Efficiency of aerial surveys of mountain goats

Because managers often rely on aerial surveys to monitor wildlife populations, it is important to estimate the proportion of animals observed. We compared the number and age classification of mountain goats (Oreamnos americanus) seen during aerial surveys to the actual number of goats in a marked population in west-central Alberta from 1989 to 1999. On average, 69.5% of the goats were seen during aerial surveys, but the proportion of goats seen in any one survey ranged from 55 to 84% (CV = 12.3%). Observed and actual numbers of adult goats were best correlated. Yearlings and kids appeared difficult to classify from the helicopter; therefore, estimates for these 2 age classes were poor. Aerial surveys detected broad population trends over a number of years.