Run-ins are on the rise between coyotes and city-dwelling humans, and scientists aren't sure why. Now researchers in Alberta think they've found a piece of the puzzle. Coyotes are more likely to creep into human spaces if they're unhealthy. Conflict between humans and coyotes has increased during the last 20 years, write University of Alberta graduate student Maureen Murray and her coauthors. Yet coyotes were expanding their range for decades before that. They've spread to inhabit nearly every part of North America. What makes some coyotes today march downtown and ride the light rail while others stay in a city's fringes and parks, never meeting a person? To explore the question, the researchers captured 21 wild coyotes in Edmonton, Alberta over the course of three years. They fitted the animals with GPS collars to track their movements. They also clipped a little hair from each animal's nape for chemical analysis. And they recorded every coyote's sex, age, and weight, as well as whether it looked mangy. Coyotes are susceptible to a type of mange caused by the mite Sarcoptes scabiei. Along with making their fur fall out, the itching causes coyotes to bite and chew their skin, which can lead to more infections. Mangy animals may also have trouble keeping warm. Eleven of the captured coyotes were healthy; ten had mange. During the study, four of the healthy coyotes were killed by cars. Meanwhile, six of the diseased coyotes died—four from exposure, and two from being euthanized after run-ins with humans. Two of the coyotes didn't send back enough GPS data for the researchers to use. From the rest of the collared animals, they detected a clear pattern: diseased coyotes roamed farther. They covered ranges that were nearly four times as big as a healthy coyote's home turf. They were more than five times as likely to come into developed areas, such as commercial or residential zones. And they wandered equally during day and night—unlike healthy coyotes, which are mainly nocturnal. By analyzing the carbon and nitrogen isotopes in the coyotes' hair clippings, the scientists could learn about their diets. The carbon signature of corn, which is packed into processed foods, showed the scientists that diseased coyotes were eating about a third more human food and trash than healthy coyotes were. (Another potential coyote food that bears the signature of corn: our pets.) Nitrogen analysis showed that diseased coyotes were also eating further down the food chain than healthy ones, consuming almost 90% less prey. A healthy coyote may never need to wander downtown. It spends its energy defending a small territory, maybe inside a city park, where it comes out at night to hunt and forage. But a sick coyote wanders widely and at all times of day. It looks for easy sources of food anywhere it can find them—like backyards and alleys. That means it's more likely to bump into a human along the way. Murray says the link between poor health and using human resources probably applies to coyotes in many places. Mangy animals may be especially desperate in a far northern city like Edmonton, though, because of the cold temperatures. "Our results can help mitigate human-coyote conflict by providing information about why coyotes use human resources," Murray says. If wildlife managers can prevent disease among coyotes, they might reduce the number of animals that come searching for human food. And keeping the streets clear of things a sick coyote might eat—compost, processed food waste, fallen fruit, and even spilled birdseed—could also prevent coyote run-ins. If urban centers are providing food and shelter for sick coyotes, helping infectious animals survive longer, and bringing them into contact with other coyotes, Murray thinks this could help explain why encounters between coyotes and humans are on the rise. Keeping these animals healthy and away from our trash heaps may mean that more coyotes live out a good life—that is, one where a human never sees them. This post has been edited to clarify that all of the coyotes in the study lived inside the city.
Image: by Oregon Department of Fish & Wildlife (via Flickr)
Murray, M., Edwards, M., Abercrombie, B., & St. Clair, C. (2015). Poor health is associated with use of anthropogenic resources in an urban carnivore Proceedings of the Royal Society B: Biological Sciences, 282 (1806), 20150009-20150009 DOI: 10.1098/rspb.2015.0009