New study confirms that free-roaming horses have a negative impact on sage grouse

JACKSON, Wyo. – New research from the University of Wyoming suggests that an overabundance of free-roaming Wyoming horses is negatively impacting sage-grouse nesting, breeding and juvenile survival and contributing to the species’ population decline.

In other words, free-roaming horse populations that have exceeded the maximum density for “appropriate management levels” (AMLs) reduce the percentage of sage-grouse nests that successfully hatch and young birds that survive to adulthood. There is no evidence of an effect on adult survival.

The study, published in September in the Journal of Wildlife Management, identifies changing habitat of free-roaming horses, exacerbated by ongoing drought, as a key reason the horses are impacting greater numbers of sage-grouse.

Since the passage of the Wild Free-Roaming Horses and Burros Act of 1971, research has confirmed that the number of free-roaming equids has increased to more than three times the target of 26,785 horses and burros combined for all 177 Herd Management Areas managed by Herd Management Areas, HMAs) has increased the Bureau of Land Management. Free-roaming horse population estimates for each HMA ranged from 59% of AML to seven times the maximum AML.

The research suggests that maintaining the number of free-roaming horses at a “low level of maximum AML” can reduce the further decline of this species, which has already fallen by almost 80% between 1968 and 2023 and by 40 since 2002, according to the US Geological Survey % has decreased.