Urban coyotes are literally full of garbage -- and that's risky for humans, study suggests

CBC.ca
March 10, 2021

On slicing open the stomachs of urban coyotes, researcher Scott Sugden has pulled out food scraps that might have come straight out of a garbage or compost bin, including a fully wrapped burrito. One time, he even found a leather glove.

"I can understand a pineapple. I can understand a burrito. I can understand a doughnut. But a leather glove?" said Sugden, a research assistant at the University of Alberta in Edmonton. "There's no nutritional value whatsoever."

From Vancouver to Montreal, coyotes are increasingly being spotted in urban parks and neighbourhoods. And their junk food diet spells bad news for both the animals and the people they live alongside.

Coyotes that eat food discarded by humans tend to be unhealthy and may pose a health risk to humans since they carry more parasites and have gut bacteria linked to aggression, research by Sugden and University of Alberta colleagues found. Their study was published in the journal Scientific Reports last December.

There is also a greater risk of contact and conflict with humans as their poor health pushes them to seek out more food meant for human consumption instead of hunting rodents like mice and voles.

"Hunting an animal is work and requires energy, and so it's difficult for a coyote to do if it's unhealthy," Sugden said.

That makes the coyotes more reliant on human compost and garbage, which in turn makes them less healthy and perpetuates a vicious cycle, he said.

Some of the items found in the stomach of a single coyote in the University of Alberta study. Clockwise from the left: a leather glove, a Tim Hortons wrapper, small fruits including cherry pits and a grape stem scavenged from a yard or compost or garbage bin, an apple, a rodent's paw and some grass. (Scott Sugden/University of Alberta)
Keeping coyotes away from garbage is crucial
Coyotes have been in the spotlight in recent months amid reports of attacks on people and pets, raising questions over how city dwellers and their pets can live safely alongside the animals.

At least 15 people have been bitten or attacked by coyotes in Vancouver's Stanley Park in recent months, and conservation officers have warned that some have become aggressive and bold because they've been fed by humans. 

Sugden's research highlights the dangers of coyotes eating food meant for humans.

He examined nearly 100 urban and rural coyotes killed in the Edmonton area over the winters of 2017-2018 and 2018-2019 to see what they ate and how it affected their health. Coyotes don't chew their food and instead tend to rip them and swallow whole, making it easy to identify what was eaten, he says.

The fact a coyote would swallow a glove was clearly a sign of desperation, says Sugden.

"He was hungry, and he wanted something to fill his stomach," he said.

University of Alberta researcher Scott Sugden examines a coyote in a laboratory. He opened the stomachs of nearly 100 urban and rural coyotes to examine their diet and its impact on their health. (Scott Sugden/University of Alberta)
Sugden also looked beyond the contents of their stomachs -- which only records their last meal or two -- and looked at chemicals in the claws of the animals for insight on their diet.

The type of carbon and nitrogen found in the tissues is linked to diet. Higher levels of nitrogen-15 are linked to eating more protein, while higher levels of carbon-13 are often tied to consuming processed human foods containing corn-based ingredients such as high fructose corn syrup, cornstarch and maltodextrose.

Junk food diet linked to deadly parasites
Sugden's analysis suggested urban coyotes ate 2.5 times more human food than rural coyotes, and 25 per cent less prey -- consistent with the finding that there were fewer mice, voles, and chunks of deer in the stomachs of urban coyotes compared to those of rural coyotes.

There were also signs that the urban coyotes were in poorer health compared to their rural counterparts:

• They had much less fat in their kidneys, suggesting they weren't as well nourished.
• They had 37 per cent larger spleens for their size, suggesting they had more challenges to their immune system.
• They were 50 per cent more likely to carry the parasitic tapeworm E. multilocularis, which can cause a potentially deadly illness when transmitted to humans.

Dr. Emily Jenkins, professor and acting head of the Department of Veterinary Microbiology at the University of Saskatchewan in Saskatoon, has been researching the parasite for quite some time but was not involved in Sugden's study.

"The irony is it actually has almost zero impact on coyotes' health, but it has significant impacts for human health and for dogs," she said.

If a dog or human accidentally eats the tapeworm eggs found in the feces of an infected coyote -- something that's relatively rare -- the larvae form cysts in the liver.

"It basically behaves like a parasitic tumour and can spread and even be fatal without immediate and aggressive treatment," she said.

Jenkins says while the parasite is rare, there has been an increase in reported cases in western Canada and southern Ontario -- and the risk is enough to keep her from allowing her own dog off leash in either her own city of Saskatoon or in Edmonton, where she grew up.

The parasite tends to affect younger animals, and the younger age of the urban coyotes in the study might help explain why they had more parasites, she said.

On the other hand, she said the larger spleen suggested the urban coyotes might have more infections with other pathogens that the researchers didn't look for.

Gut link to aggression?
For Sugden, the most interesting bit was the impact an unnatural diet had on the microbes that live in the gut of the coyotes.

In humans, those microbes, known as the gut microbiome, have been found to have an impact on health, behaviour and the immune system, and the same is true for animals, Sugden said.

He found that coyotes that ate more human food had more gut bacteria similar to those in humans than those that hunted more prey.

"For coyotes, this was bad news because this was correlated with other aspects of poor health," he said.

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There's also some evidence it could be linked to more aggression by the animals.

Fusobacteria in the gut are linked to protein-rich diets and lower aggression in dogs, Sugden said. And one urban coyote in the study that killed a large domestic dog had no Fusobacteria in its gut at all.

"If we feel that eating human food has the potential to affect behaviour, [then we need] to address the root," he said. "Then we reduce the likelihood of conflict. We reduce the likelihood of parasite transmission."

For this Alberta woman, the good news was she had contracted a rare, deadly parasite
Jenkins cautions against reading too much into links between different facets of the study since none were shown to cause each other. For example, the aggressive coyote mentioned in the paper may have been infected with a disease unrelated to its microbiome, she said.

However, she agreed that keeping coyotes away from human food is key to reducing risks to humans.

Are you feeding coyotes inadvertently?
Many cities, such as Calgary, Toronto and Vancouver, already ban residents from feeding wildlife and threaten violators with fines. Edmonton is considering such a bylaw.

Securing compost and garbage bins to prevent inadvertent feeding is also important, says Sugden.

The wildlife conservation group Coyote Watch Canada also recommends that people:

• Keep pet food and water bowls indoors
• Pick ripe fruit and remove rotten fruit from the ground
• Avoid having large amounts of bird seed on lawns as they can attract prey such as birds and rodents.

Sugden said excluding coyotes from cities isn't practical, but the animals can be encouraged to remain in natural urban areas such as river valleys and hunt their regular prey.

Jenkins agreed that making human neighbourhoods less appealing for coyotes and controlling access to garbage is the most effective long-term solution. She said culling coyotes tends not to work, as the habitat "will refill almost immediately with new, needy, desperate young coyotes with exactly the same risk factors" such as tapeworm infections.

"We've got lots to learn about the wildlife and what that means for our health as well," she said.