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It starts with a few falsetto yips, then blossoms into something resembling maniacal laughter, the yips stringing together into chattering howls. It's an attention-grabbing sound, and an eerie one: coyotes howling, usually in the evening or at night, a chorus that is being heard with increasing frequency throughout the Northeast—and not just in remote wilderness areas, but in towns, suburbs, and city fringes.

"Howling is a basic communication behavior in coyotes," says Gary San Julian, Penn State professor of wildlife resources. "It has several functions. One is to call the pack—really a family group—back together again after a period of individual hunting. A second reason that coyotes howl is to advertise their presence to other packs, essentially warning those other family groups against trespassing across territorial boundaries."

Coyotes have long been abundant in the West; San Julian has listened to their keening in Wyoming and Colorado. "I've also heard them more recently—while standing in my backyard in rural Centre County not far from Penn State."

Although archaeological evidence shows that coyotes lived in the East in past millennia, they were largely eliminated in the region following trapping and shooting by European settlers. But during the twentieth century, these predators have staged a remarkable comeback. Most wildlife scientists believe that western coyotes worked their way east to reoccupy the vacant habitat. Others suggest that coyotes remained present in wild areas of the East, refugia from which they expanded following a lessening of persecution by humans along with a population explosion of white-tailed deer, one of many foods that coyotes consume.

Today's eastern coyote is markedly larger than the western variety. Adult male eastern coyotes weigh 45 to 55 pounds on average (some are larger), and females weigh 35 to 40 pounds. Out west, most coyotes weigh 25 to 30 pounds.

Recent genetic studies indicate that the eastern coyote is part wolf. "The species concept in wild canines is fluid," San Julian says. "Different species can interbreed with other closely related species and produce fertile offspring. Generally, though, behavioral differences act to prevent such cross-breeding." Scientists theorize that as western coyotes moved east, they hooked up with lone wolves who, because of ongoing human persecution, were finding it difficult to locate mates from within their own kind. "Usually wolves will kill coyotes," says San Julian. But apparently some wolves, probably in Quebec and southern Ontario, added their genes and helped shape the eastern coyote.

"Coyotes are incredibly adaptable," San Julian reports. "They can switch from eating small mammals, including mice and voles, to dining on melons and apples and berries. They eat garbage. Some prey on domestic dogs and house cats. Coyotes are comfortable hunting on their own—catching small rodents in newly cut hayfields, for instance—and they also cooperate with each other to take larger prey, like deer."

The basic unit is a family group: an adult male and female, plus any grown offspring that have not yet dispersed into territories of their own. "Coyotes don't form large packs the way that wolves do," says San Julian. "A typical family group may number four of five individuals."

Coyotes have no problem coping with suburban sprawl; San Julian once watched a coyote pick its way across a six-lane highway in Illinois, among gas stations, big-box stores, and expensive houses. As coyotes live and forage around people and their dwellings, the canines may lose their fear of humans. In highly developed parts of southern California, coyotes have attacked humans in recent years. San Julian cautions people not to feed wildlife (other than birds), because that practice "can unnaturally habituate animals to humans."

Coyotes continue to be hunted and trapped in Pennsylvania, practices that keep them wild and wary. But despite the annual take—estimated at 20,000 in 2005—populations have grown, until now there are few areas in the state where coyotes are not found. It seems certain that more of us will be hearing those spine-tingling howls in years to come.

Gary San Julian, Ph.D., is professor of wildlife resources and an extension wildlife specialist in the College of Agriculture at Penn State. His email is jgs9@psu.edu.