VISIBILITY BIAS OF WATERFOWL BROOD SURVEYS USING HELICOPTERS IN THE GREAT CLAY BELT OF NORTHERN ONTARIO

Replicate helicopter surveys were employed to examine the efficiency o f helicopter-based waterfowl brood surveys in the Great Clay Belt regi on of northern Ontario during 1990. Waterfowl broods were resighted mo re often on lake-estuary and lake-shore marshes than on other boreal f orest wetland types. Low brood resighting (<40%) on most boreal forest wetland types indicate that a considerable number of broods are misse d during helicopter surveys. Differences in resightability were not de tected between divers and dabblers. The visibility correcton factor fo r broods on all wetlands combined was 2.09. Helicopter surveys in the boreal forest should be accompanied by a replicate survey to improve t he precision of the waterfowl brood density estimate and establish a v isibility correction factor.