Squawking for Sex

Like rival men in a singles bar vying to attract the most beautiful woman, the males of a tropical shorebird called the bronze-winged jacana spend much of their time competing for female attention. But single men would be wise not to adopt this bird's tactics: According to a study in the current Animal Behavior, male jacanas lure females into love-making by yelling at them as hard as they can.

Compared to many other female birds, female bronze-winged jacanas have lucked out in the evolutionary sweepstakes. Instead of mating to only one male, who then guards her like an overly jealous husband to ward off rivals, females maintain small harems of males who vie for their favors and take care of their young, says behavioral ecologist Stuart Butchart of the University of Cambridge in England. Butchart and his colleagues wondered how important the male's excessive yelling was to get female attention.

To find out, the scientists tracked bronze-winged jacanas during three successive breeding seasons at their home among floating lotus plants on a freshwater lake in southern India. After netting birds, banding their legs to identify individuals, and releasing them, the researchers sat back with telescopes and tape recorders to watch and listen. Male jacanas stepped up their yelling when a female was visiting the territory of a rival male in the harem, when their mate was further away, and during the day or so just before she laid her eggs--the period when the eggs are fertilized. To make sure it was the yell and not something else that enchanted the females, the team set loudspeakers on floating platforms and played back the yells. Females flew quickly to the speakers broadcasting the yells of one of their cuckolds, but ignored recorded calls of doves. In addition, Butchart says, "the males that yelled at the highest rate gained the most copulations."

"This study shows a unique and interesting adaptation that hasn't been seen in other species," says behavioral ecologist Mike Webster of the State University of New York, Buffalo. But it's not clear yet why females seek out the noisiest males, says behavioral ecologist Robert Montgomerie of Queens University in Kingston, Canada. Perhaps yelling behavior is a measure of fitness, he suspects. "If you can yell loud and long, it may be a sign of health."