Half of Bighorn Sheep Moved to Kootenai Survived Winter

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Based on spring flights and surveys, Montana FWP Wildlife Biologist Jerry Brown estimates that about half of the 38 bighorn sheep moved to the Kootenai Falls sheep range have survived the winter.

A total of 38 sheep (20 adult ewes, 3 male lambs, 1 female lamb, 14 adult rams) were captured on Wild Horse Island in a net-gun operation and released onto the Kootenai Falls sheep range in two separate transports on January 15 and 16, 2008.

Brown identified five different sheep from the Wild Horse transplant found dead on or adjacent to the sheep range: two were killed by mountain lions, 2 died as winter kills, and one could not be determined. One radio collared ewe died (possible lion kill) and the other two radioed ewes survived the winter.

Brown based his 50 percent overall sheep survival estimate on aerial surveys during the April green-up period. He added that he would continue to monitor the sheep population and the recently transplanted animals into the summer period to determine if more than half of the transplant survived.

The 2007-2008 winter was severe around Libby in the Purcell and Cabinet Mountains, and there was 12-15 inches of snow at the release site at the time of the transplant. Snowfall continued for the next six weeks until there was 28-34 inches of snow at the release site by the end of February. Brown noted that there has not been snow of this magnitude on the Kootenai Falls WMA since the winter of 1996-97. During any of the previous 9 winters, snow depth on the WMA was 6"-12". The transplanted sheep would have had little to no snow to contend with during any of those previous years. Historically, January transplant activities have worked out well.

"Other big game animals in the area suffered this past winter also," said Brown. He noted that low fawn and calf recruitment rates were observed on spring surveys for deer and elk.

Brown said that a few of the recently transplanted sheep have been observed this spring wandering off the sheep range, which is normal for animals introduced into new areas.

The Kootenai Falls bighorn sheep population is the result of a 1954-1955 introduction of 12 and 3 sheep, respectively, all originating from Wild Horse Island in Flathead Lake. These introductions established a viable bighorn population that appeared to peak at about 150-200 animals by the mid 1980’s. The population began showing signs of decline throughout the late 1980’s and early 1990’s, and eventually experienced a drastic reduction in numbers during the 1994-1995 winter. A number of additional sheep introductions followed in 2000, 2003, and 2004. The total of 79 bighorn sheep Brown observed on this spring’s aerial survey was the highest survey sample since the population decline in 1994-95. Brown estimates that he observes about 70 percent of the total sheep population during his aerial survey.

Contact: Jerry Brown, 293-4161.