Accuracy of Aerial Surveys of Waterbird Colonies

Abstract

Ground-truthing surveys were conducted in conjunction with a statewide aerial survey of Florida wading bird colonies to evaluate the efficacy of the aerial technique. Five species, Brown Pelican (Pelecanus occidentalis), Double-crested Cormorant (Phalacrocorax auritus), Anhinga (Anhinga anhinga), Cattle Egret (Bubulcus ibis), and Wood Stork (Mycteria americana), were most often detected during the aerial survey. Most of these species are large birds that tend to nest higher in the canopy or are white-plumaged, and therefore would be expected to be more visible from the air. Five other species, Tricolored Heron (Egretta tricolor), Reddish Egret (E. rufescens), Black-crowned Night Heron (Nycticorax nycticorax), Yellow-crowned Night Heron (Nyctanassa violaceus), and Glossy Ibis (Plegadis falcinellus), were not detected during the aerial survey, presumably because these dark-plumaged species typically nest beneath the tree canopy. Disagreement between aerial and ground survey results also was caused by the inability of the aerial survey to detect some species when they were present in larger colonies or distinguish resting birds from breeding birds. The aerial detection rate of 45 previously unknown colonies was about 71%. Recommendations for improving future aerial surveys of colonial waterbirds include more use of ground surveys for smaller species of day herons and night herons to augment aerial information and smaller width of flight corridors.