March 16, 2000
Seeley Swan Pathfinder
Seeley Lake, Montana
by Mike Thompson,
Montana Fish, Wildlife & Parks
"Game Range Ramblings" column Seeley Swan Pathfinder
What's that pinging sound in our elk population?
The graph that accompanies this week's column displays the bothersome "noise" that's been hiding in our annual counts of cows, calves, spikes, raghorns and older bulls on the Blackfoot-Clearwater Game Range.
Although the population's been running rough, it has been running. Results from this year's helicopter survey documented an increase from 842 elk in January 1999 to 856 one year later. It was just what we had hoped for when Montana Fish, Wildlife & Parks (FWP) recommended staying with a conservative set of hunting regulations for last hunting season.
But, our somewhat misleading population increase was built on a flush of spikes and raghorns that eluded hunters at unusually high rates last fall, with the aid of some awful hunting weather. And, a few more of the older bulls moved down to winter range this year, compared with 1999.
In fact, if not for your bad luck finding bulls last hunting season, FWP's elk counts on the Game Range this year would have shown a decline. The number of calves and cows actually dropped between 1999 and 2000. I wish we could blame a high hunting harvest because FWP can control hunting with regulations and enforcement. But, since 1995, FWP has issued only 50 A-7 licenses annually for the Game Range and hunters have killed no more than 24 cows per year (according to check station results). Back in the early 1990s, it took an annual allocation of up to 200 special A-7 licenses for the Game Range, and an annual kill of 80-101 cows per year, to curb the growth of this elk herd.
It's getting pretty hard to ignore that annoying hesitation in our elk population. And, as any good wildlife mechanic knows, if you want to check for spark in an elk population, you shine a light on its calf:cow ratios.
What is a calf:cow ratio? Well, in the case of the graph on this page, it might help to think of the calf:cow ratio as the percentage of cows that brought calves with them to the winter range. The higher the percentage of cows with calves, the higher the calf:cow ratio. Elk almost always give birth to a single calf, so variable twinning rates don't muddy up our analysis of calf:cow ratios in elk.
Ranchers have fits when they're told that calf:cow ratios in wild elk normally vary between 30 and 40 calves per hundred cows. In cattle ranching, you expect to get a calf from almost every cow, and a calf:cow ratio approaching 100 (maybe even higher than 100 if there are quite a few twins).
But, when ranchers talk about calf:cow ratios, they don't count the non-breeding heifers as part of the cow herd. In wild elk, we have to lump the nonbreeders (the 18-month-old and most of the 30-month-old females on the winter range) in with the breeding aged cows because we can't tell the difference from a helicopter. Judging from ages of harvested elk collected at the Game Range check station, about 25% of the elk we count as cows from the helicopter are actually too young to have calves with them.
Also, about 11% of our elk cows are over 11 years old, which also accounts for some of the lower production rates in wild elk, compared to a commercial cattle herd.
But, even wildlife biologists get a wee bit uncomfortable when midwinter calf:cow ratios dip below 30, as they have in 5 of the last 6 survey years on the Game Range. And, these disappointing results would be easier to live with if not for the fact that midwinter calf:cow ratios never fell below 30 in the previous 6 survey years (1988-1993).
It looks like things are changing, and not for the better if you're an elk calf. My first glance at the graph made me conclude that something drastic happened between 1993 and 1995. But, after a longer period of staring and pondering, I think the graph reflects a more gradual, downward trend in calf survival since the late 1980s.
I suggest you can see the "actual" trend better if you disregard the extreme highs in 1988 and 1993. I think calf survival in 1993 was bolstered by the short-term effects of the Game Range fire, which burned 5,000 acres of winter range in October 1991 and probably caused a flush of high-quality forage for pregnant cows on spring greenup in March-May 1992. Improved forage quality would have shown up in calf-cow ratios the following January (1993).
I don't have any clever theories about what caused the exceptional calf:cow ratio in 1988. But, like the pulse in 1993, it appears to me that calf:cow ratios of nearly 50 are only going to be seen in the Game Range herd under odd circumstances. Likewise, the low ratio of 12 in January 1998 was the result of stress on pregnant cows in the severe winter of 1996-97.
Throw out the extremeshigh and lowand we're left with the trend in calf survival under normal circumstances. This is how I conclude that the factors causing an apparent decline in calf survival have been bringing gradually increasing pressure to bear throughout the 1990s.
What are the possible causes of this trend that's making my job a lot more challenging? Let's talk about those next week.