Symbiotic microbiota vary with breeding group membership in a highly social joint-nesting bird

Symbiotic microbes affect the health, fitness, and behavior of their animal hosts, and can even affect the behavior of non-hosts. Living in groups presents numerous benefits and challenges to social animals, including exposure to symbiotic microbes, which can mediate both cooperation and competition. In social mammals, individuals from the same social group tend to share more similar microbes and this social microbiome, the microbial community of all hosts in the same social group, can shape the benefits and costs of group living. In contrast, little is known about the social microbiome of group living birds. We tested the predictions that communally breeding smooth-billed anis (Crotophaga ani) belonging to the same breeding group share more similar microbes and that microbial community composition differs between body regions. To test this, we used 16S rRNA gene sequencing to characterize the preen gland and body feather microbiota of adult birds from 16 breeding groups at a long-term study site in southwestern Puerto Rico. As predicted, individuals from the same breeding group shared more similar microbiota than non-group members and preen gland and body feathers harbored distinct microbial communities. Future research will evaluate whether this social microbiome affects the behavior of group living birds. All animals host bacteria that can be helpful or harmful, and can even affect behavior. Animals living in groups might share bacteria, which could influence cooperation and competition. We tested whether bacteria were more similar among group members in a communally breeding bird, the smooth-billed ani. Group members had more similar bacteria than non-group members, and different body regions had different bacteria. Our next steps are to test whether these shared bacteria affect group behavior.