In sickness and in health: group-living augments behavioural responses to food and predation risk for sick house finches (Haemorhous mexicanus).

Group-living provides many fitness benefits for individual members, including improved foraging and predator vigilance. If such benefits are especially pronounced for sick members, group-living can act as a form of behavioural tolerance by offsetting mortality costs of infection. We experimentally tested this possibility by examining whether group-living impacts foraging and anti-predator behaviours in house finches (Haemorhous mexicanus) with or without conjunctivitis caused by Mycoplasma gallisepticum. We varied both group-living (single-housed or group-housed) and infection (M. gallisepticum-inoculated or sham-inoculated) and performed four behavioural assays at peak infection: two assessing how birds respond to foraging opportunities and two assessing responses to predation threats. Both social treatment and disease status influenced most measured behaviours, with single-housed, diseased birds consistently the least responsive to foraging opportunities and predation threats. While group-living also benefited healthy individuals (e.g. led to faster responsiveness) in most behavioural assays, our results suggest that diseased birds particularly benefit from group-living. Further, detected behavioural differences with group-living were not explained by effects of sociality on disease severity or pathogen load, which did not differ with group-living. By augmenting behaviours key to survival during infection, group-living may act as a form of behavioural tolerance for social species, with important implications for transmission dynamics.