WILLIAMSBURG, VIRGINIA—Throw a coyote a bone, and you may just change the shape of its skull. Research presented here this week at the 47th Annual Meeting of the Animal Behavior Society reveals that when these canines chew on hard objects as pups, bones in their skulls become shorter and thicker, allowing them to eat a wider variety of food as adults. The researchers say this is the first time food has been shown to have such a dramatic impact on the anatomy of any animal.
Coyotes (Canis latrans) are one of the most successful large carnivores in North America. In recent years, they have expanded their range from the rural American West to urban areas such as Chicago and Washington, D.C. Underlying this success is a coyote's unusual ability to adapt its diet to local conditions. A Coyote can kill and eat an elk 10 times its size and survive on garbage scraps in urban areas.
To figure out what makes the animals so adaptable, ethologist Suzanne LaCroix of Michigan State University in East Lansing and colleagues studied a group of coyotes being raised in captivity at a U.S. Department of Agriculture field station in Utah. Shortly after the animals were weaned, the researchers randomly split eight brother pairs into two groups: one frequently received sheep and cow femurs to gnaw on, and one dined exclusively on a soft diet similar to canned dog food. When the coyotes were 18 months old, a year after they reached adulthood, LaCroix's team compared the two groups' abilities to scarf down rawhide chew treats and beef shank.
The bone-chewing coyotes consumed their rawhide treats more than three times as fast and ate nearly 1.5 times as much of the beef shank as did coyotes without access to bones as pups, LaCroix reported at the meeting. The beef shank also looked different after it had been chewed by the two groups. The bone-chewing coyotes stripped off all of the baked muscle and removed the bony ends of the shank, but the nonbone-chewing group was unable to remove any of the bony ends. Removing the ends of bones gives coyotes access to the nutrient-rich marrow, LaCroix said.
These improvements in bone-chewing ability were not due to experience and skill alone. Instead, the researchers found that regular access to bones altered the musculature and bone structure of the coyote skull. When compared with coyotes that consumed a soft diet, the coyotes that chewed on bones had significantly shorter and wider mouth bones as adults. These coyotes also sported bigger chewing muscles and a more prominent sagittal crest, the ridge of bone at the top of the skull to which these muscles attach. That allows them to bit down harder on their food, LaCroix said.
Behavioral ecologist Stan Gehrt of Ohio State University in Columbus says LaCroix's research sheds light on a question that has plagued ecologists for years: With so many different kinds of food to chose from, how do coyotes decide what to eat? The study should also serve as a warning to urban wildlife managers, he says. Coyotes that feed on human garbage, which is typically soft, will become dependent on this food, as they won't develop the skulls needed to kill other animals. That will "constrain them to have to take more advantage of human-related foods, which could increase conflicts with humans."