Methods of determining breeding-cliff populations of Guillemots and Razorbills

A CENSUS of cliff-nesting seabirds is usually carried out by making a careful count of every occupied nest, thus giving the number of breeding pairs. This is the most accurate method and can be carried out comparatively easily in the case of species that make a definite nest, e.g., the Gannet (Sula bassana) and the Kittiwake (Rissa tridactyla). Difficulties arise, however, with breeding-cliff colo...