Richard Dawkins. The selfish gene (№ 237359)

As I said, the female is also advantageous to the courtship process, the male brought her food.
In birds is usually considered as a kind of return to the juvenile behavior on the part of females. Begging for food from the male, she accompanies this movement, typical for young birds. It was assumed that such behavior automatically attract a male, just as the man seems attractive when a grown woman babbles or purses her lips like a child.