When black kites build their nests, they're especially fond of white decorations, eschewing all other colors. That's because these "white flags" can be positioned to notify other birds about the nest-builder's age, territory size, and sexual prowess.
New research has revealed that the birds with the most scraps of white plastic woven in their nests produce the most babies, have the largest territories, and fight off the most intruders — including members of their own species. The white seems to advertise the sexual and fighting prowess as well as access to the best resources, and invites aggressive challenges from other birds.
Avian alphas tend to have the most white in their nests. These birds are in their prime, generally 7-12 years old. The older and younger birds build more ascetic nests, skipping the white decorations. Unlike young men in the human pickup artist community, the weaker birds refused to advertise unless they had the prowess to back it up. When scientists tried adding white plastic to their nests, the birds quickly removed it, not wanting to invite a fight.
Research published in Science