Roland Kays

The skull of a coywolf appears above. Coyotes are breeding with wolves, turning mice-eating coyotes into larger, hungrier animals.Roland Kays

New DNA evidence reveals that coyotes have bred with wolves in the the northeastern United States, turning mice-eating coyotes into much larger animals with a hunger for big prey, such as deer.

The resulting "coywolves" may, however, benefit ecosystems, since they appear to be filling niches once occupied by wolves that were eradicated by humans.

"We are finding repeatedly that hybridization is more common than we used to think," lead author Roland Kays told Discovery News.

"This is an evolutionary mechanism to generate new variation that can work faster than genetic mutation," added Kays, curator of mammals at the New York State Museum.

Kays and colleagues Abigail Curtis and Jeremy Kirchman took mitochondrial DNA samples from 686 eastern coyotes housed in museums, or obtained by donations from hunters, fur trappers and various government agencies. The scientists also measured 196 coyote skulls.

The study, outlined in the latest Royal Society Biology Letters, reveals that some of the largest specimens were indeed coyote and wolf hybrids.

Given where these animals came from and the degree of documented genetic diversity, the researchers can tell that a few coyote females mated with male wolves north of the Great Lakes.

Subsequent coywolf population expanded into western New York and western Pennsylvania, which also have populations of pure coyotes.

Coywolves aren't too hard to pick out from pure coyotes.

"They are larger, both in terms of body size and skull dimension," Kays explained. "Their skulls are especially wide compared with their length."

"Male coywolves are larger than females, while coyotes are not," he added. "Coywolves also tend to be more variable in terms of color, with red, dark and light morphs."

He said coywolves tend to hunt larger prey than coyotes do, scavenging or actively seeking deer, for example, which is possible given the coywolves' larger size.