Suggestions have been made for sexing Great Grey Owls Strix nebulosa using body measurements as criterion. Here we present measurement data from a long-term collection of 83 dead owls from western and northern Finland indicating that lengths of forearm, and claws 1, 2 and 4, are superior over traditional measurements of wing, tarsus, bill and body mass in determining sex of Great Grey Owls. Forearm of males ranged 123–148 mm, and was on average 138 mm (n = 31). In comparison, the forearm of females ranged 131–162 mm, with an average of 147 mm (n = 49). Based on a logistic regression analysis, the combination of forearm, second claw and wing length was the best predictor in correct sex determination of 95% of the Great Grey Owl specimens.
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