Nestling-care decisions by cooperatively breeding American Crows

Abstract

During the nestling stage of breeding seasons in Stillwater, OK, pairs of American Crows (Corvus brachyrhynchos brachyrhynchos) lived alone or in groups of variable composition; auxiliaries included individuals that had delayed dispersal, immigrated into groups, or returned to natal territories after having lived elsewhere. Most, but not all, auxiliaries contributed to feeding nestlings, and their contributions varied considerably. On average, breeders fed nestlings at greater rates than did auxiliaries, and female breeders spent more time at nests than did other group members. Breeders compensated for auxiliary contributions by reducing their own; this and breeder responses to the disappearance of auxiliary feeding group members provide evidence that these long-lived, iteroparous animals were managing energy budgets so as to maximize fitness over the long term. Female breeders in larger groups spent more time at nests than did those in smaller groups, but not for expected reasons and not to any reproductive benefit. A few female auxiliaries spent increasing amounts of time at nests as nestlings aged. No other measured phenotypic characteristic of individuals was found to explain any of the wide variation in the patterns of nestling care exhibited by members of our population.