Diving speed and food-size selection in common guillemots, Uria aalgae

Abstract

Results of choice experiments showed that guillemots Uria aalge prefer sprats Sprattus sprattus of a body depth of 16 to 17 mm. This is notably smaller than the maximum size that guillemots are able to swallow (body depth about 44 mm). A small proportion of the selected fish was used for display on the breeding ledge; these were significantly bigger than those preferred for consumption. Mean velocity during horizontal underwater flight was 2.18 m·s −1, with the maximum recorded being 2.57 m·s −1. This is considerably faster than the speed of any prey.