How Variation in Activity Time and Duration at Water Sources Affects Feral Horse Vulnerability to Cougar Predation in Southern Nevada

Feral horses have become prominent in the Intermountain West. Approximately 43,000 horses are found in Nevada alone. With increasing numbers, they have become a large portion of ungulate biomass. Thus, it is important to understand their behavior, as they become integrated into western wildlife communities. However, little research has been conducted on the ecology of feral horses, and their relationships with native ungulates, carnivores, and local resources such as water. To address these concerns, I outlined three objectives: (1) determine if horses changed their water visitation activity times in relation to temperature. As a primarily diurnal species, we were interested in discovering if they showed more crepuscular behavior during bouts of hotter temperatures to combat heat stress and water requirements. (2) to determine if horse water behavior varied seasonally and (3) compared the timing and frequency of horses and deer visitation to water sources across seasons. Horses are water dependent, meaning they need water daily to maintain good fitness. During times of lactation, mares require upwards of 21 gallons per day. We observed water visitations of mule deer and feral horses to two permanent springs in two mountain ranges in Southwestern Nevada. From 2021-2023 we set up cameras at two springs to monitor the frequency and timeline of horse and wildlife visits to perennial sources of water. Our results indicated predictable behavior, especially during the hotter months of the year. Horses visited water sources more frequently during the summer months (April - October) as compared to the winter months (November - March). During summer, horses primarily visited water during diurnal and crepuscular hours. However, during winter, horses visited during nocturnal hours more frequently. Similarly, mule deer detections showed more visitation during diurnal hours in winter. To contrast, during summer, mule deer visited water nocturnally in addition to diurnal hours. Future resource is needed to see how this behavior affects their vulnerability to predation as well as how dominant horse presence at water sources affects the behavior of native ungulates, such as mule deer. Future discussions of water dominance are needed to determine if the feral horse populations limit access to water of the other wildlife in southern Nevada, including elk and deer.