Efficiency of aerial surveys of mountain goats

Because managers often rely on aerial surveys to monitor wildlife populatio ns, it is important to estimate the proportion of animals observed. We comp ared the number and age classification of mountain goats (Oreamnos american us) seen during aerial surveys to the actual number of goats in a marked po pulation in west-central Alberta from 1989 to 1999. On average, 69.5% of th e goats were seen during aerial surveys, but the proportion of goats seen i n any one survey ranged from 55 to 84% (CV=12.3%). Observed and actual numb ers of adult goats were best correlated. Yearlings and kids appeared diffic ult to classify from the helicopter; therefore, estimates for these 2 age c lasses were poor. Aerial surveys detected broad population trends over a nu mber of years.