Testing a double-count aerial survey technique for white-tailed deer, Odocoileus virginianus, in Québec

Abstract

In a double-count aerial survey, two independent observers, located on the same side of an aircraft, simultaneously count animals in sample plots. To evaluate if this technique could be implemented as part of our White-Tailed Deer (Odocoileus virginianus) management program, we assessed its precision to estimate densities over large wintering areas (≥ 25 km2, 10 surveys) and whole hunting zones (1600-26 000 km2, 14 surveys). We also tested its repeatability by replicating eight surveys two to five times. We finally compared double-count aerial surveys with pellet-group counts, which were previously used to estimate deer numbers. Surveys of large wintering areas indicated that a 90% confidence interval (CI) of ± 20% could be obtained with a sample size of 50-100 plots (5 km × 60 m strip plots). In hunting zones, 100-200 plots would have been needed to reach the same precision. Densities from replicated surveys were not considered biologically different (difference > 30% between two replicates within each survey) for 21 of 24 replicates overall. When both techniques were applied to the same wintering areas, the 90% confidence limits of the aerial estimate encompassed the pellet-group estimate in five of nine surveys, and was lower in one survey and was higher in three surveys. Although the costs of the aerial survey and the pellet-group count techniques are rather similar, we suggest that aerial surveys provide better estimates. We conclude that the double-count technique is reliable to survey White-Tailed Deer at a reasonable cost. In our context, a typical zone (200 plots) requires 30-40 helicopter hours and 10 days of work by a three-person crew.