Certain coyotes are known to have frequent unnerving encounters with humans and their pets in residential neighbourhoods, and scientists now have an explanation.
It turns out that coyotes infected with a common skin parasite tend to develop habits that make them problem animals.
"These coyotes that were losing their hair and were sick were more likely to run into people in residential areas, especially during the day," says Maureen Murray, lead author of a new study on urban coyotes published today in Proceedings of the Royal Society B.
Coyote sightings and encounters have been increasing in cities across Canada, from Vancouver to Toronto to Newfoundland.
Murray is part of a University of Alberta research group that has been tracking coyote sightings in Edmonton since 2000.
"And it's been increasing exponentially every year," she says.
While coyotes rarely attack pets or humans, their growing presence in cities makes many of their human neighbours uncomfortable.
"It comes down to this unease about a carnivore and a predator around people's backyards, around people's kids and their pets," Murray says.
Most urban coyotes hide in ravines and golf courses, away from humans, eat mainly small animals that they hunt, and are more active at night than during the day.
Murray wanted to find out why certain coyotes seemed to be spotted unusually often on city streets during the day — was that linked to their age, sex, or something else?
Diet leaves traces in hair
Murray and her collaborators caught 19 coyotes in Edmonton and put GPS collars on them to track their location every three hours over an average of four months. They took note of the animals' age, sex and whether they had any signs of sarcoptic mange, a common parasitic mite that lives in the skin, causing itching and hair loss. They also took hair samples to find out what the animals had been eating.
Different kinds of food leave different chemical signatures in hair or fur. Animals with diets higher in meat tend to have higher levels of nitrogen-15, a heavier form of the element nitrogen. Animals who consume more processed human food — which contains corn-based ingredients such as corn starch and corn syrup — tend to accumulate more carbon-13, a heavier form of the element carbon.
The researchers found that eight of the 19 coyotes showed signs of mild mange, mainly in the form of red patches on their hind legs. The coyotes who were sick had four habits that tended to bring them in contact with humans:
- A greater likelihood of spending time in developed residential or commercial areas of cities.
- Wandering over much bigger ranges.
- More active during the day.
- Eating of more human food and less protein, determined by hair analysis.
The researchers aren't sure why the sick coyotes showed these behaviours, but it may be that sick coyotes rely on easily accessible food from humans such as compost scraps and the shelter provided by human structures such as porches. They could be more active during the day because they find it too cold at night without a full coat of fur.
Many sick animals died
Sadly, many of the sick coyotes got sicker over the course of the study.
"Some of the animals in our study ended up with almost no hair at all," Murray says.
Six of them died. Murray says four of them had apparently frozen to death in their sleep without their hair to protect them from Edmonton's frigid winter temperatures. Two others were euthanized by city officials because they refused to leave the backyards where they had taken shelter.
Murray says that knowing why the animals were spending time among humans may help city officials figure out how to manage problem coyotes.
While cities are generally reluctant to intervene when animals are sick, she says, her results suggest that "that letting nature sort of run its course for these coyotes in cities might not be the best course of action for people."
Coyote mange can be transmitted to dogs, something that Murray says people who have pets in areas with coyotes should be aware of.
However, the disease can be treated with an ointment.
Murray recommends that people discourage coyotes from living near them by eliminating possible food sources. Securing compost and green bins, and cleaning up spilled bird seed and rotting fruit that has fallen off trees in their yard may help.
She hopes that knowing why coyotes might be seeking shelter in their backyards will encourage people to take action.
"I feel like those sorts of messages can resonate with people a lot more if you know why something might work."