HHow Compost Piles Are Creating Problem Coyotes

We think we're being environmentally friendly by composting, but without the proper precautions, those piles can be problematic for wildlife. Learn what one study discovered about the surprising impact compost piles have on urban coyotes.

By Jaymi Heimbuch

 

Coyotes live in practically every city in the United States, yet the vast majority of human residents never spot a single one. That’s because urban coyotes are skilled at steering well clear of humans, even switching to nocturnal behavior just to stay out of sight.

So what makes some coyotes more likely to be active during the day, or hang around in areas closer to humans with a higher chance of having a run-in? Are these animals simply more bold and brazen, destined to become problem animals — or is there more to it?

We were really interested in the question of why certain individuals are much more likely to be encountering people when really most [urban] coyotes avoid people, tend to stick with natural areas, tend to be quite nocturnal. We wanted to know why there are these big differences in behavior across coyotes.

Maureen Murray

A study published earlier this spring in Proceedings of the Royal Society B helps answer this core question about urban coyotes. Maureen Murray of the Edmonton Urban Coyote Project and her team caught and collared 19 coyotes. Using GPS location data from the collars, hair samples collected while collaring, and video footage placed around nine compost piles, the researchers discovered that these very compost piles and a common disease called sarcoptic mange are two key factors in causing coyotes to alter their behavior and potentially be involved in more human-coyote conflicts.

When the team collared the coyotes, they noted their general health including whether or not they had signs of mange. As they collected GPS collar location data, they noticed distinct differences. The individuals with mange had not just slightly different behavior, but distinctly different behaviors and habits than those individuals without the disease.

Mange is a highly contagious skin disease caused by a mite. It is commonly found in animal species, including our own domestic dogs. The mites burrow just under the skin, causing extreme itching and discomfort as well as hair loss. Imagine the feeling of a constant, pervasive itch and a desperate need to scratch, to the point that you injure your own skin and have trouble concentrating on anything else including eating. Imagine also that the itch causes your hair to fall out, leaving you vulnerable to the cold. That is what an animal with mange is experiencing. So it is no surprise that those individuals with mange would have different behaviors. But the extent to which it affects them is of interest.

“The guys with mange had these huge home ranges, like 60 square kilometers,” says Murray. On the other hand, “the healthy ones never really leave the natural areas. As our sample got bigger and bigger, this pattern kept holding that the ones with mange weren’t nocturnal like the healthy guys. They were active pretty equally at all times of day, they used residential developed areas five times more often, and they had four times larger home ranges.” In other words, the coyotes with mange travel much more, in areas and at times of days where they are much more likely to encounter people. But that isn’t the only important distinction.

The coyotes with mange also tended to use residential back yards, specifically those with compost piles. The lure of the compost pile is a key piece of the puzzle in behavior differences among coyotes, but the reasons why are complex.

The team wanted to discover if the compost piles aggregate coyotes, attracting sick coyotes and healthy coyotes alike, and perhaps assisting in the spread of mange among these urban animals. To find out the answer, the team put cameras on the compost piles and looked at how often a coyote with hair loss — a sure sign of mange — appeared and how far apart the visits of individual coyotes were spaced.

With the help of the remote cameras, Murray found that coyotes with hair loss were recorded at compost piles more frequently than they were recorded on cameras set up in natural areas. Not only that, but the visits to compost piles by different coyotes were much closer together in time, increasing the chances of healthy coyotes coming into contact with disease.

Coyotes are naturally territorial so healthy coyotes hunting for rodents and small prey in their home range are sure to let visiting coyotes know they aren’t very welcome on their turf. In normal wild situations, the chances of many coyotes meeting up often enough to spread mange are much, much lower. But when you throw in a steady supply of food provided by humans, the dynamics shift. In short, the compost piles are bringing coyotes together far more frequently than happens in natural areas, and more of those coyotes are sick.

The team found that the difference between healthy and sick coyotes isn’t just in where they roam and when. It also comes down to the specific foods they’re eating and how their diet is affecting their overall health.

An urban coyote eats bread left near a walking trail
Coyotes are opportunistic eaters, and leaving any food out - whether that is fallen fruit from a backyard tree, pet food on the porch, or uncovered compost piles - is a sure way to attract them to your home. © Jaymi Heimbuch / Urban Coyote Initiative

Murray wanted to find out if there is something about eating from these piles that causes the coyotes to get sick beyond just contact with other coyotes. In other words, is the food itself perhaps to blame in compromising a coyote’s immune system?

“When we ended up looking at the stable isotope signatures of their hair, we found that the sick coyotes assimilated a lot less protein than the healthy guys. If a sick coyote has a worse diet, it’s hard to picture them sort of breaking out of that cycle [of illness] since this lower protein diet is also bad for their health.”

Next, the team took samples of the compost at the different piles to test for fungal toxins called mycotoxins.

Mycotoxins can contaminate food supplies from livestock feed to grains that go into human foods. In animals and humans who have consumed mycotoxins, the effect can range from vomiting and weight loss to immune suppression and, in the worst cases, organ failure or even cancer. Immune suppression was of interest to Murray, as this could be part of the reason why coyotes feeding from compost piles tend to be sick. Even if they arrived sick, the food they consume could be making it harder to fight off that illness.

The team found that mycotoxins were present in a significant number of the compost piles, and some piles had disconcertingly high concentrations. “It was quite shocking that an animal eating at this compost pile, you wouldn’t be able to legally give that food to a pet or to livestock,” says Murray.

Piles of food waste we don’t normally think about, or think of as being environmentally friendly, could have negative affects for coyotes, and also for a lot of other wildlife like bears or raccoons or foxes.

Maureen Murray

Easily accessible sources of food change the behavior of wildlife, bringing animals in contact with each other more frequently than would naturally happen. This aids in the spread of many other diseases besides mange as well. In the case of compost piles specifically, it also aids in the spread of toxins that could have even deeper health consequences.

Now the team’s questions take on a chicken-or-egg shape. Are the coyotes visiting the compost piles because the piles are an easy source of food, one that is needed as the mangy coyotes struggle to hunt natural food sources? Or are the coyotes taking advantage of pockets of food that ultimately weaken their immune systems and make them susceptible to contracting mange via other visitors to the same food source? This is an area of future study for Murray.

Either way, the team has been able to point to compost piles as a problematic issue for the health of coyotes. The piles play a role in reducing the health of urban coyotes, bringing sick coyotes into residential areas, and increasing the possibility that coyotes come into conflicts with humans.

Making compost piles difficult for wildlife to access is a simple way to reduce the temptation for coyotes to come near a residential dwelling. Keeping coyotes away from human food sources protects them both from disease and from the potential of becoming a problem animal. Thus, putting a lid on compost piles is both a proactive and a compassionate solution.

In fact, urban wildlife managers universally recommend removing any and all food and water sources around the home as a way to keep wildlife out of residential areas. The less food is in a yard — from bird seed scattered on the ground under a feeder, to ripe fruit fallen under trees, to lids left off of trash cans or barbeque grills left coated in grease — the less likely it is that wild animals become habituated to humans and turn into problem individuals, perhaps problematic enough to be lethally removed.

A lot of coyote management is focused right now on to remove or not to remove because it’s pretty hard to get a real problem animal to change its behavior. Managers are stuck between a rock and a hard place; some residents are really concerned about the presence of coyotes, but a lot of residents are super excited about the presence of coyotes and don’t want to see them harmed or relocated. We’re hoping our results help the city better target how to prevent conflict. We don’t mean to imply that all conflict all the time is related to disease, but it does shed some light on a different approach we could be taking.

Going after easier food sources such as those found in backyards, taking up shelter in residential areas like under houses and decks, and traveling during the day and in more heavily populated areas are all actions with the potential to cause conflicts. Murray’s research is helping to uncover specific causes for this kind of “unnatural” behavior among urban coyotes. Now that the team has made the connection between compost piles and the health of urban coyotes, they can look more deeply into how residents can take proactive steps to avoid creating problem coyotes. This is the kind of research that goes a long way in promoting coexistence through science.

“It’s very rewarding to be able to collect knowledge about coyotes and then teach people there’s a reason why conflicts are happening and that we can do a lot to prevent those, rather than [conflict] being an inevitable consequence of living with wildlife.”