June 8, 2000
Seeley Swan Pathfinder
Seeley Lake, Montana
by Mike Thompson
Montana Fish, Wildlife & Parks
Game Range Columnist for the Pathfinder
As I'm reviewing the results of Jamie Jonkel's annual carcass count on the Blackfoot-Clearwater Game Range, it occurs to me that the Roadrunner and Wiley Coyote cartoons I loved to watch as a kid were not so far from reality.
No, I don't mean that Jamie found any remains of misfired Acme-brand "Roadrunner Getters" on the Game Range. Or any fresh holes through trees or boulders in the shape of a spread-eagle coyote.
I just mean that predators often work harder for their prey than we sometimes realize.
This is the fourth consecutive year that Jamie and a fairly substantial volunteer army have counted dead elk, deer and other wildlife on the Game Range in early spring. The idea is to document trends in winter deaths from starvation, disease, predation, old age or bad luck.
And, in the 5-square-mile area where most of 856 elk and numerous mule deer and white-tailed deer were concentrated from December through April, only 28 elk and deer carcasses were found on April 29 and 30.
It's not that Wiley Coyote never wins. Jamie's wildlife coroners were able to attribute 8 deer kills to coyotes. By comparison, mountain lions were thought to be responsible for kills of 1 elk and 7 deer. One deer looked like a wolf killed it. Causes of death were unknown for the remaining 4 elk and 7 deer.
But, you must admit it's a pretty meager toll for an estimated 15-20 coyotes, 4 lions (2 subadults) and 3 wolves that were known to occupy the Game Range from time to time last winter.
What would explain it?
After only four years of study, winter weather is emerging as an obvious factor influencing predation success and deaths from all causes on the Game Range. Jamie began his annual survey in the hard winter of 1997, when he counted a record 66 deer and elk carcasses. The following winter was quite mild, resulting in a count of only 24 carcasses. The winter of 1999 was intermediate in weather severity, and yielded an intermediate carcass tally of 39. Last winter was mild again, with the expected low carcass count of 28.
Verified predator-kills followed trends in weather severity as well. The hard winter produced 13 elk and 20 deer carcasses that could be confirmed as predator kills. The following mild winter resulted in only 2 elk and 9 deer confirmed killed by predators. After the moderate winter of 1999, Jamie and crew confirmed 7 elk and 12 deer killed by predators. Last winter, we had 1 elk and 16 deer killed by predators.
How does weather affect what predators kill in winter?
The obvious answer is that deep snow and cold weather make large prey like elk and deer easier to find and overpower. I'm reminded of the researchers in Colorado many years back who captured and collared elk floundering in deep snow by jumping out of a helicopter beside them and hanging on. Try that method on dry ground and see what happens!
When Ross Baty was doing his master's research on the Game Range in the early 1990s, he observed that coyotes would travel on crusted snow on ridgelines and ambush deer out of their nearby beds in deep, soft snow. The coyotes had the advantage of springing from a firm base, while the deer were up to their ears in soft snow from the very first step.
I've generally assumed that severe winter weather conditions give predators an advantage over deer and elk. Maybe it's more accurate to say that severe weather evens the odds and allows predators a chance to prey more effectively.
Severe weather may also influence a predator's appetite. The more energy an animal needs to keep warm, the more food it must eat. It is known that predation rates decline in summer, compared with winter, so it is reasonable to expect predation rates to vary slightly as weather varies in winter.
Mainly, I conclude that our problems with low calf survival in the Game Range elk herd are not caused by carnage on the winter range. But, the pace of predation may be picking up right now as elk give birth to this year's calf crop along their spring migration routes.
I'm going to be making a little migration of my own for the next couple of weeks. So, I'll see you when the June rains have replenished our declining soil moisture and the creeks are running bank full again. Right?