In response to the sharp decline in mule deer numbers across Colorado, that state’s wildlife managers have scaled back the number of deer hunting licenses substantially.

Colorado Parks and Wildlife (CPW) data indicates a statewide deer population decrease of 36% since 2005. During this same period of time, the nation’s largest herd, which is located in northwestern Colorado, has dropped nearly 70%.

The exact cause of the decline is somewhat mysterious and has been the subject of recent study and research across the western United States. Colorado-based wildlife biologists have cited several potential factors:

“We certainly cannot have it all. We need to be smart about our wildlife habitat, especially our mule deer habitat and how we manage the population,” said Arizona-based wildlife biologist Jim Heffelfinger, who chairs the Western Association of Fish and Wildlife Agencies’ Mule Deer Working Group. “There are so many different things that are stressing mule deer around the West.”

In effort to boost deer populations, CPW leaders are holding a summit in Glenwood Springs next month.

“We’ve had a significant decline that is not satisfactory to us and to the public,” Chad Bishop, CPW assistant director for wildlife natural resources, told the Denver Post. “We’re going to work collaboratively with all of our constituents to increase mule deer numbers as best as we can.”

One topic that is likely to be discussed at the summit is the extent of oil and gas development on public land. “We work closely with energy companies, like we would any entity — work with them on achieving mitigation as best we can when energy impacts occur,” said Bishop.

The Bureau of Land Management (BLM) officials have said that they are planning for 15,000 wells to be drilled over the next 20 years on 1.5 million acres in northwestern Colorado. This region, located between Meeker and Rangely, south of the Yampa River and north of the Colorado River, is the habitat of the already-declining White River herd.

Conservationists are pushing for better allocation of oil and gas facilities, consolidation of facilities, limited construction of roads and adjustments to ensure that pipelines do not interfere with migration routes.

Unfortunately, the rights to develop oil and gas in that area are already leased, leaving officials with limited power.

“We are limited in what we can do once lands are leased,” said BLM spokesman Dave Boyd. “We’re looking at what can be done to mitigate oil and gas impacts…Should it turn out that it would be more than 15,000 wells, then we would need to do another environmental impact statement.”

One thing state officials do have absolute control over is the number of hunting licenses issued. In response to the recent deer decline, Colorado wildlife managers have reduced the number of hunting licenses they issue by nearly 39% since 2007, cutting back from 130,106 to roughly 80,000.

The reduction in hunting licenses has an immediate impact on funding for land conservation. Hunters and anglers have historically been — and continue to be — the largest contributors to government wildlife conservation programs. Through excise taxes and license revenues, they have contributed more than $10 billion dollars to conservation, and annually provide more than 80% of the funding for most state fish and wildlife agencies.

“If our deer continue to decline, it will hurt us financially,” said Bishop.

Colorado isn’t the only state facing challenges with the deer population. Across western states, deer numbers declined by about 10% between 2003 and 2009, according to Heffelfinger.