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WSF Grant-in-Aid Update - Hart Mountain National Antelope Refuge California Bighorn Sheep Recovery (OR)

February 15, 2023

California bighorn sheep (BHS), an iconic species native to Oregon and the Hart Mountain National Antelope Refuge (NAR), were extirpated from Oregon by 1912. The species was successfully reintroduced in 1954 when 20 sheep were translocated to the NAR from Williams Lake, British Columbia. After re-introduction and establishment, the NAR herd was robust enough to translocate bighorn sheep to other areas in and around Oregon.

Hart Mountain NAR, in southeastern Oregon, is 100 percent public land managed by the U.S. Fish & Wildlife Service. Since 2017, wild sheep on Hart Mountain NAR have decreased significantly, from more than 150 to fewer than 50. Without prompt intervention and management action, this herd was at risk of extirpation. In 2022, the Hart Mountain BHS Management Plan and Environmental Impact Study (EIS) was developed and adopted to identify management actions to aid the recovery of this herd. An integrated management approach focusing on short-term predator control (mountain lions) and longer-term habitat management actions (juniper control and water sources) has been launched to benefit, recover, and support a sustainable herd.

Data collected over the last 20 years and across multiple collaring events documented cougars as a significant and primary predator of adult bighorn sheep on the NAR. Of 19 sheep fitted with radio collars on the NAR in January 2019, seven of 10 (70%) documented deaths were likely attributed to cougar predation. In 2019 (May–October) and 2020 (May–September), hair snares and camera traps indicated 12-16 individual cougars were patrolling the bighorn sheep habitat on Hart Mountain NAR. During a 4-year study (2004-2008) on the NAR, researchers found cougar predation or probable cougar predation accounted for 63% of the mortalities. High cougar predation coupled with no indication of disease in live sheep led researchers/managers to conclude that disease was not a substantial mortality factor, and that cougar management would benefit this herd the most.

Following adoption of the Hart Mountain BHS Management Plan and EIS, the NAR initiated cougar removals in 2022. The NAR entered a contractual agreement with USDA-APHIS-Wildlife Services for professional, administrative, lethal removal of cougars only in the established BHS-Cougar Management Zone; removals are NOT intended to eliminate cougars from the NAR.

The intent of cougar removal is to decrease bighorn sheep adult mortality and increase lamb survival and recruitment. Wildlife Services agents (trappers/dog handlers) using trained hounds, snares, and/or calls conduct removals from August 1 to March 31, concurrent with existing Refuge hunting seasons and when conditions were likely to be more successful. The primary method is using trained hounds to trail and locate specific individual cougars, which are then euthanized by gunshot. Hounds are preferred because this is typically the most effective and selective method of capturing cougars with the lowest potential to affect non-target animals; however, because of inaccessible terrain, solely using dogs would be impractical. The NAR provided $100,000 to fund the first two years of the agreement with USDA-APHIS Wildlife Services. However, subsequent years were unfunded.

The Wild Sheep Foundation committed $100,000 in Grant-in-Aid (GIA) support for this project; WSF secured $5,000 in partnership funding from the Pope & Young Club. In addition, WSF obtained a $10,000 commitment from the Oregon Wildlife Foundation. The USFWS contributed another $165,000 toward this current project, in addition to their previous $100,000 contract with USDA-APHIS-Wildlife Services.

On January 20, 2023, ODFW & USFWS personnel, with excellent net-gun capture work done by Baker Aircraft, were able to capture, collar, and sample six ewes and four rams on Hart Mountain NAR. These collared bighorns will be monitored to evaluate survival/predation risk, determine seasonal and daily movements and habitat use; biological samples collected will be analyzed to assess pathogen risk and disease/health status of bighorn sheep on Hart Mountain NAR.

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