In contrast to elk, mule deer showed less measurable response to various recreational trail (off-road) use (Wisdom et al. 2004). Movement response increased slightly during periods of all four off-road activities except ATV riding. Deer may well be responding to human activity on trails with fine-scale changes in habitat use rather than substantial increases in movement rates and flight responses. For example, it is possible that deer may respond to that activity by seeking dense cover, rather than running from the activity. If mule deer are spending more time in dense cover, in reaction to any of the off-road activities, this could result in reduced foraging opportunities and a subsequent reduction in opportunities to put on fat reserves during summer that are needed for winter survival.
The amount of activity on roads as measured by the number of vehicle passes per day resulted in greater displacement distances from roads for mule deer (Sawyer et al 2009). As few as 2-6 vehicle passes per day resulted in an observed average displacement distance of 2.61km (1.61mi). Sawyer’s study reported 6-12 and 86-90 vehicle passes per day resulted in mule deer displacement distance from roads at an average of 4.30 and 7.79 km respectively. Sawyer concluded that displacement of mule deer may be reduced by achieving a reduction in daily traffic volume.
Winter range forage and habitat for mule deer is becoming increasingly limited in Colorado and has decreased over time due to residential development, livestock grazing, and recreation. Mule deer are highly vulnerable to stress and recreational disturbance during the winter and early spring when they have limited energy reserves and are struggling to maintain body condition (Thompson and Henderson 1998). Ungulates need to minimize energy expenditure to enable survival during this time when food is scarce and lower in quality (Moen 1978).