Forced copulation (a less sociologically-charged way of saying rape) is a common reproductive strategy in ducks and geese, but is much rarer in other types of animals. Gowaty and Buschhaus (1998) suggest that the threat of forced copulations may be a driving force in selecting for monogamy, at least in ducks and geese. In their model, by choosing to pair-bond with a male, the female gains the male's services in protecting her from forced copulations by other males. Females can also combat forced copulations by evolving methods of expelling or not using sperm gained in this way (Dunn et al. 1999). The evolutionary dynamics surrounding forced copulations are complex; Clutton Brock and Parker (1995) review the causes, costs, and modes of evading forced copulation.
Clutton-Brock T H, Parker G A 1995 Sexual coercion in animal societies Anim
Behav 49 (5): 1345-1365
Dunn PO, Afton AD, Gloutney ML, Alisauskas RT 1999 Forced copulation results
in few extrapair fertilizations in Ross's and lesser snow geese
Anim. Behav. 57: 1071-1081
Gowaty PA, Buschhaus N 1998 Ultimate causation of aggressive and forced copulation
in birds: Female resistance, the CODE hypothesis, and social monogamy Am. Zool.
38 (1): 207-225
Mckinney F, Derrickson S R, Mineau P 1983 Forced copulation in waterfowl Behaviour
Seymour N R 1990 Forced copulation in sympatric american black ducks and mallards
in Nova Scotia Can J Zool 68 (8): 1691-1696
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