Game Range Ramblin's
Game Range Articles
by Mike Thompson,
FW&P wildlife biologist,
writing for the Pathfinder
March 1, 2001
Seeley Swan Pathfinder
Seeley Lake, Montana
by Mike Thompson
It's kind of funny how one thing often leads to something entirely different.
A legislative auditor attended our public meeting last week about Phase II of the 50th Anniversary Project. His presence made me think about the countless supporting documents strewn about my desktop, forming distinct geologic strata according to the period of EIS-writing in which they were deposited.
Auditors usually tolerate a few papers stuck together with a stray coffee splatter or chocolate fleck. However, they do tend to balk when soil forms and plants grow in your paper trail.
So, I thought I'd better get my files in order. In the excavation process, I rediscovered a letter from Bob Wasson, who wrote in reply to a meeting we held in Seeley Lake back in mid-January. At that time, our minds were on hunting regulations, and numbers of elk and deer available for hunting. By grasping one free corner of the letter with a tweezers, and using a knife blade to gently peel back a greasy pile of memos on top, I was able to extract Bob's letter with minimal damage. After a light brushing with a soft-bristled toothbrush, an archeologist was able to decipher the now precious words. Apparently, Bob wrote:
"After the 'listening session' last night in Seeley Lake, it occurred to me that there is yet another influence that may interact with the cow/calf ratio . . . I note in the February 2001 issue of Alaska magazine that there is a study of moose ongoing in Alaska. The objective of that study is to find the relationship of diet and calf recruitment. Actually, the relationship of body fat to winter survival."
"My point is that for decades, the forests in this valley have been [logged], with the net result of thousands of acres becoming (for a short period of time) open spaces where graze and browse have a chance to bask in the sunand ultimately feed the wild world. In recent times, the forestry practices on the National Forests have changed, and primarily, only privately owned lands continue to be harvested. The net result is a huge reduction of food available for the animals to build body fat for the subsequent winters. A simple measure of this effect may be a count (%) of twins/triplets in deer recruitment."
Which brings me back to the topic of low ratios of calves per 100 cows in our elk population. As you may recall, we observed only 23 calves per 100 cows during our latest annual helicopter survey of the Game Range on January 6-7. That's virtually the same ratio we observed the year before and the year before that. We've seen mid-winter calf-cow ratios fall below 30 in 6 of the last 7 years, whereas we never observed a ratio below 30 from 1988 through 1993.
I think Bob is probably on to something with the theory of changing habitat. But, he also raises a very interesting point when he suggests that we should see effects in percentages of fawns in deer populations.
Biologists are not seeing a long-term decline in fawn-doe ratios in white-tailed deer and mule deer populations, like we are with calf-cow ratios in elk. So it seems we're looking for a causative factor, or more likely a combination of factors, that hits calf elk harder than adult elk, but affects fawn and adult deer about equally.
We're also looking for a set of factors that seems to have had the same effect on elk calves all across the more heavily forested portions of the so-called inland northwest, from the Continental Divide in Montana to eastern Washington. In fact, calf-cow ratios in portions of northern Idaho have been consistently lower than we are experiencing here, and for a longer period of time.
If we're going to find a single predator or group of predators to blame, it would have to be one that is common across the northern Rockies, where we're seeing the low calf-cow ratios. One of the most common predators that increased in numbers in the early to mid-1990s is the mountain lion. And, lions do tend to prey on calves at a higher rate than on adult elk. However, by all indications, lion numbers are now at least as low in our area as they were when we routinely saw calf-cow ratios higher than 30 in the early 1990s. Calf survival rates have not twitched in response to the apparent sharp decline in lion numbers.
Now, I want to interrupt myself before I travel too far down the "predators" road this week. We've been there before. I have no news to report on predation, except for reminding you that Jamie Jonkel's annual surveys on the Game Range continue to verify that relatively little predation is occurring in our elk herd during the winter months.
But, as Bob suggests, we've never said much about the way forest succession on summer range could affect the calf-cow ratios we observe in January. It reminds me that for as long as I can remember, calf-cow ratios have tended to be quite a bit higher in populations located east of the Continental Divide in Montana than in those located west of the Divide. Why?
I have to admit, I always assumed it had to do with habitat quality, and the notion that preferred elk forage grows more abundantly on mountain slopes with lots of big, grassy parks and meadows, than under dense, extensive forest canopies.
However, life remains complicated. It could be that forested habitats also support higher numbers of predators that select elk calves as prey. For instance, we have far higher densities of black bears on the west side of the Divide than on the east side. If increasing forest canopy on summer range causes elk to produce lighter and less vigorous calves, why haven't we seen more calves on winter ranges since the huge Canyon Creek fire of 1988?
Why? It's the $64,000 question.