EXTRA-PAIR COPULATIONS IN SONGBIRDS Introductio

Studies demonstrate that female birds engage in copulations with males other than their mate and these extra-pair copulations (EPCs) may result in extra-pair fertilizations. The frequency of extra-pair paternity varies among populations or years within the same species. The question remains, regarding why females mate with more than one male (Dunn, Robertson, Michaud-Freeman, & Boag, 1994). To answer this question, researchers attempt to determine factors related to EPCs and propose theories regarding EPCs. Naturalistic, observational, and experimental studies confirm hypotheses regarding prevalence, adaptive functioning, sexual selection, and fledgling adoption.

DNA fingerprinting is used to examine the frequency of extra-pair copulation. Birkhead, Burke, Zann, Hunter, and Krupa (1990) studied 25 zebra finch (Taeniopygia guttata) families, with 16 pairs of parents and 92 offspring. The authors found ten cases of extra-pair parentage (10.9 percent of offspring or 36 percent of broods). Behavioral observation demonstrated that extra-pair parenting occurred through extra-pair copulation and not rapid mate switching. DNA fingerprinting also reveals an increase in levels of extra-pair paternity from the previous year for monogamous tree swallows (Tachycineta bicolor); 50 percent of the broods had extra-pair young in 1990, compared to 87 percent found in 1991 (Dunn, Robertson, Michaud

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consistent with female choice for male genetic quality. Males can increase their mating success in monogamous birds by engaging in extra-pair copulations (Dunn & Robertson, 1993). Early studies suggested that males harassed and forced copulation with females, however recent studies find that females appear to gain from participating in extra-pair copulations and fertilizations (Hasselquist, Bensch, & von Schantz, 1994). Stutchbury, Rhymer, and Morton (1994) report their findings regarding extra-pair fertilizations of the hooded warbler, a monogamous songbird. DNA fingerprinting revealed that 47 percent females had extrapair young in their first or second brood and 29 percent were the result of extra-pair fertilizations. Extra-pair young were more frequent in first broods and the proportion within a brood was strongly bimodal among broods. Adjacent male neighbors were sometimes identified as the father. It was concluded that females benefit from extra-pair copulations and have some control over which males obtain EPCs. Lifjeld and Robertson (1992) demonstrated female control of extra-pair copulation. The authors studied tree swallows and reported that unfaithful females copulate with their mate similarly to the rates of
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Some common words found in the essay are:
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Approximate Word count = 1400
Approximate Pages = 6 (250 words per page)