Modeling elk sightability bias of aerial surveys during winter in the central Cascades

Aerial surveys of elk have generally not been used to estimate elk abundance in western Washington primarily due to concerns over the highly variable delectability of elk in forested vegetation. The purpose of our study was to investigate the development and application of aerial sightability models to survey elk in forested habitats of the west-central Cascades. Survey units were delineated and surveyed from a helicopter. We used radio-tagged elk and logistic regression to model the influence of vegetation cover characteristics, elk group size, and activity on sightability of elk. Models were assessed using Akaike Information Criteria. The best model included elk group size and percentage of vegetative cover. These results indicate that when corrected for sightability, aerial surveys for elk may be a reasonable alternative for assessing elk abundance in wintering elk herds of the central Cascades.