VULNERABILITY OF SCOTTISH SEABIRDS TO OFFSHORE WIND

2.3 Adult survival rate

Published data on adult survival rate were used as a measure of the position of each species on the'r-K continuum' which reflects the vulnerability of species to any increase in mortality above natural mortality (species with low adult survival rates tending to have early age of first breeding and high reproductive output and so be less vulnerable to additional mortality than the extreme 'k-selected' species). Data were taken from Garthe and H◘ppop (2004) for the species listed in that paper. Where species were not listed in Garthe and H◘ppop (2004), data were taken from Saether (1989), from del Hoyo et al. (1992, 1996), from Glutz von Blotzheim and Bauer (1982), from individual species studies, or estimated from data for closely related species ( Table 1). Where several estimates were available, preference was given to more recent studies, and studies in the UK rather than from other parts of the world, since survival rates in populations of the same species may sometimes differ between geographical regions, as is particularly evident for example for black-legged kittiwakes in the Pacific and Atlantic (Hatch et al. 1993). For example, the estimated adult survival rate of common eiders in Denmark was 0.8 (Paludan 1962, cited in Cramp and Simmons 1977) but there is a high hunting mortality in that country. In contrast, the common eider is protected in the UK and the survival estimate of Krementz et al. 1997 of 0.895 seems more appropriate ( Table 1).

Adult survival rates were classified on a 1 to 5 scale following the banding used by Garthe and H◘ppop (2004): 1 (adult survival less than 0.749), 2 (adult survival 0.75-0.799), 3 (0.80-0.849), 4 (0.85-0.899), 5 (adult survival above 0.90).

Table 1. Estimates of breeding and winter (or passage) population sizes in Scotland (add data from Forrester et al. 2007), and adult survival rates of seabirds from the literature, or estimated from related species where not directly available.