Mule Deer
Medium-sized deer found throughout Colorado with distinctive, large ears.
About This Species
There are two species of deer in Colorado. Mule deer "mulies" have rope-like tails, evenly forked antlers and extravagant ears and bound with stiff-legged gait, the tail held down.
Mule deer are an icon of the American West, an economic resource and an indicator species for the health of important landscapes. Colorado plays host to the largest population of mule deer in the world.
Mule deer evolved in North America, so they are well-adapted to western landscapes. Since the mid-19th Century, mule deer populations across the western U.S. have experienced dramatic swings, mainly in response to human activities, severe winters and drought. Wildlife managers across eleven western states have spent decades trying to understand and address swings in mule deer populations. A 2004 report, produced by Western Association of Fish and Wildlife Agencies' Mule Deer Working Group, concluded that habitat loss, declining habitat quality, weather, population management, predation, disease and interactions with elk all influence mule deer populations.
Disease
Chronic Wasting Disease
Chronic wasting disease (CWD) is a fatal neurological disease found in deer, elk and moose. Colorado Parks and Wildlife researchers and biologists have studied chronic wasting disease on numerous fronts - their work and expertise on this disease is recognized both nationally and internationally.
Conservation and Research
Researching and Protecting Mule Deer
Mule deer populations in Colorado have shown dramatic fluctuations since the 1960s with the most recent decline in the 1990s. Colorado Parks and Wildlife has focused research efforts on developing management techniques to increase the health and survival of mule deer, an economically and ecologically important game animal.
Energy development in western Colorado has the potential to negatively impact mule deer populations. These impacts include habitat fragmentation and destruction, increased deer-vehicle collisions, increased noise levels, and more. Thus, this project aims to identify habitat improvements and energy development practices that will sustain mule deer populations for future recreational and ecological values.
Researchers selected the Piceance Basin as the project's study area because the basin contains some of the largest natural gas reserves in North America. Piceance is also home to one of Colorado's most important mule deer populations.
Research Objectives
- To determine the effects of energy development on mule deer behavior and population trends.
- To determine if habitat improvements benefit mule deer populations exposed to energy development activities.
- To identify energy development practices that will minimize impacts to mule deer populations.
During this long-term project, researchers will track mule deer habitat use and behavior, observe animal health throughout the winter season, monitor fawn survival and estimate mule deer populations in the study area. Finally, researchers will determine the success of different habitat improvements in reducing disturbances caused by energy development and in improving winter condition of mule deer.
The results of this project will show wildlife managers and energy developers if it is ecologically and financially valuable to mitigate disturbances in highly developed areas versus focusing efforts in nearby less or non-impacted areas.
Collaborators
- Bureau of Land Management
- Colorado State University
- Idaho State University
- Energy corporations
For many decades, wildlife managers have used habitat management as a way to increase the health and survival of mule deer, but the effect of these efforts had not yet been evaluated. Evaluating these efforts was the focus of this 4-year study to measure the health and survival of mule deer herds during the winter months in areas treated with different levels of habitat management.
Research Objectives
- To evaluate the impacts of large-scale vegetation habitat treatment on mule deer survival and health during the winter.
- To develop habitat management strategies for the benefit of deer.
- To put research results into context with historical records and recent declines in mule deer herd populations.
In the course of this study, researchers monitored fawn survival, mule deer body conditions, and population densities in areas with different levels of habitat management. Habitat treatment varied from mechanical disturbance in the form of hydro-axe clearing and roller-chopping of late seral stage pinyon-juniper forests, chemical control of weeds, and reseeding with desirable mule deer browse species.
The results of this study will help managers select the most effective habitat treatments to apply to mule deer winter ranges.
In the 1990s, mule deer populations began to decline across the western United States. CPW researchers set out to identify reasons for the decline, focusing on those factors that could be controlled through management efforts. Researchers recognized both habitat quality and predation as possible factors, but did not know which one played a larger role in mule deer population declines. To evaluate habitat as a limiting factor, researchers measured the effect of habitat enhancements on mule deer survival and fawn recruitment during a six-year study.
Research Objectives
- To evaluate the importance of habitat quality on mule deer population dynamics.
- To determine management priorities to reverse mule deer population declines.
During the winter months, researchers artificially enhanced habitat quality by distributing feed supplement pellets around the study area to improve deer nutrition. Predation levels were left unchanged. Researchers then measured pregnancy rates, doe body condition, and doe and fawn survival rates in the supplemented area and in an un-supplemented control area. Halfway through the study, the treatment and control areas were reversed in a crossover design.
Fawn survival in the supplemented area was significantly greater than in the control area during the winter, which resulted in a positive rate of population increase. These results provide clear evidence that nutrition and habitat quality were important factors contributing to deer population declines.
This project aligned with a research project conducted by the Idaho Fish and Game Department, which found that predator control had a smaller positive effect on declining mule deer populations.
Although completed in 2005, this project still serves as a reference and basis for many of Colorado Parks and Wildlife's current research projects. This project also helped wildlife managers determine factors that could be managed to reverse mule deer population declines.
- The story of Colorado's mule deer
- Colorado west slope mule deer strategy, public engagement report / submitted to Colorado Parks and Wildlife by the Keystone Center
- Plant and mule deer responses to pinyon-juniper removal by three mechanical methods
- A noninvasive automated device for remotely collaring and weighing mule deer
- Using maternal mule deer movements to estimate timing of parturition and assist fawn captures
- Mortality of mule deer fawns in a natural gas development area
- Herbivore body condition response in altered environments: mule deer and habitat management
- Density dependence in mule deer: A review of evidence
- Effects of male-biased harvest on mule deer: Implications for rates of pregnancy, synchrony, and timing of parturition
- Habitat management influences overwinter survival of mule deer fawns in Colorado
- Quantifying spatial habitat loss from hydrocarbon development through assessing habitat selection patterns of mule deer
- Landscape and anthropogenic features influence the use of auditory vigilance by mule deer
- Effects of helicopter capture and handling on movement behavior of mule deer
- Habitat selection by mule deer during migration: effects of landscape structure and natural-gas development
More Information:
Physical Characteristics
Mule deer are 31 to 42 inches at the shoulder and 4 to 7 feet from nose to tail. The tail, which is narrow and tipped with black, is 4 1/2 to 9 inches long. Adult bucks weigh from 121 to 331 pounds, with an average around 200 pounds; does average around 150 pounds.
Bucks shed and regrow antlers annually, which bifurcate (fork) as they grow.
Range
Mule deer are plentiful through much of Colorado, including urban areas, migrating throughout the year.
Habitat
Mule deer occupy any "edge" habitat, including suburban residential areas.
Diet
Deer are browsers, feeding mostly on woody vegetation, including twigs and leaves of shrubs and trees, including ornamentals. They also forage on crops, especially corn. Because they eat little grass, they tend not to compete seriously with livestock or elk.
Reproduction
Mule deer mate in the fall during the rut, where bucks fight for the right to pair with does. Does are only in estrus for a few days, but if mating is unsuccessful, can go back into estrus within a month in order to become pregnant.
Gestation is 190 to 200 days, with a pair of fawns being born in spring. Fawns stay with their mothers during the summer and are weaned in the fall, but may continue to stay with their mothers for up to two years.
Threats to Species
- Vehicle conflict
- Climate change
- Human development
- Predation by feral dogs
- Contagious diseases such as chronic wasting and hemorrhagic disorder