Preliminary data from an aerial population survey conducted by the Bureau of Land Management (BLM) and the U.S. Fish and Wildlife Service (FWS) of northwest Nevada and southern Oregon indicates there is a minimum of 4,200 wild/feral horses within this area, which contains 13 wild horse herd management areas (HMAs), including the five Calico Mountains Complex HMAs, 3 wild horse herd areas (HAs), and two national wildlife refuges.
The BLM and FWS concluded the inventory on June 28 after nine days and approximately 60 hours of flight time using a fixed-wing airplane, which will provide a scientifically-based estimate of the wild/feral horse population. The project area encompasses approximately four million acres of private and Federally-managed public lands.
This improved population survey methodology was developed by the U.S. Geological Survey (USGS) with the assistance of BLM wild horse specialists. The methodology, called Simultaneous Double-Count with Sightability Bias Correction, used three observers to independently observe and record data on groups of individual horses. The methodology incorporates peer-reviewed techniques that have been used for decades to estimate wildlife populations around the world.
A statistician cooperating with USGS will analyze the preliminary data obtained during the inventory flights to provide population estimates with a 95 percent confidence interval. Inventory information relies on the ability of the aerial observers to see horse groups and is strongly dependent on the skill of the individual observer, size of the horse group, and vegetation cover.
The modeling and analysis to be completed will make adjustments to the preliminary data to account for animals not observed during the flight. The simultaneous double-count/sightability bias correction technique will provide more valid population estimates than the standard uncorrected aerial inventory method.
While the BLM does not have a date for the release of the final results of the inventory and necessary modeling work, preliminary data, which represent the minimum number of horses in each area, are shown below. The BLM/FWS will release the results of the analysis to the public when it comes available. The following numbers shown are direct counts of animals seen during the flight and include observed foals of the year.
Bureau of Land Management administered areas:
State/Herd Management Area (HMA) or Herd Area (HA) / Direct Count
- Nevada Calico Complex 5 HMAs
- Black Rock East HMA 69
- Black Rock West HMA 140
- Calico Mountain HMA 436
- Warm Springs Canyon HMA 342
- Granite Mountain HMA 154
- NV/non-HMA areas 136
NV sub-total 1,277
- OR/Beaty’s Butte HMA 377
- OR/Pueblo-Lone Mountain HA 19
- OR/South Catlow HA 0
- OR/non-HMA areas 4
OR sub-total 400
- CA/Bitner HMA 47
- CA/Carter Reservoir HMA 6
- CA/Fox Hog HMA 172
- CA/High Rock Canyon HMA 300
- CA/Massacre Lakes HMA 148
- CA/Nut Mountain HMA 3
- CA/Wall Canyon HMA 87
- CA/New Years Lake HA 100
- CA/non-HMA areas 430
CA sub-total 1,293
US Fish and Wildlife Service administered area:
- USFWS/Sheldon-Hart Mountain 1,247
Inventory Total 4,217
This cooperative effort will establish a base line population count and animal distribution in this large area. Past population surveys and gather operations have shown that wild/feral horses may move among a number of HMAs and the Sheldon and Hart Mountain National Wildlife Refuges.
This population survey represents a point in time and that because of the free-roaming nature of the animals their movement between HMAs is normal and expected. While the total number of animals is expected to remain stable until next year’s foaling season, the numbers within each HMA will vary over time.
Pre-determined transects spaced 1 ½ miles apart were flown at an altitude of approximately 500 feet above ground level and speeds ranging between 95 and 110 nautical mph. Data collected included the number of horses per group, type of topography, plant cover, activity of the horses, and other parameters that will be used to develop population estimates. All observed horse groups also had their locations recorded via GPS. BLM and FWS are planning to return to the area later this fall for a second survey that will provide information on the herd movement and how that can affect population counts in the individual areas.