Female birds nest together
When birds lay more eggs than normal, it is usually a sign that something dramatic is happening to the flock. While investigating that phenomenon among Western seagulls on a California island, two researchers made a startling discovery: most of the apparent egg overproduction was the result of homosexual pairings of female birds, each producing the normal number of eggs. The female pairs—some 10% of the population—produce both sterile eggs and eggs fertilized by a visiting male. "We were absolutely astounded," said George Hunt, 35, a biologist at the University of California at Irvine. "This sort of thing has not been found before and was clearly not what we anticipated."
Hunt and his wife Molly, 32, who is also his co-researcher, studied 1,200 pairs of the gulls for five years on Santa Barbara Island, an uninhabited rock about 40 miles from Los Angeles. Seven of eight female pairs that were trapped and marked by the researchers in 1975 were still together in 1976. In all of these pairs, one of the females adopted some male courtship and territorial behavior. In three cases, a female attempted to mount and copulate with her female mate.
The Hunts are not sure why the phenomenon arose and, with other researchers, are currently examining gull hormones for a possible answer. But the likely explanation is simply a shortage of males. If a female cannot attract a permanent mate, but can manage to become impregnated by a mated male, it makes sense to move in with another female who can share duties of protecting and feeding the young. Such behavior, says George Hunt, "would increase the probabilities of raising the young from zero to about 10%." So far the Hunts have "tentative, preliminary evidence" of a male shortage among the birds, but not enough to explain why Western gulls are the only known wild birds to produce homosexual nesters. ∎