- Mule deer populations have declined significantly across much of the western U.S. since the 1990s.
- In some western states, mule deer numbers are less than half of what they were in the mid-20th century.
- Black-tailed deer populations have also declined in parts of their range, particularly in British Columbia and northern California.
- Southern Vancouver Island has experienced sharp declines in black-tailed deer populations in recent years.
- Sitka black-tailed deer populations in Southeast Alaska are vulnerable to periodic crashes following severe winters.
- Mule deer fawn recruitment rates are declining in several states due to predation and poor habitat conditions.
- Mule deer in Colorado have decreased by over 200,000 since the early 2000s.
- California’s black-tailed deer population is estimated to have declined from over 2 million in the 1960s to around 500,000 today.
- British Columbia’s Columbian black-tailed deer have seen local population reductions due to disease and predation.
- Deer harvest numbers have dropped in many states as a reflection of lower population densities.
- Urban sprawl and land development are major drivers of mule and black-tailed deer habitat loss.
- Habitat fragmentation limits seasonal migration routes critical for mule deer.
- Road construction and increased human access disrupt traditional movement corridors for both species.
- Wildfire suppression has led to dense, mature forests that no longer support quality forage.
- Intensive logging practices in coastal forests have replaced diverse habitats with monoculture tree plantations.
- Dense, stem-exclusion forest stands provide minimal food or cover for black-tailed deer.
- Loss of riparian habitats reduces water and forage availability for mule deer in arid environments.
- Sagebrush-steppe conversion to agriculture has significantly reduced mule deer range in some regions.
- Energy development (oil, gas, and renewables) fragments large areas of mule deer winter range.
- Black-tailed deer are especially sensitive to loss of thermal and escape cover in coastal forests.
- Wildfire can temporarily improve deer habitat by promoting new plant growth.
- However, large, high-severity wildfires can eliminate critical cover for both mule and black-tailed deer.
- Mule deer are vulnerable to wildfires that destroy low-elevation winter ranges.
- Climate change is altering plant phenology, making it harder for deer to time migrations with peak forage.
- Warmer winters may reduce snow cover, increasing predator access to deer across a wider area.
- Drought conditions in the Southwest and California have lowered forage quality and water availability for mule deer.
- Changes in snowpack timing affect Sitka black-tailed deer overwinter survival in Southeast Alaska.
- Increased fire frequency in interior forested areas can lead to long-term habitat instability.
- High road density in post-fire landscapes raises mortality risks due to predators and hunting pressure.
- Invasive plants post-wildfire can reduce nutritional value of regenerating deer forage.
- Mule deer face significant predation pressure from coyotes, mountain lions, and, in some areas, wolves.
- Black-tailed deer are often preyed upon by cougars, black bears, and wolves, particularly where cover is reduced.
- Increased road access facilitates predator movement into deer habitat.
- Fawn mortality due to predators is one of the primary causes of low recruitment in many regions.
- Vehicle collisions kill thousands of mule and black-tailed deer annually across the West Coast and Rocky Mountains.
- Poaching and illegal harvest, though hard to quantify, remain an ongoing issue in remote areas.
- Domestic dogs pose an emerging threat to urban-edge black-tailed deer populations.
- Predators are more effective in logged or burned areas where deer have fewer hiding spots.
- In heavily hunted regions, mature buck age structure is declining in both species.
- Seasonal hunting pressure in accessible areas may further stress declining herds.
- Chronic Wasting Disease (CWD) continues to spread among mule deer populations in the Rockies and Plains.
- Black-tailed deer on Vancouver Island have suffered major mortality events from Adeno Hemorrhagic Disease (AHD).
- Mule deer infected with CWD often show no visible symptoms until advanced stages, complicating management.
- Disease surveillance in black-tailed deer is often limited due to remote, forested habitats.
- Deer density in small habitat patches can increase disease transmission rates.
- Fecal DNA studies have been used to track health and genetic diversity in black-tailed deer herds.
- Drought and poor nutrition weaken deer immune systems, making them more susceptible to disease.
- There is growing concern about potential overlap between CWD-infected mule deer and black-tailed deer populations.
- In some areas, public reporting systems are now being used to monitor black-tailed deer disease outbreaks.
- Disease outbreaks combined with habitat loss create compounding threats for long-term population stability.