Driving into Fairbanks on Saturday morning, Amy and were passing along the experimental agricultural fields managed by the University of Alaska. From the window of the car, Amy spotted a Coyote walking through the snow near a pond of melt-water. Though I’ve seen their tracks along the trails, and even through my property north of town, I hadn’t laid eyes on a live coyote in Alaska in at least a couple of years, which got me thinking about coyotes.
The species is a relative new-comer to the state, having arrived, according to the Alaska Department of Fish and Game, in the early years of the 20th century. They first appeared in Southeast Alaska before radiating northward into the interior over the next few decades. By 1940, coyotes reached a peak of abundance declining afterward to the more stable population that persists today across much of the state.
There are probably a number of reasons for the northward expansion, but most of them have to do with human impacts on the landscape. While the human footprint in Alaska is still, gratefully, relatively light, roads, agriculture, and human development are present. Coyotes, unlike their congeners the wolves, get along well, even thrive, around humans. Wolves do not, or rather humans have a tendency to kill off the wolves wherever we settle. And here is the rub: wolves kill coyotes. Researcher Laura Prugh in an interview with the Juneau Empire in 2010 said “Wolves are the major mortality factor, coyotes tend to live in the no-man’s-land between wolf packs.” They can and do co-exist, but wolves keep coyote numbers to a bear minimum in areas where the two species overlap.
Since their arrival, coyotes have become an important player in the northern ecosystem. They are generalist predators, meaning they eat a lot of different things. A 2010 paper about coyotes in the northern Alaska Range (just about 50 miles south of Fairbanks) found the most important food items in their diet were: snowshoe hares, voles, porcupines, carrion, and Dall’s sheep lambs. Of these, hares were by far the most important.
Interestingly they also found that coyotes were prey switchers, meaning they willingly select from whatever prey is most abundant, as opposed to generalists who switch only when forced. Prey-switching generalists, unlike specialist species, can play a moderating roll on prey populations.
Lynx, for example, are specialists. They forage almost exclusively on snowshoe hares and the populations of the two species are closely entwined. If the population of hares goes up, then a year or two later, so will Lynx. When there are too many Lynx, they force the population of hares down, causing a constant and predictable cycle of abundance. Coyotes however, eat whatever happens to be abundant which eases the pressure when populations of preferred prey is low. Pretty nifty right?
Coyotes of the northern Alaska Range favor hares, when hares declined, coyotes switched to voles, porcupines, and carrion. Despite the flexibility, so important are hares to their diet that when hare populations declined, it hurt coyotes too.
I thought the importance of porcupines in low hare years interesting. I mean, it’s not like a porcupine is easy to eat. Still, they are large (on average about 4x the size of a hare) so if a coyote can get one, it makes a substantial meal. But, the cost can be high, even fatal. In a reference to some unpublished data, one researcher found that at least two collared coyotes in the study area were killed due to ingested porcupine quills. Ouch.
Another paper related the abundance of hares not only to coyote populations, but also to Dall’s sheep. It’s one of those indirect ecosystem impacts that I find so darn cool. So when hares (the main food sources for our coyotes, as well as Golden Eagles) decline, those predators have to look elsewhere for food. In the Alaska Range, that means Dall’s sheep.
Over their multi-year study, the researchers found that when hare populations were high, it eased the predation pressure on sheep, but when low, those coyotes and Golden Eagles had to look up the mountains for food and it took a toll on the lambs.
I guess this finding is not particularly surprising, but it is a very clear demonstration of the way different elements of the ecosystem are very closely related. Though I doubt Dall’s sheep and snowshoe hares interact or compete in any way, the abundance of one can still have a very real impact on the survival of another.
The story of coyotes in Alaska is a fascinating one. These dogs were not even present in the state 115 years ago, but now, thanks to their uncanny ability to thrive where other predators cannot, they are a driving force in the ecosystem. I can’t help but like the coyote. Next time I see one, which will hopefully be soon, I’m going to stop, watch and admire those clever eyes until he slips out of sight. Invisible, I expect, is way coyotes prefer to be.
Papers used in this post:
Prugh, Laura. 2005. Coyote prey selection and community structure during a decline in food supply. Oikos. 110: 253-264.
Arthur, Stephen M., and Laura R. Prugh. 2010. Predator-mediated indirect effects of snowshoe hares on Dall’s sheep in Alaska. Journal of Wildlife Management. 74(8): 1709-1721.
