Bighorn sheep range from central British Columbia to Baja California. The bighorn group is comprised of the Rocky Mountain bighorn, the California bighorn, and the desert bighorns. This example refers to the Rocky Mountain bighorn, but will apply to the California bighorn. Different methods are appropriate for the desert bighorns of the southwestern US Bighorn sheep usually disperse widely to alpine ranges during summer where census usually is impractical. During this period, older rams are segregated from other sex and age classes. Animals aggregate on rutting ranges during November and December. Aerial census is the most widely used method. Since animals are highly aggregated on spatially confined traditional ranges, total counts rather than sample counts are most commonly used. Topography and flying conditions usually obviate a strictly systemmatic arrangement of flight lines. Therefore, a flight strategy should be planned that will give complete coverage. Although more expensive, helicopters provide greater safety than fixed-wing aircraft.