By TYLER J. BASKFIELD
Daily Press writer
The mule deer population has been on the decline in Colorado for some time and until recently the causes behind the decline have not been researched.
The Colorado Division of Wildlife (DOW) published a report to the Colorado Legislature called "Declining Mule Deer Populations in Colorado Reasons and Responses." The 50-page report reviews causes in the decline of the mule deer population.
The report follows the history of mule deer herds in Colorado. It states mule deer numbers have varied considerably historically, primarily in response to climatic fluctuations, habitat change and market hunting. According to the DOW, mule deer were not abundant before European-American settlement of the west. The report states somewhere between 1935 and 1955 mule deer populations reached their peak in the West. Since then mule deer populations have been declining and today mule deer number less than half of peak populations in the 1940s.
Even after the study the DOW has a hard time pinpointing what is causing the mule deer decline. According to the report, some evidence suggests numbers in the past may have been too large when populations peaked and that heavy browsing pressure combined with conversion of deer habitats to other land uses may have lowered the carrying capacity to current mule deer habitats.
Another reason the DOW points to as a catalyst of the decline is the suppression of wildfires and the increase in exotic plant species. This causes the quality of forage to decline and favors elk which find the exotic plant species more palatable.
Elk numbers have increased dramatically during the same time deer populations have decreased and, according to the report, elk could gain a competitive advantage over mule deer on rangelands commonly used by both species.
As far as the diseases that infect mule deer are concerned, the DOW stated these disease outbreaks are rarely widespread enough to account for statewide or regionwide declines.
Many people believe predators have played a role in the decrease of mule deer, but not according to the DOW report. The report states: "The only certainty is that predators kill and eat mule deer. However, studies that investigated responses of entire mule deer herds to intensive coyote control have failed to demonstrate that mule deer numbers increased as a result of coyote control. The contribution of predation to the mule deer decline remains uncertain."
Regarding excessive deer harvests, the DOW has a hard time believing these have led to a decline in population. The report states if the deer were being hunted so intensively the reproductive rates of does should be high and the mortality rates of fawns should be low. According to the DOW, studies show the opposite. Hunting has contributed to reductions in numbers of bucks in deer herds across Colorado.
The DOW study doesn't give one reason as the exact cause of the decline in mule deer. It points to the deterioration in deer habitat as the most likely cause, but quickly points out that few experiments have been conducted to test for effects on an entire herd scale. The DOW admits "As a result, the answer to the question 'What has caused mule deer numbers to decline?' remains both speculative and controversial."
In the future, the DOW plans to look deeper into the cause behind the decline and initiate programs and management actions to evaluate what can be done to remedy the deer decline.