Factors influencing the survival of Puffins Fratercula arctica at a North Sea colony over a 20-year period

A long-term colour-ringing and resighting programme on the Isle of May, Scotland which involved 734 adult Puffins Fratercula arctica was used to estimate annual survival rates over the period 1973-94 and to investigate some of the factors which influenced survival. Except in 1990 when survival was extremely low, estimated annual survival always exceeded 0.89. There was, however, evidence of a temporal change with survival rates being consistently lower during the second half of the study. This pattern was best described by a stepped model with survival rates of 0.975 (SE 0.004) between 1973 and 1980, 0.924 (0.006) between 1981 and 1994 and a separate value of 0.806 (0.026) for 1990. The decline in survival after 1980 was apparent in all age classes and could not be attributed to a slight change in the study area covered shortly afterwards. There was no evidence that survival rates differed between the sexes but we did find a significant age effect with birds estimated to be 20-25 or more years old either surviving or reproducing much less well than younger individuals.