Dieta anual del lechuzÓn orejudo (asio clamator) en el lÍmite austral de su distribuciÓn

Abstract

The Striped Owl (Asio clamator) is a nocturnal raptor that inhabits open and forested habitats of the Neotropical region. This species has been characterized as a specialized predator of birds and mammals in different areas of its distribution range, although most studies are based on local, short-term records of prey consumed. In this study, we investigated the diet of A. clamator along the year in the southeast of the Pampas region of Argentina, which corresponds to the southernmost boundary of the species distribution range. We analyzed 126 pellets collected between February 2005 and March 2006 in a forest of Celtis tala. We calculated numeric and biomass frequencies of each prey item and the food-niche breadth, and compared diet composition among periods (breeding and non-breeding) using Kendall's Coefficient of Concordance. The diet of A. clamator was dominated by mammals in terms of numeric (78.5% of total prey) and biomass frequencies (93.1% of total biomass), followed in order of importance by birds (21.5% of total prey). Rodents were the most important prey among mammals, particularly Rattus spp., whereas among birds the most important prey was Myiopsitta monachus, representing the first record of consumption of parrots by this raptor. Food-niche breadth showed moderate to low values for the whole period. We did not detect differences in diet composition between the different periods. Our results indicate that, at the southernmost boundary of its distribution range, A. clamator behaves as a specialized predator of vertebrates throughout the year, in agreement with reports from other areas regarding the importance of big-sized prey (> 100 g) in the diet of this species.