Considerations on the structure of the diet of the barn owl (Tyto alba) in sicily (Italy)

Abstract

About 402 of the pellets of the barn owl (Tyto alba), collected throughout the year in open and rural environments in Sicily, contained remains of Microtus savii. This percentage is an exception to the low proportions of Microtidae generally present in the bam owl’s diet in the Mediterranean region. The biometrical study of 666 mandibles of Af. savii taken from 1500 pellets allowed us to determine the monthly trend of the four different size classes, corresponding to age classes of this rodent. Adults and subadults were the most frequent prey; the peaks of juvenile and old adult voles were found respectively in May and September, which suggests an average life of 16 months for the voles. Af. savii was the main component of the diet of the bam owl for eight months of the year, whereas Apodemus sylvaticus was the main component for only two months. This distribution of abundance of the few species preyed on by the barn owl agrees with the Motomura model. The regression of logarithm of occurrence of preys on abundance rank is more sloped if M. savii is at rank 1 than if A. sylvaticus is at the same rank. We found a significant difference between the two slopes. It seems that in Sicily there is a local specialization of the barn owl to prey on M. savii. The daily food intake of this owl was estimated at about 80-85 grams, a value lower than that obtained in North-Europe. © 1987 Taylor & Francis Group, LLC.