Statistical analysis for 2026 survey of burro abundance in Tassi-Gold Butte Herd Management Area (HMA) and surrounding lands in Grand Canyon-Parashant National Monument (GCPNM), AZ

In January 2026, Bureau of Land Management (BLM) personnel conducted simultaneous double-observer aerial surveys of the wild burro populations in the Tassi-Gold Butte Herd Management Area (HMA) in the Grand Canyon-Parashant National Monument (GCPNM), and nearby lands surrounding the HMA. The HMA and the entire survey area falls completely within GCPNM. Both GCPNM and the HMA are jointly managed by the BLM and National Park Service.

Surveys were conducted using methods recommended by BLM policy and the National Academy of Sciences with detailed methods. These data were analyzed to estimate sighting probabilities for wild burros, with sighting probabilities then used to correct the raw counts for systematic biases (undercounts) that are known to occur in aerial surveys, and to provide confidence intervals (which are measures of uncertainty) associated with the abundance estimates. However, other studies indicate that even such estimates are at least 25% lower than true burro herd size.