New records on the distribution of three rodent species in NE Portugal from barn owl (Tyto alba) diet analysis

Abstract

100 In Portugal some information has been published about the spatial distribution, at a local or regional scale, for several small mammal species (e.g. Madureira & Magalhaes 1980, Magalhaes & Madureira 1980, Tome 1994, Cruz et al. 2002, Roque 2003, Temme 2003, Vale-Goncalves 2006, Godinho 2007, Mira et al. 2008, Santos et al. 2009, Rosalino et al. 2010, Machado 2011, Pauperio 2012, Garrido-Garcia et al. 2013). Nevertheless, in the absence of a national mammal atlas, the knowledge of small mammals distribution in Portugal is still very incomplete. The data available in the reference guide of terrestrial mammals of Portugal (Mathias et al. 1999) exhibit significant geographical gaps, since the information provided was based on data collected in 90 s of last century and the presence of the species are represented in a grid of 50x50 km cells. Therefore, this reference work needs to be updated and complemented with new records in order to best understand the spatial distribution patterns of small mammals. In this perspective, the present study aims to contribute for the knowledge upgrade on the small mammals’ distribution in northeastern Portugal (Fig. 1) through a regional intensive sampling network and by using the standard indirect method of the barn owl pellets analysis. The barn owl Tyto alba (Scopoli, 1769) is a nocturnal bird of prey that feeds mainly on small mammals, although birds, bats, reptiles, amphibians, insects and fishes can constitute an alternative prey (Mikkola 1983, Cramp 1985, Taylor 1994, Roulin & Dubey 2012, Roulin & Dubey 2013). Barn owl pellet analysis is an extremely valuable tool for the characterization of small mammal communities and is widely used to study their richness and composition, providing data that are difficult or impossible to detect otherwise, namely regarding the presence of less common prey species, the predator pressure, and seasonal differences in the owl s diet (Taylor 1994, Torre et al. 2004, Yalden 2009). The presence of small mammals in barn owl pellets was assumed to be related with a year-around prey availability in the surrounding areas of their nest and/or roost sites (Taylor 1994). Therefore, potential nest and roost sites were searched in the study area to detect the presence of barn owls. Indirect evidences of the species occurrence (e.g. pellets, feathers, white droppings near nests or roost sites) were considered as showing site/nest occupation and included in the experimental design as potential sampling point. The small mammal communities and their distribution was assessed by the analysis of 2,116 pellets collected, between 2006 and 2011, in 23 sites/nests located in the districts of Vila Real, New records on the distribution of three rodent species in NE Portugal from barn owl (Tyto alba) diet analysis