Natalie Angier writes in the New York Times:
Perhaps no example of steroid doping so closely matches our own as that practiced by mother birds eager to give their offspring a wing up in the world. In the last few years, scientists have discovered that many female birds will fine-tune the dose of testosterone and other androgens they inject into eggs depending on a range of environmental cues.
According to Kristen J Navara, a biologist at the University of Georgia, female bluebirds mated to drab males deposit four or more times more testosterone into the yolk of developing eggs than do bluebirds paired with enviably cerulean males. Among black-headed gulls, said Ton Groothuis of the University of Groningen in the Netherlands, mothers supply the later-laid eggs in a clutch with significantly more testosterone than they donate to eggs they laid early on.
Whatever the species, the impact of the testosterone spiking is clear: chicks of either sex emerge from their shell beefier, more aggressive and more demanding of food than their peers from lower-T prenatal pools. Through hormonal enhancement, then, chicks sired by undesirable males can compete with the young of princes, and later-born chicks peck it out better with their older and bossier siblings.
Just imagine if there was an Olympics for bluebirds. But then, that’s what life is, no?