Executive Summary: Elk Population Estimates and Forecasts for Rocky Mountain National Park, 2009-2011

Hobbs, N; Hoeting, J

EXECUTIVE SUMMARY: We used modern statistical methods to bring together four decades of monitoring data with a mathematical model of population dynamics to estimate the current and future abundance of elk in Rocky Mountain National Park. Our purpose was to support decisions on elk management in the park in way that is explainable and defensible. Model estimate of elk population size tracked the observed increase and decline of the abundance of elk in Rocky Mountain National Park during 1970-2009. We estimated that the downward trend in elk numbers seen during the last decade may have stabilized in 2009. Model estimates of the 2009 population size and forecasts for 2010 and 2011 were steady at about 600 animals, although there was considerable uncertainty in the forecasts. There is a high degree of certainty that the current population is within or below the target range specified in the Elk and Vegetation Management Plan, 600 - 800 animals. Looking two years ahead and assuming moderate culling of 30-50 adult females, there is a 75-80% chance that the population will remain below the upper limit of 800 animals. However, there is also a significant chance (about 40-50%) that the population will fall below the lower threshold of 600 animals during 2010-2011. The effects of increasing harvest outside the park during the past decade, culling within the park during 2008 and 2009, and treatment of a significant number of reproductive females with a persistent contraceptive have combined to reduce the elk population to levels that are within or below the target range specified in the elk management plan. It has been wisely said1 that predictions are difficult, particularly when they involve the future, and our forecasts do not escape that difficulty. The model’s near-term forecasts indicate there is some probability that the future population could exceed the upper limit of the target range, but that risk is substantially smaller than the risk that the population might continue to decline. Although the number of elk harvested from the area surrounding the park was lower in 2009 than during any year in the previous decade, the effects of reductions in the number of animals harvested were more than offset by effects of culling within the park and by the depressing effect of fertility control on recruitment. These effects create a risk that elk numbers might reach unacceptably low levels within the park if culling is continued in the absence of reductions in harvest around the park boundary.

Executive Summary: Elk Population Estimates and Forecasts for Rocky Mountain National Park, 2009-2011

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