From southern Alaska to northern Mexico and the Pacific Coast to the Rocky Mountains, classical mule deer (Odocoileus hemionus) abound. They call western North America home. With a population ranging from 3–4 million, these tough species derive their name from their massive, mule-like ears. While some areas have steady herds, others experience reductions brought on by environmental conditions, predators, and human activity.
Habitat Loss
Once-continuous ranges broken up by roads, houses, and businesses greatly restrict migration routes and access to seasonal feeding spots. In certain areas, rapid urbanization along valleys and slopes in states like Utah and Colorado has decreased mule deer’s winter range—vital for their survival during the harsh months—by as much as half. Deer’s stress levels are raised and their population’s resilience is lowered as habitat loss drives them into ever smaller and inappropriate areas.
Deforestation mostly results from logging, farming, and infrastructure building, therefore depriving mule deer of their main food and cover source. While a variety of forest cover gives cover from predators, open shrublands give these deer food supplies including sagebrush, bitterbrush, and aspen shoots.
Mule deer flourish in woodland areas reduced by clear-cutting in places like the Pacific Northwest. Agricultural conversion has replaced native plants in the Great Basin with crops mule deer cannot consume. Particularly in the winter, deer are more susceptible to predators and malnutrition when there is less cover and food.
Predation
Natural predator populations of mountain lions and coyotes have recovered in several regions across the mule deer range, hence increasing pressure on deer herds. Highly effective hunters, mountain lions flourish in difficult terrain where mule deer hide-out; studies in areas like Utah suggest that each lion can kill up to one deer every week.
Although they pose less of a hazard to healthy individuals, coyotes particularly in open environments strongly target weak fawns. Particularly when prey is already challenged by other circumstances, this increase—partially due to declining hunting of predators and habitat overlap with expanding deer ranges—has resulted in localized losses in mule deer numbers.
Disease
Chronic wasting disease (CWD), a fatal brain disorder brought on by prion, is progressively threatening mule deer populations all throughout North America. By March 2025, chronic wasting disease (CWD) has expanded 26 states in the US and many provinces in Canada from its 1960s discovery in mule deer in Colorado.
Like in Wyoming and Saskatchewan, in high-prevalence areas this illness has killed out as much as 40% of herds and caused weight loss and erratic behavior. Lack of a vaccination or treatment makes chronic wasting illness a danger to population stability in places where deer congregate at specific seasons.
Because of their migratory patterns and social character, mule deer are a perfect vehicle for the quick spread of disease both inside and between herds. Close contact in winter helps to spread chronic wasting disease (CWD) through saliva, urine, and feces as deer gather in lower-elevation areas to withstand challenging conditions.
Respiratory droplets or biting insects allow various diseases including pneumonia, epizootic hemorrhagic disease (EHD), to proliferate in these dense populations. Overcrowding causes habit loss, which in turn raises this risk and turns daily activities into possible epidemic that might wipe off local populations in one season.
Conclusion
Mule deer are threatened in several ways that compromise their existence over western North America. Urbanization, destruction of forests, and wildfires—which reduce food and cover—are destroying their habitat. Rising mountain lion and coyote numbers as well as imbalances brought on by human activity make fawn survival rates extremely sensitive. Then, using the absence of immunity and intimate contacts of the herds, diseases like chronic wasting disease (CWD) mercilessly sweep over the herd. These issues taken together jeopardize the existence of a species essential to ecosystems and human civilization.
FAQ’S
Are mule deer populations declining?
Mule deer populations began declining in Oregon in 1981 from 300 000 individuals to 164 000 in 2022 (Oregon Department Fish and Wildlife 2021).
Where is the largest population of mule deer?
western Colorado
Some of the largest herds are found in western Colorado and Wyoming, which draw hunters and wildlife watchers from across the country.
Are there more deer now than 100 years ago?
Today, estimates put that number around 30 million.
Is there a deer overpopulation problem?
Over-abundant deer populations also reduce the diversity of plants and other wildlife species found in the forest.