Allopreening in the Black Vulture

Black Vultures (Coragyps atratus) regularly feed on offal during low tide on the muddy shore of the Surinam River in the center of Paramaribo. At high tide they rest on roofs of buildings along the waterfront where they spend the time sunning in a very upright stance with widespread wings and their backs to the sun, vigorously preening their feathers. On 22 January 1948, five vultures sat on a roof; two of them very close to eachother and almost touching, were preening busily. One nibbled the feathers of the lower neck of the other and the latter responded by nibbling the neck feathers of the first.

F. HAVERSCHMIDT, The Auk, 94(2)