Consider yourself to be a grey fox. You’re about the size of a housecat, and you rely on mice and other rodents to keep your stomach full. However, this puts you in direct conflict with coyotes, who do not only want your supper but are also willing to knock you off.
So, where do you seek refuge? Perhaps a black bear’s territory.
According to a study published this week in the journal Oecologia, black bears play a significant role in regulating competition amongst all types of smaller predators in the Nevada highlands.
“Many carnivore species are disappearing, but black bears and coyotes are exceptions,” says Remington Moll, a wildlife scientist at the University of New Hampshire and the study’s primary author. “They’re both generalists, as we call them. They consume a wide variety of foods and prey, so you’d think these species would compete, but there have been little studies on them.”
Gray foxes and black bears compete with coyotes because they are such versatile eaters. Coyotes and bears, for example, also scavenge carcasses, but the much larger black bears are likely to drive away anybody else who attempts to get a bite. This frees up space for the grey fox, which is considerably smaller.
This is part of a broader body of work called “landscapes of fear”: Ecologists have discovered that the methods that prey species escape predators alter whole ecosystems, from the plants to the soil itself, from Yellowstone to Great Barrier Reef lagoons.
The study is part of a wider endeavor to count and map western Nevada’s black bear population. According to Moll, this area used to have a black bear population that dwelt in the high mountain pine woods. “Black bears were almost extinct a few decades ago. The bear population in California, on the other hand, has been thriving exceptionally well, and those bears are repopulating the Nevada site.”
The crew had already collared a group of bears with GPS trackers as part of that investigation and was able to figure out the animals’ home areas. It was more difficult to track the movements of shy foxes. The crew built up a trail camera network that takes pictures whenever an animal passes by. They baited the animals with a mix of raspberry extract, anise extract, fish oil, and “Ultimate Bear Lure,” an attractant that hunting stores describe as created from “all-natural secretions,” to persuade them to explore the cameras while they were in the vicinity.
The fact that black bears hibernate creates a natural experiment: the bears take over the landscape for half of the year. Then, in the autumn, they effectively vanish.
When bears are present, the cameras discovered that foxes spend substantially more time inside the core bear area. There were no coyotes to be found. With the bears gone for the winter, the coyotes advance into bear territory, scattering the foxes. With the shifting seasons, Moll says he’s not sure why the coyotes migrate to the momentarily unoccupied bear habitat. “It appears that there is something about the food availability; perhaps some areas are better for winter survival.”
There are some limitations to the findings: Because the study is only a correlation, the researchers can’t determine for sure why foxes and coyotes migrate from place to place. They also have little idea how foxes and bears interact when they share space, such as if they keep far apart or are at ease with one another. (This would need GPS collars on both animals, according to Moll.)
Nonetheless, Moll is taken aback by how strongly the foxes seem to select bear territory. “It had a bigger impact than environmental factors like snow, and it had a bigger impact than the amount of prey available.