Mycoplasmal conjunctivitis and the behavior of wild house finches (Carpodacus mexicanus) at bird feeders

Parasite infections can influence host foraging behavior, movement, or social interactions. House finches (Carpodacus mexicanus) in the US are susceptible to a recently emerged strain of the bacteria, Mycoplasma gallisepticum. Infected birds develop mild to severe conjunctivitis that could affect their foraging or social behavior. We videotaped house finches with and without conjunctivitis at a bird feeding station in Atlanta, GA to determine whether birds with conjunctivitis differed in feeding duration, efficiency, total food intake, or aggressive interactions. We observed 105 house finch feeding bouts (of which 41% were of birds with conjunctivitis). Infected birds spent more time at the feeding station and had smaller average and minimum flock sizes. House finches with conjunctivitis also showed lower feeding efficiency than noninfected birds in terms of seeds obtained per attempt and number of seeds eaten per unit time. However, because of their longer feeding bouts, birds with conjunctivitis consumed similar total numbers of seeds as birds without conjunctivitis. Finally, house finches with conjunctivitis were displaced from feeder perches less frequently than noninfected individuals and 75% of all observed displacement events consisted of an infected bird displacing a noninfected bird. Differences in flock sizes and feeding behavior of birds with and without mycoplasmal conjunctivitis could influence the fitness effects and transmission of this bacterium in wild house finch populations.