Welsh Journals

Search over 450 titles and 1.2 million pages

SOME OBSERVATIONS ON THE WINTER DIET OF THE BARN OWL, (Tvtoalba), ON SKOMER ISLAND, DYFED, WALES COLIN W. PLANT. B.Sc. INTRODUCTION In a study of the mammalian prey of the Barn Owl, (Tyto alba), on Skomer Island, off the coast of Pembrokeshire, (now Dyfed), Wales, (Brown and Twigg 1971), demonstrated that in all probability the bird did not make forays in search of food to either the neighbouring mainland of Wales or to the nearby island of Skokholm. In the 119 pellets analysed by these workers, collected in September 1967 and assumed to represent one summer's feeding by the owl, only mammals of the species Clethrionomys glareolus skomerensis, (Skomer Vole), Apodemus sylvaticus, (Field Mouse), and Sorex araneus, (Common Shrew), were represented, in descending order of frequency. No mention was made in this paper to non-mammalian prey species. The opportunity has therefore been welcomed to analyse a further collection of pellets made from the same source in March 1973, representing a part of the winter diet of the Barn Owl. METHODS Broken fragments amounting to 19 pellets, and 27 complete pellets were collected from one of the outhouses of the farm area on Skomer Island. The maximum lengths and diameters of each pellet were obtained using vernier calipers and weights were measured to two decimal places of a gram after three weeks' of air drying at room temperature. The pellets were then dissected dry and the identification of the skeletal remains was checked by reference to Corbett (1964), Southern (1964), and Brown and Twigg (1969), and to a reference collection. The remaining pellet debris was suspended in water, and wet mounts were examined microscopically for the presence or absence of earthworm setae. Avian remains were identified by the British Museum (Natural History), who also confirmed identification of the frog bones and to whom the author expresses his gratitude. RESULTS Weights and measurements of the pellets The ranges and mean values of the maximum lengths and diameters, and of the weights of the 27 complete pellets are presented in Table 1. The weight of the broken pellets was 109.57 gm., which, if divided by the mean pellet weight obtained from the 27 intact pellets, represents 19.85 pellets. This is in good agreement with the visually estimated figure of 19 pellets. Thus, the present results are based on the analysis of a total of 46 pellets.