Mule Deer Study Reveals Opportunity for Further Examination

CPW sees opportunity in latest mule deer study

CPW_SiteLogoDENVER – Colorado Parks and Wildlife researchers see opportunity for further study and discussion after results of a recent mule deer study were published in Global Change Biology today.

CPW, who participated in the published study, along with other collaborators, agree habitat loss and degradation have long been assumed to be among the greatest factors causing mule deer declines. For the past few decades, western state fish and wildlife agencies have been concerned about the status and trend of mule deer populations.

In 2014, CPW held a series of public meetings across the state to obtain input regarding observed declines in mule deer herds. Participants identified several factors suspected of contributing to lower deer numbers, including barriers to migration, competition with elk, disease, doe harvest and hunting demands, declining habitat quality, habitat loss, highway mortality, predation, recreation impacts and weather.


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Mule-Deer-CPW-6652881c-c4bf-4c14-bc77-e34119fcc795The latest mule deer study analyzes the association of weather, energy development and residential development with early winter mule deer fawn recruitment in Colorado. Because the study was based on observational data rather than experimentation, the results do not infer a cause and effect relationship. A negative relationship between residential development, oil and gas development and certain weather conditions and early winter recruitment of mule deer fawns (annual December doe:fawn ratios) was reported. As residential development increased, the association of decreasing early winter recruitment of young mule deer was about twice that of other factors like energy development or weather factors. The period of study for this report largely pre-dates regulations adopted in late 2008 by Colorado’s Oil and Gas Conservation Commission, regulations intended to reduce the impact of oil and gas development on wildlife, including mule deer.

As identified in CPW’s West Slope Mule Deer Strategy, factors affecting mule deer population trends are likely numerous. Annual fawn survival is likely driven by the cumulative effects of various land-use changes and a variety of other factors that were outside the scope of the published study, such as forage conditions, disease, predation and competition with elk.

CPW is currently developing proposals to examine the role of predation in limiting mule deer numbers and also seeks to identify the benefit of habitat enhancement projects currently underway.

In yet another, ongoing mule deer study, slated for publication later this year, CPW has observed that deer in areas of higher disturbance density exhibit reduced avoidance to development features when compared to areas of lower disturbance densities. Past and present CPW research in the Piceance Basin of northwest Colorado suggests that despite declines in the annual ratio of fawns to adult does during December, winter fawn survival has more than doubled since the early 1990s. Both these studies illustrate the complexity involved in addressing factors influencing mule deer populations.

The continued effort to expand knowledge of these factors and inform wildlife management is the focus of CPW as well as other fish and wildlife agencies.

As the Western Association of Fish and Wildlife Agencies observed in 2011, “The capability of habitat to sustain wildlife into the future will depend on effective project planning and mitigation developed through constructive collaboration among federal land management agencies, state, provincial, and tribal wildlife management agencies, private landowners, industry, and other conservation partners.”


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CPW looks to use results from this study and others in concert with the West Slope Mule Deer Strategy to prioritize deer ranges for conservation that are particularly vulnerable to future development, and also improve collaborative efforts to enhance mule deer populations and their habitat.

Editor’s Note: “Increases in Residential and Energy Development are Associated with Reductions in Recruitment for a Large Ungulate,” appears currently in Global Change Biology. Authors include: Heather E. Johnson, A. Andrew Holland, Eric J. Bergman, Trevor Balzer and James Garner of CPW; and Jessica R. Sushinsky and Sarah Reed of WCS and CSU.

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CPW is an enterprise agency, relying primarily on license sales, state parks fees and registration fees to support its operations, including: 42 state parks and more than 350 wildlife areas covering approximately 900,000 acres, management of fishing and hunting, wildlife watching, camping, motorized and non-motorized trails, boating and outdoor education. CPW’s work contributes approximately $6 billion in total economic impact annually throughout Colorado.


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