Enhanced Reproductive Success of Female Black-Capped Chickadees Mated to High-Ranking Males

Abstract

Overwinter survival of female Black-capped Chickadees (Poecile atricapillus) depends in part on the rank of their mates. We investigated whether females also gain re- productive benefits by pairing with high-ranking males. We assessed breeding success in 1993 to 1995 and 1997 by comparing clutch size, proportion of eggs hatched, hatching date, and predation rates on nests of females mated to either high-ranking or low-ranking males. We also compared feeding rates of males to incubating females and to offspring during the early nestling period in 1994 and 1995. High-ranking and low-ranking males did not differ in feeding rates during early incubation or early nestling stages. Females mated to high- ranking males incubated for longer periods than females mated to low-ranking males. Youn- ger males and females mated to low-ranking males fed nestlings at a higher rate than did older males and females mated to high-ranking males, respectively. Females mated to high- ranking males had larger clutches, hatched a significantly greater proportion of their eggs, and suffered lower nest predation than females mated to low-ranking males. In 1995 and 1997, where the ranks and ages of both members of 23 pairs were known, female rank was strongly correlated with mate rank and age but was only weakly associated with female age. Female rank accounted for significant variation only in clutch size, and male rank accounted for a greater proportion of variation in clutch size and fledging success than did the female's