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. Females control access to multiple males. Extremely rare, but there are a few key examples in birds where males get stuck incubating the eggs.