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.

Intracellular glucocorticoid receptors in spleen, but not skin, vary seasonally in wild house sparrows (Passer domesticus)

“…life fights with conspecifics over mates and territory [30,31]. During this life-history stage, a short-term rise in CORT either due to an agonistic encounter [48] or immune activation [3] might facilitate re-allocation of leucocytes to the periphery and/or cause increased lymphocyte proliferation.…”

Does corticosterone regulate the onset of breeding in free-living birds?: The CORT-Flexibility Hypothesis and six potential mechanisms for priming corticosteroid function

“…Hypothesis may also apply. For example, male birds that spend much of the day singing in 526 conspicuous breeding plumage may be more obvious to predators (Gotmark and Post, 1996), and 527 may encounter more challenges from conspecifics resulting in injury (Townsend et al, 2011), 528 compared to non-breeding males. However, the most relevant of these three seasonal hypotheses 529 to pre-breeding corticosteroid physiology is probably the Behavior Hypothesis.…”

Apparent inbreeding preference despite inbreeding depression in the American crow

“…A pattern of apparent inbreeding preference emerged at all spatial scales examined, from the narrow, neighbourhood scale (0.6 km diameter), across which birds interacted on a daily basis, to the broadest local scale (4 km diameter), across which opportunities for crows to move and interact may have been constrained in the breeding season (Townsend, Clark, McGowan, & Lovette, ; Townsend et al., ). This pattern did not support our hypothesis that inbreeding would be avoided at the narrow, neighbourhood scale, where mate choice most likely occurs and which we predicted would be enriched with relatives.…”

“…Moreover, in winter months, the mean daily distance travelled from the communal roost to foraging sites in the California population was 7.7 ± 4.1 km (Taff et al., ), a distance longer than the diameter of the sampling area at this scale (4 km). However, movements could be more constrained in the breeding season, when most group members remain on their territories, which they vigorously defend against intruders (Townsend, Clark, & McGowan, ; Townsend, Clark, McGowan, & Lovette, ). Intermediate local scale (1.5 km diameter; solid circles, Figure ). Here, we included as “potential breeders” the adult, resident birds sampled within two smaller, nonoverlapping clusters of nests within each population (New York or California), each cluster having a 1.5 km diameter.…”

“…Moreover, in winter months, the mean daily distance travelled from the communal roost to foraging sites in the California population was 7.7 ± 4.1 km (Taff et al, 2016), a distance longer than the diameter of the sampling area at this scale (4 km). However, movements could be more constrained in the breeding season, when most group members remain on their territories, which they vigorously defend against intruders (Townsend, Clark, & McGowan, 2011;).…”