Yellowstone elk numbers and wolves
Feb. 18, 2003
It's been a while since I did a full article on this, but past stories and figures about wolves and numbers of elk are quickly forgotten in the current atmosphere of politically-induced Alzheimers.
Montana and Wyoming anti-wolf politicians are in full throttle roaring how wolves have "decimated1" elk in Yellowstone Park. They like to point to the northern range elk herd, which seems to have declined in size since 1993, especially if you present the figures in certain ways. They don't say much about other elk herds in Wyoming or Montana because the number is steady, they are less well known, or figures are not readily available.
It's time to review again some of the numbers.
The record high count of northern range elk was taken over a 4-day period in January 1994. 19,045 elk were counted. The estimated number was 19,359 elk. This was a high count, not the herd average. The previous winter the estimated number was 18,088 elk. The winter before that 15,587 elk, and in the official count taken Feb. 6, 1991, only 9,456 elk were counted, but the estimate was 10,287 elk. From these data it is evident that wide fluctuations in population were present.
A statistician will tell you that if random events are present any high peak figure or valley low figure is likely to decrease, if it's a peak, or increase if it's a valley, within a short time. This phenomenon is called "statistical regression toward the mean." This appears to have been underway before the wolves were introduced in March 1995. The elk count taken Dec. 21, 1994 was 16,791 actual elk counted and 17,290 estimated. See http://www.nps.gov/yell/nature/northernrange/appendixb.htm for these figures and many more.
Unfortunately, no official count was made during the winter of 95-96 or the very critical winter of 96-97 when thousands of elk starved. The unofficial count in the spring of 1997, however, was just over 10,000 elk on northern range. Here are the counts taken since: December 1997- 13,400; December 1998 - 11,742; February 1999 - 11,742; December 27, 1999 - 14,538; early 2001- 13,400; December 2001- 11,969; Jan. 2002- 9,215 actual count. I gathered these figures from various newspaper stories and Park news releases because I couldn't find a single official Park Service summary on-line for years beyond 1994. Folks should remember there is a late elk hunt just north of the Park. Each year hunters kill from about 500 to several thousand elk. This explains why the count was 11,742 in Feb. 1999 (after the hunt); but 14,538 in December 1999 when the hunt had just begun.
The big news was this January when the "Northern Yellowstone Cooperative Wildlife Working Group" (the official counters) counted just 9,215 elk in a one day period (counts aim for just one day to avoid double-counting elk that move over the period of several days). 6,897 elk, or 75 percent, of the elk were inside the Park boundaries. 2,318 elk were counted north of the park. The count's accuracy was described as "poor" due to bad counting condition (brown elk on brown grass or on patches of snow and grass). Nevertheless, anti-wolf politicians seized on this saying the size of the herd had been cut in half (using the highest figures ever recorded (January 1994) and comparing them to the low 9215 elk count of January 1994.
A surprising separate elk count-
Today I learned that a separate count has been done each winter in recent years. In conjunction with the wolf winter study an additional elk count is done. It was done in November 2002 after a snowstorm when counting conditions were good. It was done over a 4 day period, so elk movement could be potentially a problem, but Dr. Doug Smith said elk movements appeared to be minimal. Counting were Smith and the dean of Montana elk counting, Dave Stadley, whose experience counting elk dates to 1952. The number? It was 11,653 actual elk counted. This was before the late elk hunt. Remember that the pre-hunt count slightly over a year before, December 2001, was 11,969. Perhaps some of the difference was due to the hunt as well as the poor counting conditions/
I'll leave it to you to conclude whether the northern range herd is in deep decline, and further, if so, are wolves responsible?
How many elk does each wolf kill?
These figures have been batted around a lot lately. The only good figures over several years come from the winter wolf studies on the northern range. There is an early winter study when prey are strong and a late winter study when prey after weaker. The average since the winter studies began was 1.4 elk per wolf per month for the early study and 2.2 elk per wolf/month in the late winter study. The average is 1.8 elk per wolf. People multiply that by 12 and come up with 21.6 elk per wolf a year. However, there are some caveats. Yellowstone is a multiple predator system. Prey not quickly consumed by wolves is often lost to bears, coyotes, eagles, and especially magpies and ravens (where did that word "ravenous" come from anyway?). Wolves may have to kill more prey in much of the Greater Yellowstone to make up for losses to scavengers as compared to Idaho.
Good studies on summer predation do not exist. However, it is known that wolves lose weight in the summer through the fall. That is one reason why so many radio collars drop off then. Fall is the toughest time for the wolf and late winter the easiest. Studies on summer predation are about to begin because 4 wolves now have GPS collars so they can be tracked 24 hours a day, including the much harder-to-observe summertime.
It would be nice if such studies could be done in the other major wolf area -- Idaho. I have a hypothesis that Idaho wolves gain a great benefit in what is usually their toughest time -- fall -- from deer and elk hunters with numerous gut piles and escaped, but wounded prey for the wolves to take down. It is also possible, however, that hunters kill enough wolves illegally to make up for the food advantage they provide for the wolves.
Folks may be interested in the last major article did on this matter. "Montana Group continues to argue wolves have decimated the Yellowstone Elk. Is this likely?" Dec. 23, 1999 (with several updates).
1A note on "decimate." This word is commonly used. "The wolves have decimated our wildlife." This probably indicates that anti-wolf politicians read the same email. The word comes from the Roman practice of killing one out of every ten soldiers as group punishment. The original meaning seems to have been superseded to mean "destroy almost completely."
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