Grooming time parallels molt intensity in wild-caught feral rock pigeons

Feathers are critical for locomotion, communication, thermoregulation, waterproofing, and protection from UV radiation. To maintain these functions, birds care for their feathers by grooming, which consists of preening with the bill and scratching with the feet. Grooming cleans and arranges feathers, distributes preen oil and powder down, and removes ectoparasites. Birds devote considerable time and energy to grooming, to the exclusion of other activities, such as foraging. All else being equal, birds should aim to minimize their grooming time. Seasonal changes in grooming have been documented, with some species of birds grooming more in summer than winter. The higher rate of summer grooming may be caused by molt; however, the relationship between the dynamics of grooming and molt have been quantified only in captive birds subject to other manipulation, such as induced molt in poultry, or access to mates in zebra finches. We conducted an eight-month study of wild-caught feral rock pigeons Columba livia to compare rates of grooming and molt. We found that the intensity of grooming parallels the intensity of molt throughout the molt cycle. Pigeons more than double their grooming time at peak molt, consistent with patterns observed in wild birds. Our results suggest that molt may be more energetically costly than previously realized, given concomitant increases in grooming.