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 use d to estimate annual survival rates over the period 1973-94 and to inv estigate some of the factors which influenced survival. Except in 1990 when survival was extremely low, estimated annual survival always exc eeded 0.89. There was, however, evidence of a temporal change with sur vival rates being consistently lower during the second half of the stu dy. This pattern was best described by a stepped model with survival r ates 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 decl ine in survival after 1980 was apparent in all age classes and could n ot 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 estimat ed to be 20-25 or more years old either surviving or reproducing much less well than younger individuals.