28-YEAR STUDY OF BREEDING FULMARS FULMARUS-GLACIALIS IN ORKNEY

Colour‐ringed breeding Fulmars were studied on the island of Eynhallow, Orkney, from 1950 onwards. During the 28 years, there was an average increase in population size of about 4% (9 birds) per annum, standard deviation 23%, The mean population size was 161 birds, with about 22 new breeders and 26 new nest sites per annum. There were marked fluctuations in numbers of birds and occupied sites per annum, causing deviations from the underlying trend. Most nest sites were on the coast. The distribution of occupied nests was variable, the most favoured areas changing over the years. A mean of 46 chicks fledged per annum. The proportion of breeding pairs which fledged a chick varied from 16 to 52% (even though there was no known change in conditions). Success in small areas sometimes differed considerably from that of the island as a whole. Although most fledglings were ringed, only 3% have returned and bred on Eynhallow. Between 89 and 94% of those which survived to breeding age must have bred elsewhere. It was concluded that the population size and breeding success of small areas could differ quite markedly from that on a wider scale and could vary quite markedly over the years, facts that have important implications for monitoring of seabird colonies. Copyright © 1979, Wiley Blackwell. All rights reserved