Females may refuse to mate with mated potential partners or harm rival females. Pregnancy block in some species of mice is a good example of this. Birds tend to be monogamous whereas mammals tend to be polygamous. Predicts that females who mate with multiple males will be more likely to have viable young. To forage there requires mating with him.
Males control access to multiple females.
Resource-defense Polygyny . Males control access to females indirectly by monopolizing critical resources. A female may have a better chance of producing viable offspring by choosing a male who already has a female in his territory. Allows males to pool their displays so they can be heard from a distance, for example. Males search out mates but don t overtly compete for them.