Henry Mountain Bison History
This herd had its roots in Yellowstone National Park. In 1941, the Carbon Emery Wildlife Federation and the Utah State Department of Fish and Game obtained 18 bison, including 3 bulls and 15 cows, in a cooperative effort from the National Park Service. The animals were released near Robber’s Roost Ranch north of the Dirty Devil River on the San Rafael Desert (Nelson 1965). The majority of the animals established themselves near the release site, but a few dispersed to areas north and west, as far away as Ferron and the Strawberry Valley. Most of the dispersing animals were bulls, and it was deemed necessary to supplement the original reintroduction with an additional five bulls the next year. There have been no other introductions into this herd. These bulls joined the majority of the others and crossed the Dirty Devil River in 1942 onto the Burr Desert. These bison used the Burr Desert as winter range and the Henry Mountains as summer range from that time until 1962.
The population had grown to about 71 animals by 1962, when brucellosis was detected in the herd. In 1963, 69 bison were captured in a corral and tested and inoculated for brucellosis. Animals suspected of brucellosis infection were marked, then released and taken by sport hunters. A significant result of the harassment of the capture operation was a change in range used by the bison. Since 1963, the herd has utilized the Henry Mountains as its home range.
Current management practices include an annual helicopter survey, summer ground classification, sport harvest, and extensive habitat management. A population estimate is derived annually based on the number of animals counted during the survey, count conditions, ground classification, the number of animals harvested, and a 5% natural mortality rate.
Pre-season population estimates of the herd, including calves, have ranged from 59 in 1964, to 559 in 1990. The bull:cow ratio has ranged from a low of 37 bulls per 100 cows in 1986, to a high of 72 in 1983 (Table 1). The average from 1949 to 2006 was 53. The number of calves per 100 adults has averaged almost 25 over the same period, ranging from 8 in 2003, to 40 in 1950. The average number of calves per 100 cows has averaged 37, ranging from 17 in 2003, to 56 in 1962.
The average number of estimated adults, post-season, since 1984 has been 266, ranging from a high of 320 in 1990, to a low of 162 in 2005 (Table 2). Currently, the Henry Mountains herd numbers about 340 adults and calves, with a population objective of 275 adults, post-season. Due to drought and poor calf production, the population was in a downward trend, but has responded in recent years to increased precipitation and forage production.
This information has been retrieved from a 2007 report found here: https://wildlife.utah.gov/hunting/biggame/pdf/bison_15.pdf