Cause Specific Mortality of Desert Bighorn Sheep Lambs in the Fra Cristobal Mountains, New Mexico, Usa

Bighorn sheep (Ovis canadensis) herds have suffered recent declines across their previous range, and desert bighorn sheep (O. c. mexicana) are listed as an endangered species in New Mexico. One factor affecting growth rates of these populations is low and variable lamb recruitment. Capturing and radio-collaring lambs can provide opportunities for collecting valuable information on factors potentially affecting long term population persistence. Little information is available on cause-specific lamb mortality or on methods for obtaining such data. We tested 3 different capture techniques on desert bighorn sheep lambs. We captured lambs during the spring lambing seasons of 2001 and 2002 by approaching lambs on foot and restraining them by hand, jumping from a helicopter and restraining them by hand, and firing a net-gun from a helicopter. We captured 6 lambs by hand on the ground, 4 lambs by hand from a helicopter, and 11 lambs from a helicopter with a shoulder-mounted or skid-mounted net-gun. The best capture technique depended on the specific circumstances of each different situation. Since we were concerned with sample size considerations, our success depended on the implementation of all 3 techniques. However, the hand-capture technique allowed us to capture very young lambs that we would not have attempted to capture with either helicopter technique due to stress, risk of injury, and cost. This technique may be applicable to other ungulate populations. 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38