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Birds of a Feather Woo Together

Peacocks that put on dazzling mating shows prefer to strut their stuff with close relatives, according to a study in tomorrow's Nature. The affinity between brothers is so tight, in fact, that they can somehow recognize each other even after being separated before hatching. Although researchers don't yet know how the peacocks achieve this reunion, the birds might be attracted to family sounds or smells.

Peacocks and some other species of birds lure females by putting on a Mr. Universe-esque show of their collective machismo. When they join forces to call, flaunt their plumes, or dance together, titillated females flock to the stomping ground, called a lek. Often, just a few studs mate with most of the female fans--and yet males without a hope of mating still show up to strut their stuff. Researchers predicted years ago that leks composed of close relatives might explain this conundrum: By helping their more attractive brothers win mates, males can vicariously pass along to the next generation some of their shared genetic heritage.

Behavioral ecologist Marion Petrie of the University of Newcastle, United Kingdom, and colleagues from the University of Sheffield, UK, have followed the soap opera of matings and lekking patterns of about 200 peafowl in Whipsnade Park, some 30 miles north of London. During one experiment, the researchers isolated eight peacocks with four peahens apiece and removed all the eggs that were laid. The researchers incubated the eggs, raised all the young together, then reintroduced the peafowl to the park--a few at a time in different batches. Three years later, 19 peacocks had established display territories in the park. When Petrie mapped these territories, she was astonished to discover that many brothers and half brothers lekked together, hanging out as close as 2 meters apart. Throughout the entire park, related males were separated by 117 meters, on average, while unrelated males kept a distance of 183 meters.

"It's extraordinary that [the brothers] found each other," says Petrie, considering that they were raised in a brood of related and nonrelated birds. The young birds might clue in to an odor or some aspect of their call that is genetically influenced and shared by their siblings, says behavioral ecologist Paul Sherman of Cornell University in Ithaca, New York. The next step, he says, is to identify these characteristics by modifying them in young birds to see whether the birds later seek out unrelated, yet superficially similar peers.