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While infection and perceived infection risk can influence social and reproductive behavior in several taxa, relatively little is known about how infection specifically affects pair bond behaviors. Some pair bond maintenance behaviors may be costly to maintain during infection, and infection could promote avoidance behaviors within an established pair. Many species exhibiting pair bonds are part of larger social groups, and behavioral shifts in established pairs can result in altered extra-pair contact rates that could also shape disease transmission. Using captive zebra finches (Taeniopygia guttata), we examined how an immune challenge with lipopolysaccharide (LPS) influences activity, social behavior, and pair bond maintenance behaviors in established pairs and their healthy neighbors. We observed shifts in individual and pair maintenance behaviors in both immune-challenged pairs and healthy pairs exposed to a social cue of infection (sick conspecifics). Specifically, LPS-challenged birds decreased activity and social interaction attempts relative to control birds, consistent with LPS-induced sickness behavior. LPS-challenged birds also increased the frequency of clumping (perching together in bodily contact) between individuals within a pair. Healthy birds exposed to immune-challenged conspecifics decreased flight activity and increased self-preening, behaviors which could function to limit infection risk. Exploring how both infection and the perceived risk of infection shape behaviors within and among paired individuals will increase our understanding of the role of social behaviors in shaping disease dynamics.

Across multiple species of social mammals, a growing number of studies have found that individual sociality is associated with survival. In long-lived species, like primates, lifespan is one of the main components of fitness. We used 18 years of data from the Lomas Barbudal Monkey Project to quantify social integration in 11 capuchin (Cebus capucinus) groups and tested whether female survivorship was associated with females’ tendencies to interact with three types of partners: (1) all group members, (2) adult females, and (3) adult males. We found strong evidence that females who engaged more with other females in affiliative interactions and foraged in close proximity experienced increased survivorship. We found some weak evidence that females might also benefit from engaging in more support in agonistic contexts with other females. These benefits were evident in models that account for the females’ rank and group size. Female interactions with all group members also increased survival, but the estimates of the effects were more uncertain. In interactions with adult males, only females who provided more grooming to males survived longer. The results presented here suggest that social integration may result in survival-related benefits. Females might enjoy these benefits through exchanging grooming for other currencies, such as coalitionary support or tolerance.

Allo-grooming networks in primate social groups are thought to have favored the evolution of vocal recognition systems, including vocal imitation in humans, as a more effective means of maintaining social bonds in large groups. Select avian taxa converged on vocal learning, but it is not clear what role analogues of allo-grooming might have played. Unlike allo-grooming in most primates, allo-preening in birds is usually limited to pair-bonds. One exception to this is during nestling development when siblings preen each other, but it is unknown how allo-preening influences vocal learning. We addressed this question in wild Green-rumped Parrotlets (Forpus passerinus) in Venezuela. Nestlings learn signature contact calls from adult templates. Large broods, age hierarchies and protracted development in this species create the potential for complex allo-preening networks and a unique opportunity to test how early sociality makes the development of vocal learning labile. From audio-video recordings inside nest cavities and a balanced design of different brood sizes, we quantified allo-preening interactions between marked nestlings, to compare to signature contact calls. Controlling for brood size and age hierarchy, the propensity to preen a larger number of individuals (i.e., out-strength) correlated positively with the age at first contact call. Allo-preening and acoustic similarity matrices did not reveal clear correlations within broods, instead larger broods produced greater contact call diversity. Results indicate that allo-preening elongates the period during which contact calls develop, which might allow individuals time to form a unique signature under the computationally challenging social conditions inherent to large groups.

Resource competition among conspecifics is central to social evolution, as it serves as one of the primary selective pressures of group living. This is because the degree of competition for resources impacts the costs and benefits of social interactions. Despite this, how heterogeneity in resource competition drives variation in the type and quantity of long-term social relationships individuals foster has been overlooked. By measuring male mating competition and female foraging competition in a highly social, long-lived mammal, we demonstrate that individual variation in long-term intrasexual social relationships covaries with preferred habitat and experienced resource competition, and this effect differs based on the sex of the individual. Specifically, greater resource competition resulted in fewer social preferences, but the magnitude of the effect varied by both habitat and sex, whereas for social avoidances, both the directionality and magnitude of the effect of resource competition varied by habitat and sex. Together our work shows how fine-scale variation in individual socioecological niches (i.e., unique physical and social environments) can drive extensive variation in individual social behavior (here long-term relationships) within a population, thereby broadening current theories of social evolution.

Anthropogenic disturbances are widely recognized for their far-reaching consequences on the survival and reproduction of wildlife, but we understand comparatively little about their effects on the social lives of group-living animals. Here we examined these short-term changes in affiliative behavior as part of a long-term study on a human-tolerant and socially flexible population of California ground squirrels (Otospermophilus beecheyi). We used social network analysis to examine short-term changes in affiliative behavior and individual consistency in response to disturbances by humans, domestic dogs, or a natural predator (the coyote). Overall, juveniles were more involved than adults in affiliative interactions, but the short-term directional effects of these acute disturbances on social cohesion varied by disturbance type. Human and dog presence reduced aboveground connectivity, particularly for juveniles, whereas disturbances by coyotes generally promoted it. Beyond these effects, we also detected non-random responses to disturbances, though individuals were not very consistent in their directional response to different disturbance types. Our results demonstrate the flexible changes in social behavior triggered by short-term disturbances imposed by humans and other threats. More generally, our findings elucidate the underappreciated sensitivity of animal social interactions to short-term ecological disturbances, raising key questions about their consequences on the social lives of animals.