JACKSON, Wyo. — New research from the University of Wyoming suggests an overabundance of free-roaming Wyoming horses negatively impact nest, brood and juvenile survival of greater sage grouse and contribute to the species’ population declines.
In other words, free-roaming horse populations that have exceeded the maximum densities for “appropriate management levels” (AMLs) are reducing the percentage of sage grouse nests successfully hatching and young birds surviving to adulthood. There is no evidence of an effect on adult survival.
The research, which was published in September in The Journal of Wildlife Management, identifies free-roaming horse habitat alteration, exacerbated by ongoing drought, as the primary reason the horses are impacting greater sage grouse numbers.
Since the passage of the Wild Free-Roaming Horses and Burros Act of 1971, research confirms free-roaming equid numbers have increased to over three times the targeted goal of 26,785 horses and burros combined for all 177 designated herd management areas (HMAs) managed by the Bureau of Land Management. Population estimates of free-roaming horses for each HMA ranged from 59% of the AMLs to 7 times the maximum AML.
The research suggests that maintaining free-roaming horse numbers at “low levels of maximum AML” can reduce further declines of this species that already declined nearly 80% between 1968 and 2023 and 40% since 2002, according to the U.S. Geological Survey.
