The quality of social relationships affects male health in a complex bird society

Some animal societies, particularly in primate and corvid species, are based on enduring social bonds, based on sophisticated cognitive skills. A key unresolved issue for understanding the evolution of complex sociality and the associated advanced cognition is to uncover the fitness advantages that social relationships convey to individuals. Here, we investigated whether the social environment and the quality of individuals social relationships in captive groups of carrion crows affect excretion patterns of coccidian oocysts, which have been shown to exert detrimental consequences on bird health. In females, variables relating to the social environment and the quality of individuals social relationships did not have a strong influence on the occurrence of coccidian oocysts. However, male crows with strong social bonds and with a large number of relatives in their group were less likely to excrete feces containing coccidian oocysts. Thus, our data present evidence that high quality social relationships help male carrion crows to keep endo parasite burden low, suggesting that the social life might have potential fitness advantages by reducing parasite burden. Ultimately, these advantages might be important in driving the evolution of complex group living.