Apr. 10, 2003 Ah, spring, and the male grouse's instincts turn to the lek.
He will congregate with several of his fellows in an area called a lek where all will make courtship displays in the hope of attracting the attention of females. With luck, he'll be one of the few selected for mating and will have the opportunity to father part of the next generation of grouse.
"The nearest human equivalent (to a lek) would be a singles bar," said Robert Gibson, a behavioral ecologist and a professor of biological sciences at the University of Nebraska-Lincoln, who has studied the lekking behavior of birds at Nebraska's Valentine National Wildlife Refuge and other sites around the world.
While Gibson acknowledges the significant role of mate selection in lek formation, he said he's convinced there's more going on than just that.
"Females, when they're ready to breed, might visit one lek or several leks. They'll check out a number of males and eventually they'll select a male to mate with," Gibson said. "It turns out they all usually choose the same guy, or a very small subset of the guys gets chosen. What you have is a group of males who are apparently doing something together, but only a few of them are getting anything for it that one can see in terms of reproductive success. How do you explain all the guys who are there who apparently are not mating?"
Gibson said he thinks that at least in the case of greater prairie chickens, a species of grouse, males are often looking for more than the opportunity to pass their genes on to the next generation--they're also trying keep them alive in this one by joining a group to evade predators.
Grouping to avoid predation is common in the animal world. Moreover, in many animals, conspicuous courtship displays attract predators as well as mates. Thus it seems likely that males might join leks to avoid predation. This idea was first floated by the late British ornithologist David Lack in the 1960s, but the suggestion was widely ignored because other scientists rarely observed incidents of predation in leks. "This idea's been in the trash, really, the last 20 years," Gibson said. (more)
Gibson was familiar with Lack's hypothesis, however, and he and his research team found evidence to support it when they spent six weeks studying two closely related grouse species, greater prairie chickens and sharp-tailed grouse, at the Valentine National Wildlife Refuge.
"We'd go out every morning, stop at the leks and spend all morning watching them to see what the birds were doing," Gibson said. "We watched some sharp-tail leks, we watched some prairie chicken leks, and we watched some mixed leks. And one of the things we noticed right away was that we would see male greater prairie chickens visiting sharp-tail grouse leks and we didn't see the opposite."
Now, if a male's chances of mating are already small when he joins a lek of his species, it stands to reason that his chances probably are not improved if he joins a lek of another species. In fact, the researchers found that displaying with sharp-tails did not increase a male prairie chicken's opportunities to court prairie chicken females.
To Gibson, that was a good indication that something other than just mate selection was going on. Since he also found that prairie chickens displayed more and were less vigilant than sharp-tails, if they join sharp-tail leks and sharp-tails don't join theirs, that other factor might well be predator avoidance. A few weeks of observation wouldn't make the case, though, Gibson said. It would take years of observation to acquire the necessary data. Fortunately, someone had already compiled it.
Leonard McDaniel, a now-retired biologist with the U.S. Fish and Wildlife Service in Valentine, had gone around the refuge every spring for several years locating and counting all the 20 to 30 leks for each species. McDaniel generously shared his data with Gibson and his team, allowing them to perform a statistical analysis of the data. That analysis confirmed that prairie chickens did join sharp-tail leks, but not vice versa.
"That finding suggests that male prairie chickens benefit from lekking with sharp-tails, which in turn implicates predation," Gibson said.
In other words, a male prairie chicken in a sharp-tail lek isn't necessarily looking for love in all the wrong places. He may just be trying to survive.
The results of the study by Gibson and his team were published in the Proceedings of the Royal Society, Biological Sciences, in December.
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