Hackler, T. W. | Search bioRxiv

bioRxiv2024

Individual contributions to nest building and incubation by cooperatively breeding American Crows

American Crows (Corvus brachyrhynchos brachyrhynchos) are long-lived birds with pair bonds that may last many years. Pairs in Stillwater, OK, nested singly or in groups with up to 10 auxiliaries (Caffrey and Peterson 2015). Breeders did most of the nest building. Pair members contributed at approximately equal rates, although the sexes differed slightly in details: males tended to carry sticks and hand off materials more often, and females spent more time at and in nests. Both sexes worked faster on second and third attempts than on first attempts of the season. We found no evidence that pair members were (sexually) signaling to each other via their contributions. Incubation periods were characterized by low levels of activity at nests, where females spent most of their time and were fed once every 3-4 hours, mostly by their mates. Contributions to both stages of nesting by auxiliaries varied widely and exhibited no patterns with respect to any measured phenotypic characteristics.

ecology↗

bioRxiv2024

Nestling-care decisions by cooperatively breeding American Crows

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.

ecology↗