Estimating the population size of breeding Greylag Geese Anser anser based on vertical aerial photographs

Abstract

Due to the unreliability of estimating the breeding population of Greylag Geese using ground counts at the nature reserve of Vejlerne, Denmark, vertical aerial photographs were taken in 1994 to estimate the number of nests and incubating geese. Reliability (based on ground truthing) of nest identification from the images was found to be 97% correct. This gave a total population of 713 nest in the whole reserve compared to 831 (maximum) and 623 (minimum) pairs based on ground counts. The vertical aerial photographs provided excellent images of the incubating geese in homogeneous reedbeds, as occur at Vejlerne. The method is valuable for the long-term monitoring of breeding Greylag Geese in reedbeds due to the precise location of nests.