FERAL HORSES DISRUPT GREATER SAGE-GROUSE LEKKING ACTIVITY IN THE GREAT BASIN.
Diana A. Munoz; US Geological Survey/UC Davis; 800 Business Park Drive Suite D, Dixon, CA, 95620; (818) 531-5966; damunoz@ucdavis.edu; Peter S. Coates
Greater sage-grouse (Centrocercus urophasianus; hereafter, sage-grouse) and feral horses (Equus ferus caballus) co-occur within Great Basin sagebrush ecosystems of western North America. In recent decades, sage-grouse populations have declined substantially while concomitantly feral horse populations have increased. Although multiple studies have reported feral horses adversely impacting native ungulate species, direct interactions between feral horses and sage-grouse have not been documented previously. We used Bayesian multinomial logistic models to examine the response of breeding male sage-grouse to the presence of native (i.e. mule deer, pronghorn) and non-native (i.e. cattle, feral horses) ungulates on active sage grouse leks (traditional breeding grounds) during 2013-2018. We found sage-grouse were five times more likely to be on active leks concurrent with native ungulates compared to non-native ungulates. Of the four different ungulate species, sage-grouse were least likely to be at leks when feral horses were present. Our results suggest that the presence of feral horses negatively influences sage-grouse lekking activity. Because sage-grouse population growth is sensitive to breeding success, disruption of leks by feral horses could reduce breeding opportunities and limit breeding areas within sage-grouse habitat. Findings are preliminary and provided for timely best science.
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