RESPONSES OF CARIBOU TO OVERFLIGHTS BY LOW-ALTITUDE JET AIRCRAFT

Military training exercises have increased in Alaska in recent years, and the possible effects of low-altitude overflights on wildlife such as barren-ground caribou (Rangifer tarandus) have caused concern among northern residents and resource agencies. We evaluated the effects of overflights by low-altitude, subsonic jet aircraft by U.S. Air Force (USAF) A-10, F-15, and F-16 jets on daily activity and movements of fr ee-ranging female caribou. This study was conducted on caribou of the Delta Caribou Herd in interior Alaska during each of 3 seasons in 1991 : late winter, postcalving, and insect harassment. Noise levels experi enced by caribou were measured with Animal Noise Monitors (ANMs) attac hed to radiocollars. Caribou subjected to overflights in late winter i nterrupted resting bouts and consequently engaged in a greater number of resting bouts than caribou not subjected to overflights (P = 0.05). Caribou subjected to overflights during postcalving were more active (P = 0.03) and moved farther (P = 0.01) than did caribou not subjected to overflights. Caribou subjected to overflights during the insect se ason responded by becoming more active (P = 0.01). Responses of caribo u to aircraft were mild in late winter, intermediate in the insect sea son, and strongest during postcalving. We conclude that females with y oung exhibit the most sensitive response to aircraft disturbance. Acco rdingly, military training exercises should be curtailed in areas wher e caribou are concentrated during calving and postcalving.