bright-beaked birds get all the chicks

In the animal kingdom, females usually prefer to mate with the most elaborately ornamented males — the peacock with the showiest tail or the songbird with the most complex song. It’s long been speculated that these showy sexual displays give honest information about the male’s vitality – only the healthiest males could afford such extravagances – and now a pair of studies in the April 4 Science give direct evidence that this is indeed the case. Reseachers from the University of Glasgow focused on beak color in male zebra finches, while a team from the University of Bourgogne in France studied beak color in male blackbirds. Birds with very bright orange beaks were found to have very high levels of carotenoids, a nutrient that boosts the immune system (and that makes carrots — and bird beaks — orange). Birds with stressed immune systems had dull-colored beaks because disease drained the color-giving carotenoids. Males with the brightest-colored beaks – the ones with the most robust immune systems — were the most sexually attractive to the females, and the drab-beaked males were ignored. “This result shows that sexual advertisement honestly signals health,” write the authors of the French study. Left unexplained is why all vertebrates — birds included — find Carrot Top so unappealing.

This news brief appeared in the Random Data column of the Boston Globe’s Health/Science section on 4/15/2003.