Unlekky in love

 作者:佟泶     |      日期:2019-02-27 02:09:00
By Adrian Barnett MALE black grouse are famous for staging flamboyant courtship dramas en masse—unless they live in parts of Sweden, that is. Swedish biologists have found that a grouse’s life can be much more solitary, and they say this shows that the birds’ mating behaviour is far more open to outside influences than had been believed. Black grouse, Tetrao tetrix, are a “lekking” species. The males gather annually for courtship displays at traditional lek sites where they jump up and down, and call frantically. The females choose a mate from the posturing crowd. But Jacob Höglund and Sabine Stöhr of Uppsala University report in the current issue of Journal of Avian Biology (vol 28, p 184) that they have found an area, some 30 kilometres northwest of Uppsala, where the black grouse do not gather. “We could hear them clearly, but there were no leks to be found,” says Höglund. When they tracked down the males, the birds were found to be calling alone. Höglund says that lekking occurred in the area around 20 years ago so the transition to non-lekking must have occurred quite recently. He suspects that the change in behaviour is related to their habitat. “Black grouse leks occur in open spaces, normally in marshy patches within the forest,” he explains. “Here the females can see the males, and both can watch out for goshawks, their major predator.” But in the last two decades, foresters have drained the marshes and allowed birches to colonise former lekking sites. “Other changes have included the mix of trees, altering the quality of the forage available to the needle, berry and bud-feeding bird,” says Höglund. “This has lowered the density of the birds to a point where lekking is not a viable strategy.” Höglund adds that these observations may change scientists’ views of how much mating patterns in birds can change. “Black grouse are invariably reported as a species that can breed in no other way other than by lekking,” he says. “Our data show that this is clearly not the case.” He claims that this is “incontrovertible evidence” that birds’ mating behaviour is not genetically fixed, and can adapt to environmental changes. “My concern is that the changes in behaviour Höglund describes may indicate populations on their way to local extinction,” says Bill Sutherland of the University of East Anglia. He says that biologists have started to observe the same effect in Britain,