurs in many avian species, we know little about its social functions. Our study addresses this issue by investigating allopreening in a broad comparative data set including six corvid and nine parrot species. We assessed whether rates of allopreening initiations, proportion of time spent allopreening, and the number of grooming partners in captive group-housed birds were comparable to patterns observed in captive chimpanzees and bonobos. While parrots and corvids were found to have similar rates of social grooming to bonobos and chimpanzees, Pan species dedicated significantly more time to social grooming. Animals in larger groups had more grooming partners, but when controlling for the number of potential partners, birds tended to have fewer grooming interaction partners than Pan species. We then investigated whether allopreening in parrots and corvids was predicted by behavioral markers of affiliative social bonds (close physical proximity, active feeding, and low levels of agonistic behavior). Results revealed that providing allopreening to a partner was significantly predicted by often being in close proximity, but not engagement in active feeding or agonistic behavior. We examined the region allopreened in a subset of species and found that preening a partner's head was predicted by both close physical proximity and active feeding, while body allopreening was only predicted by close physical proximity. Head preening may confer more hygienic benefits to recipients, and thus may be more selectively provided to valued partners.Results support the hypothesis that allopreening in corvids and parrots helps maintain social bonds with an individual's most important social partners, showing some similarities to allogrooming in primates.

Sex-segregation occurs in a number of mammals, and is typically attributed to differences in body size, reproductive energetics, or social roles. Although most primates remain in cohesive groups, spider monkeys exhibit fission-fusion dynamics and sex-segregated association patterns. Here, I present results on sex differences in behavior and subgrouping in juvenile spider monkeys. I found that the monkeys exhibit several aspects of sex-differentiated behavioral and grouping patterns that emerge despite the fact that both sexes ranged with their mothers. I conclude that juvenile spider monkeys exhibit sex-segregated behavior and association patterns earlier than previously reported for this species. Because the hypotheses regarding body size dimorphism and reproductive energetics do not apply to these juveniles, I attribute these differences to social roles.

Conversation is a skilled activity that depends on cognitive and social processes, both of which develop through adulthood. We examined the effects of age and partner familiarity on communicative efficiency and cortisol reactivity. Younger and older women interacted with familiar or unfamiliar partners in a dyadic collaborative conversation task (N = 8 in each group). Regardless of age, referential expressions among familiar and unfamiliar partners became more efficient over time, and cortisol concentrations were lower for speakers interacting with familiar partners. These findings suggest that communicative effectiveness is largely preserved with age, as is the stress-buffering effect of a familiar partner.