Results from this summer’s bighorn sheep survey indicate the population in western North Dakota is lower than last year.
State Game and Fish Department big game biologist Brett Wiedmann said the July-August survey showed a minimum of 287 bighorn sheep, down 4 percent from 2013. Results revealed 82 rams, 153 ewes and 52 lambs.
Due to an ongoing disease event in the northern badlands, Game and Fish biologists have verified more than 20 bighorn sheep deaths over the summer. Wiedmann said the survey is a tale of two segments of the state’s population. “The four herds in the northern badlands not affected by the die-off increased 28 percent from last year, with the lamb count increasing 46 percent,” Wiedmann said. “However, the eight herds impacted by disease declined 25 percent, with the lamb count declining by 66 percent.”
Although population levels were down markedly in portions of the northern badlands, biologists were pleased to see a slight increase in the southern badlands.
The department’s survey does not include approximately 40 bighorn sheep that live in the North Unit of Theodore Roosevelt National Park.
Game and Fish wildlife veterinarian Dan Grove said only time will tell how severe the die-off will be. “Mortalities so far have been significant but not yet catastrophic,” Grove said. “However, the outbreak is ongoing, and we have detected a virulent strain of bacteria from biological samples collected from dead bighorns. Consequently, impacts will be more apparent when females and lambs are recounted next March, but the full extent of the outbreak likely will not be realized until the 2015 survey is completed.”
Each summer, Game and Fish Department biologists count and classify all bighorn sheep, a process that takes nearly six weeks to complete as biologists locate each bighorn herd in the badlands by tracking radio-marked animals from an airplane, and then hike into each group to record demographic data using a spotting scope and binoculars. Biologists then complete the annual survey by recounting lambs in March to determine lamb recruitment, or lambs that survive the first winter.