Temporal Overlap Among Feral Horses, Cattle, and Native Ungulates at Water Sources

Feral horse (Equus ferus caballus) populations on public rangelands in the western United States threaten forage production for livestock and wildlife habitat. Interference competition between feral horses and heterospecifics at watering sources can have negative effects on livestock and wildlife. Researchers have documented altered timing and behavior of wild ungulates at water sources when horses were present. The few studies examining these interactions have infrequently occurred within areas specifically managed for feral equids and have not occurred in sites with cattle. We used motion-sensitive cameras at 8 watering sources to document watering activity patterns and construct indices of temporal overlap among feral horses, cattle, elk (Cervus canadensis), mule deer (Odocoileus hemionus), and pronghorn (Antilocapra americana) within the Adobe Town Herd Management Area in southern Wyoming, USA, between June and September 2018 and 2019. Feral horses, cattle, and pronghorn exhibited a high degree of temporal overlap (>79%) in water use, with feral horses and pronghorn exhibiting the highest estimated percent overlap (88.1%, 95% CI = 86.5-89.6%). Mule deer and elk watering activity also overlapped with horses and cattle but to a lesser degree (<55%). Feral horses spent a mean of 16.7 +/- 30.5 (SD) minutes during a watering event and were present at a given water source on average 4.5 +/- 6.3% and up to 34.9% of the day, which is less than reported in previous studies. Cattle spent on average 23.5 +/- 44.9 minutes during a watering event, and were present on average 4.2 +/- 7.7% and up to 42.4% of the day at a single water source. Results of generalized linear mixed-effects models indicated that number of conspecifics was the strongest predictor of visit duration for pronghorn and horses; hour of the day and group size of heterospecifics were informative, but less important, variables. There was no difference in peak visitation time for any species between sites of high versus low horse or cattle use. Despite temporal overlap, we did not find evidence of interference competition between feral horses, cattle, and pronghorn. We recommend future examination of interference competition and its biological consequences between introduced and native ungulates at water sources of varying size across sites, equid population levels, and livestock stocking rates. (c) 2020 The Wildlife Society.

Automated summary

The study found high temporal overlap in water use among feral horses, cattle, and pronghorn in a management area in the western United States, while mule deer and elk showed lower overlap with horses and cattle. Despite the temporal overlap, there was no evidence of interference competition between feral horses, cattle, and pronghorn.