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Sound the Alarm!

by HUPC Board Member Sharon Emerson

Mountain Lion by Margaret Pettis Mountain Lion by Margaret Pettis

A valuable lesson about Utah mountain lions is offered by a recent paper in Science Magazine entitled "False alarm over environmental false alarms." The article notes that we live in an uncertain world that requires a constant weighing of costs and benefits as a basis for action. We rely on scientists to alert us to a wide set of possible outcomes, many of very low probability, so that citizens can decide which demand action. One unavoidable outcome of this approach is that some warnings will prove to be unfounded and others will lead to actions that prevent or mitigate the predicted negative consequences. The important conclusion that this article reaches is that despite the potential for false alarms, the benefits of the scientific warnings outweigh the costs of their not always coming to pass.

The alarm is being sounded in Utah over the Division of Wildlife Resources (DWR) recommendation for a 20% increase in cougar kills in the 2003-2004 hunting season. The rationale for this increase is that predation by mountain lions is a significant cause of declining deer herds in Utah (see Salt Lake Tribune editorial, August 17, 2003). Concerned environmentalists have questioned the wisdom of this recommended increase and worry that cougar populations cannot sustain high hunting pressure.

Can science help us make an informed decision about whether we should be alarmed by the DWR recommendation? Are there data on which to base the recommended hunting increase? What are the benefits and costs of following the DWR recommendation? Wildlife biologists recognize four theoretical models for how hypothetical prey populations might be regulated by predators. Intense radiotelemetry and manipulative experimentation are necessary to test these ideas for any particular situation. To date, none of these models have been tested on populations of mule deer. Work on other prey species, however, suggests that predation does not cause prey population declines. It is unlikey therefore that mountain lion predation is responsible for Utah mule deer declines. More likely culprits include prolonged drought, contraction of winter range, and competition with elk.

Studies in arctic ecosystems suggest that in some cases (but not all) after prey species are depressed, predation can become an important mortality factor retarding or preventing prey population recovery. Unfortunately, detailed studies are necessary to identify such situations. Prey population must be compared in areas with and without predator removal.
must last over a long enough time that varying weather conditions occur. Confounding factors such as other predators, hunting and alternative prey species must also be measured. Such studies have not been done on any mule deer populations. Therefore, conditions that might allow predation to become an important mortality factor in altered ecosystems such as those where mule deer exist remain unknown.

The scientific approach is complicated even further by the limited information that DWR has on mountain lions. Knowledge of births, deaths, and the factors that affect them is essential to understanding the potential health and well being of any wild population. In fact this level of information is almost never available, and more indirect methods are customarily applied to estimate even the most basic population parameters such as the number of mountain lions in Utah. One way in which such estimates are obtained is to use published results from other studies that give an average home range size for an adult mountain lion and then extrapolate that onto potentially suitable habitat to arrive at an estimate of the number of mountain lions likely to be in a given area. This common practice provides a gross estimate appropriate for some types of wildlife decisions, but it cannot provide precise enough estimates for setting reasonable hunting levels of mountain lions. Furthermore, the lack of precision can have a significant negative effect by prescribing a hunting pressure so high that it will reduce mountain lion population numbers below sustainable levels.

In summary, the idea that killing more mountain lions will boost the Utah deer herd lacks scientific support. At best, the DWR recommendation will leave a small but viable population of mountain lions and the deer numbers rebound. But there is an equally plausible and alarming possibility that such heavy hunting pressure will push Utahπs mountain lion population toward extinction. In the absence of appropriate scientific information, we can only hope that the environmentalistsπ alarm regarding Utah mountainwill turn out to be one of those beneficial scientific warnings that doesnπt really come to pass.

Additional Reading
S., E. Bulte, J. List, and S. Levin. 2003. False alarm over environmental false alarms. Science 301: 1187-88.
W., D. Lutz, T. Keegan, L. Carpenter, and J. deVos. 2001. Deer-predator relationships: a review of recent North American studies with emphasis on mule and black-tailed deer. Wildlife Society Bulletin 29: 99-115.
Division of Wildlife Resources 1999. Utah Cougar Management Plan. 48 pp.

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