Forced Extra-Pair Copulation in the White-Cheeked Pintail: Male Tactics and Female Responses

Abstract

I studied tactics used by males to detect fertile females and achieve forced extra-pair copulations (FEPC) and female responses to FEPCs in a non-migratory, asynchronously breeding population of White-cheeked Pintails (Anas bahamensis) in the Bahamas. Males assessed female reproductive status by (1) monitoring behavior of neighboring pairs, (2) visiting the island nesting site and observing laying females directly, and (3) chasing females. FEPC attempts directed at neighboring females were more likely to occur during the female's fertile period than FEPC attempts directed at non-neighbors and a large proportion (44%) of FEPC attempts involved neighboring pairs. Sexual chases of fertile females were more frequent and of longer duration than chases of non-fertile females suggesting that males gain information on female reproductive status in initial chases. Males employed sophisticated tactics to achieve FEPCs, including waylaying females as they left their nests, approaching females surreptitiously by swimming "submarine" style, and capturing and mounting females underwater. Females vigorously resisted FEPC attempts by repeatedly diving, flying away and hiding and were sometimes chased to exhaustion. The high costs of resistance and observations that females resisted copulations from all extra-pair males, regardless of quality, make "resistance-as-a-ploy" and "genetic-quality" hypotheses unlikely explanations for why females resist EPCs. I argue that females resist EPCs to preserve the pairbond and investments of their mates, which in turn protects their investment.