Abstract
In group living animals behavioural interactions with conspecifics strongly modulate an individual’s physiological stress response. A secure social embedding, with stable social relationships is expected to dampen an individual’s stress response which is in turn will affect the immune system and health. Ultimately, positive health effects of stable social bonds may contribute to maintain group living. We investigated whether, in cooperatively breeding carrion crows (Corvus corone), the quality of social relationships have measurable effects on patterns of gastrointestinal parasite product excretion. We repeatably collected behavioural data on dyadic social interactions and individual droppings to quantify parasite products, from 34 individuals in a captive population of carrion crows in northern Spain. Individuals with strong social bonds and living with more related individuals in a group, excreted less samples containing coccidian oocysts. Sex, group size, number of social bonds and dominance rank had no significant effect on number of samples containing coccidian oocysts. Also, the likelihood to excrete samples containing nematode eggs was not affected by any of the factors we considered. Our data presents evidence for affiliative social relationships to be linked to coccidian oocyst excretion, indicating that the social environment has strong fitness implications. This suggests that next to humans and other primate species, social relationships may be important in driving the evolution of complex sociality in a larger variety of taxa, including birds.