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Yellowstone elk survey reveals low calf survival

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A bull elk searches for food beneath the snow in Yellowstone National Park. NPS PHOTO

MONTANA DEPARTMENT OF FISH, WILDLIFE AND PARKS

Elk numbers in Yellowstone National Park’s northern herd are fewer compared to last year, however the population remains above the 10-year average and other recent counts. Low calf survival will likely impact the population over the next two years, according to a population survey conducted last month.

The Northern Yellowstone Cooperative Wildlife Working Group, which consists of staff from the Montana Department of Fish, Wildlife and Parks, National Park Service, U.S. Forest Service and U.S. Geological Survey-Northern Rocky Mountain Science Center, conducted its annual late winter classification of the northern Yellowstone elk population on March 17-19.

All observed elk were counted across the survey area, and when possible, staff also classified elk by age and sex. This survey was conducted consistently with the 2016 classification survey in order to assess population changes over the past three years. Survey conditions were favorable across the region; however, winter conditions were severe, and many elk were observed to be in poor condition.

Staff counted 5,800 elk total, which included 1,361 elk, or 23.5 percent, inside Yellowstone National Park and 4,149 elk, or 71.5 percent, north of the park. The total count was 23 percent lower than the 7,579 elk observed during the 2018 trend count, and 23 percent lower than the 7,510 total elk counted during the 2016 classification survey, but higher than the 10-year average count of 5,399 elk. The long-term average of observed elk numbers since surveys began in 1976 is 10,634 elk, with a peak-high count of 19,045 elk in 1994 and a low count of 3,915 in 2013.

Of the 5,800 elk counted, staff classified 5,510 elk by age and sex, resulting in ratios of 15.2 calves, 5.2 yearling bulls and 12.6 brow-tined bulls per 100 cows. Calf and yearling bull ratios were lower than recent surveys and long-term averages. Brow-tined bull ratios were higher than recent surveys, but below long-term average. Staff observed 16 percent fewer cows, 46 percent fewer calves and 42 percent fewer yearling bulls as compared to the 2016 classification survey. Brow-tined bull numbers increased by 21.3 percent from 432 observed in 2016 to 524 observed in 2019.

This is the second consecutive year with calf ratios below the threshold of 20 calves per 100 cows considered necessary to maintain a stable population. It’s likely that additional winter mortalities will occur into spring, further reducing overall numbers and recruitment. Below-average yearling bull and calf recruitment is likely to result in lower numbers of brow-tined bulls being recruited into the population over the next two years.

Though overall elk numbers are down this year as compared to 2018, it’s not unusual to observe fluctuations in numbers of elk counted due to survey quality, elk movements and sight-ability of elk, which vary with conditions. Trends in elk populations are best assessed by considering multiple years of survey data together. The trend for this population has been increasing since 2013; this is the first year since 2013 that elk numbers have fallen from the previous year. The working group will continue to monitor trends of the northern Yellowstone elk population and evaluate the relative contribution of various components of mortality, including predation, environmental factors and hunting.

The working group was formed in 1974 to cooperatively preserve and protect the long-term integrity oft he northern Yellowstone winter range for wildlife species by increasing our scientific knowledge of the species and their habitats, promoting prudent land management activities, and encouraging an interagency approach to answering questions and solving problems.

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