DIET OF SHORT-EARED OWLS ASIO FLAMMEUS OVER SEVEN WINTERS IN COUNTY CORK, IRELAND

Abstract

Previous studies of short-eared owl Asio flammeus (Pontoppidan) diet in Ireland have all been relatively small in scale and restricted in time. A total of 759 prey items were recovered and identified for this study during six winters (2005/2006-2010/2011). A further 271 prey items collected by the same authors in 2004/2005 for a previous study makes this the largest body of work on the prey of short-eared owls carried out in Ireland to date at 1030 prey items. Bird prey made up 55.9% by number and 83.1% by weight, and mammal prey made up 42.4% by number and 16.9% by weight. Thirteen invertebrates were also recovered. Dunlin Calidris alpina (L.) was the most frequently taken bird species, followed by snipe Gallinago gallinago (L.) and redshank Tringa totanus (L.). Together, these three wading birds formed 62.2% of prey by weight. Passerine birds were also taken, but only the thrush family (Turdus spp), collectively, was of any importance at 10.1% of prey by weight. The wood mouse Apodemus sylvaticus (L.) was the most frequently taken mammal species (8.2% by weight), while smaller numbers of other rodents and shrews were taken. Dunlin was an important prey species up to February, but declined thereafter, while snipe and redshank remained important throughout the winter. Passerine birds were also taken throughout the period, but their overall contribution was lower than that of wading birds. Brown rats Rattus norvégiens (Berkenhout) and small mammals were taken throughout, but their monthly contribution was generally below 20%, except for one occasion in April in one year. Chi-square tests showed significant differences in some prey species and categories between months and years. While the reasons for some of the differences remain unknown, others are related to prey numbers available in any given month. There is also a suggestion that the severe winter of 2010/2011 influenced the higher than expected number of dunlin, and the lower than expected number of small mammals taken as prey in that winter.