Extra-Pair Paternity in the Black-Capped Chickadee

Abstract

Studies of the mating strategies of birds are increasingly shifting their focus to the role that females take in controlling copulation (Hunter et al. 1993, Petrie 1992, Birkhead and Moller 1993). In some avian species, females appear able to control whether copulations occur by accepting or rejecting copulation attempts (BjSrklund et al. 1992, Lifjeld and Robertson 1992, Westneat 1992). Similarly, females of some species actively solicit copulations by seeking the extra-pair male in his own territory (Smith 1988, Kempenaers et al. 1992, Venier et al. 1993). In species where females do control the outcome of copulation attempts, there is a need to, first, determine the extent that extra-pair copulations (EPCs) lead to fertilizations and, second, establish potential benefits that a female may obtain by engaging in EPCs. Smith (1988) reported that female Black-capped Chickadees, Parus atricapillus, seek EPCs from males on territories adjacent to the territory defended by the female's mate. Interestingly, Smith observed that females preferentially sought males for EPCs that held higher dominance rank than the female's mate in the preceding winter's flock. Thus, female Black-capped Chickadees may be engaging in a mixed reproductive strategy of social monogamy while increasing reproductive success by extra-pair copulations with males of higher genetic quality than their own mate (Trivers 1972, Smith 1988, Hamilton 1990). Females may also benefit from engaging in EPCs with dominant males if, by doing so, this facilitates rapid pair bonding with the dominant male in the event that his mate dies. There is a need for data on whether EPCs are resulting in extra-pair paternity of the nestlings in order to imply a fitness benefit to the female's behavior. In this study we document rates of extra-pair paternity in an Ontario population of Black-capped Chickadees, using DNA fingerprinting, and provide support for Smith's hypothesis by showing that extra-pair males were of higher dominance rank than the female's mate. We also suggest a paternity-related explanation for occasional observations ofpolyandry in chickadees (Waterman et al. 1989, Howitz 1991).