A method for estimating the number of breeding pairs of great crested grebes podiceps cristatus on lakes

Abstract

This study aimed to find a method for converting counts of adult Great Crested Grebes on lakes to numbers of breeding pairs. Nests and adults were counted during the breeding period in 3 Danish lakes. The study was repeated on one lake the following year. To check the accuracy of the estimates of Needing pairs, counts of broods, with details of brood and chick sizes, were also carried out. The most accurate method for estimating, the number of breeding pairs of Great Crested Grebes from counts of adults is to count birds from the middle of April to the middle of May, just before the start of nest-building, and to halve the maximum number of adults counted. During this period, the count is affected neither by high vegetation nor by adults with unsuccessful breeding attempts moving between the lakes. In large lakes where non-breeding grebes gather, a disadvantage of this method is that it produces overestimates. However, counting Great Crested Grebes in this period can produce reliable estimates of the total adult population of large areas, when counts of adults are carried out ’simultaneously’ covering all possible breeding sites. © Taylor& Francis Group, LLC.