BLOOMINGTON, INDIANA--Every fall, hunters in the Jackson Hole, Wyoming, area bedeck the countryside with hundreds of steaming piles of elk guts. This gruesome scene is a bonanza for the local population of ravens, which has exploded in recent years as hunting has increased, a researcher told the Animal Behavior Society meeting here on 15 July. If not contained, the ravens could threaten Jackson Hole's biodiversity.
Normally, fall is the leanest time of the year for the ravens; many fledglings don't make it through their first fall when food becomes scarce. But with elk guts to supplement their diet, more birds should be able to survive.
To determine if the surge in the number of ravens was related to the fall elk hunt, biologist Crow White of the University of Montana monitored gut piles. He found that the number of ravens increased exponentially with the number of piles. In areas with no piles, about two ravens show up per square kilometer. When one gut pile is present, that number goes up to 14, and two piles attract an average of 87 ravens per square kilometer. "It turns into a raven circus," says White. During the fall hunt, there are around 3.5 piles per square kilometer. The guts seem the only explanation for the raven rise since neighboring Teton Valley, alike in every way except for the elk hunt, hasn't experienced a boom.
While the feast is good news for young ravens, it is potentially bad news for other bird species whose eggs are another raven favorite. "Ravens in some cases are major predators on other bird species, particularly those that nest in communities," says biologist William Boarman of the U.S. Geological Survey in San Diego. In Jackson Hole, local songbirds, waterfowl, game birds, and possibly red-tailed hawks could suffer.
White believes there may be ways to slow the ravens down. Covering the guts with sticks or dirt or spreading them out could deter ravens because they are wary when food has been disturbed. White is planning to test this idea in the fall.