Why would female birds be larger than male birds?
We do not know all the answers to this question yet, but here are some things to think about. When the male and female bird are significantly different sizes, they compete less when they are hunting. To provide better for their young, it is best if they hunt different kinds of prey. This also means that if one prey source is very thin one year, the other bird can still support the young. For example, if a disease decimates the mouse population, a male Red-Tailed Hawk will have less success hunting, but the female Red-Tailed Hawk can still catch rats and gophers to feed the family. Likewise, if larger prey became scarce, the male hawk would be better suited for catching small prey than the female, to support the family.
