Free-roaming horses disrupt greater sage-grouse lekking activity in the Great Basin

• Published in: Journal of arid environments 2021-01, Vol.184, p.104304, Article 104304
• Main Authors: Muñoz, Diana A., Coates, Peter S., Ricca, Mark A.
• Format: Article
• Language: English
• Subjects: Cattle; Free-roaming horse; Galliformes; Leks; Mule deer; Pronghorn; Ungulates
• ISSN: 0140-1963; 1095-922X
• DOI: 10.1016/j.jaridenv.2020.104304

Greater Sage-Grouse (Centrocercus urophasianus; hereafter, sage-grouse) and free-roaming horses (Equus caballus) co-occur within large portions of sagebrush ecosystems within the Great Basin of western North America. In recent decades, sage-grouse populations have declined substantially while concomitant free-roaming horse populations have increased drastically. Although multiple studies have reported free-roaming horses adversely impacting native ungulate species, direct interactions between free-roaming horses and sage-grouse have not been documented previously. We compiled sage-grouse lek count data and associated ungulate observations during spring of 2010 and 2013–2018. 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, free-roaming horses) ungulates on active sage-grouse leks (traditional breeding grounds). We found sage-grouse were approximately five times more likely to be present 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 active leks when free-roaming horses were present. Our results indicate that free-roaming horse presence at lek sites negatively influences sage-grouse lekking activity. Because sage-grouse population growth is sensitive to breeding success, disruption of leks by free-roaming horses could reduce breeding opportunities and limit breeding areas within sage-grouse habitat. •Probability of free-roaming horses disrupting sage-grouse lekking activity was >75%.•Horses and cattle disrupted sage-grouse lek activity more than native ungulates.•Presence of non-native ungulates may bias sage-grouse lek counts to be low.•Breeding disruption may impact sage-grouse reproduction and recruitment.