A method for estimating total body weight of avian prey items in the diet of Owls

Abstract

Five bones were measured from 99 birds whose fresh body weight was known, and significant relationships found between the bone measurements and body weights. Measuring bones in owl pellets allows these relationships to be used to estimate likely body weight of avian prey taken by owls. For the passerines, the double log regressions of these skeletal measurements on fresh body weight are given and indicate that the length of the humerus is the most useful basis for estimating body weight of passerines found in owl pellets. This regression is based on 82 specimens of 28 species. A table is given which lists the estimated body weights (with standard errors) obtained using each of the five regressions. Measurements from a small selection of non-passerine skeletons fit these relationships less well but, since the majority of birds taken by most owl species are passerines, the use of the same regressions on non-passerines is unlikely to introduce significant errors into estimates of the weight of birds eaten.