Injury and paternity loss in cooperatively breeding American Crows

Abstract

Although survivable injuries have been documented in several species of birds, little is known about the social and reproductive consequences of such injuries. We examined relationships between injuries and group composition, reproductive output, and paternity of male breeders in 27 family groups of American Crows (Corvus brachyrhynchos) using 96 broods sampled from 2004 to 2009. Injuries and permanent disfigurement of wings or feet were sustained by 25.9% (7/27) of dominant male breeders. Injured male breeders had smaller broods (2.13 vs. 3.38 nestlings per brood for injured vs. uninjured breeders), lost more paternity (48% vs. 13% extrapair young per brood), and had more adult male auxiliaries in their groups (1.63 vs. 0.65 auxiliaries per group) than uninjured birds. Some of the variation in reproductive partitioning, extrapair paternity rates, and group composition among American Crow family groups can therefore be explained by injuries to male breeders. These results suggest that injuries could account for some of the unexplained variation in the rates and distribution of extrapair paternity across populations and taxa, as well as some of the variation in reproductive skew among cooperatively breeding birds. © 2011 Association of Field Ornithologists.