Estimating fresh mass of small mammals in owl diet from cranial measurements in pellets remains

Canova L., Yingmei Z. & Fasola M.


Owl diet is commonly studied through pellet analysis, and it is usually described as prey frequency or biomass. However, frequency does not indicate the relative trophic importance of prey. Biomass estimates, based on mean mass data from the general literature, do not take into account size, sex and geographical variations. We suggest a regression method for better estimating individual mass from cranial bones and mandibles of small mammals, and we provide regressions for 6 species, frequently preyed upon by owls in Italy. For each prey species, at least one variable explained a significant proportion of sample variation and was significantly related to the mass. The bone length-fresh mass relationship is useful only when well-preserved bones are available. Usually, cranial bones in pellets are severely damaged and the number of feasible measurements is limited, therefore multiple regression methods based on several variables are of limited use.