Small mammals in the diet of barn owls, Tyto alba (Aves: Strigiformes) along the mid-Araguaia river in central Brazil

Rita G. Rocha,Carlos Fonseca,Yuri L.R. Leite,Eduardo Ferreira,Leonora P. Costa

doi:10.1590/s1984-46702011000600003

Abstract

We collected and analyzed 286 Barn owl, Tyto alba (Scopoli, 1769), pellets from two nests in different environments along the mid-Araguaia River in central Brazil. Our analyses revealed that these owls feed mainly on small mammals, especially rodents. Owls from the riverbanks at Fazenda Santa Fé had a more diverse diet, preying mainly on rodents that typically inhabit riparian grasslands - Holochilus sciureus Wagner, 1842 - and forests - Hylaeamys megacephalus (Fischer, 1814) and Oecomys spp., which probably also occur in forest borders or clearings. On the other hand, owls from an agroecosystem at Fazenda Lago Verde preyed mostly on rodent species common in these agrarian fields, Calomys tocantinsi Bonvicino, Lima & Almeida, 2003. Additionally, we compared small mammal richness estimates based on the analysis of owl pellets with estimates from live-trapping in the same areas. Owl pellets revealed two rodent species undetected by live traps - Euryoryzomys sp. and Rattus rattus (Linnaeus, 1758) - and four rodent species were trapped, but not found in owl pellets - Oecomys roberti Thomas, 1904, Pseudoryzomys simplex (Winge, 1887), Rhipidomys ipukensis Rocha, B.M.A. Costa & L.P. Costa, 2011, and Makalata didelphoides (Desmarest, 1817). Traps yielded higher species richness, but these two methods complement each other for surveying small rodents.

Highlights

The Barn owl, Tyto alba (Scopoli, 1769), is a nearly cosmopolitan owl that inhabits mostly open areas, including farms, grasslands and woods (MIKKOLA 1995, SICK 1997, VENABLE 1997)
Owls regurgitate prey remains in the form of pellets, which have been studied to understand their feeding habits (e.g., BELLOCQ 1990, SCHEIBLER & CHRISTOFF 2004, TREJO & LAMBERTUCCI 2007), and as a method for inventorying small mammals (e.g., BONVICINO & BEZERRA 2003, TORRE et al 2004, SOUZA et al 2010, TETA et al 2010)
When compared with the 142 studies of Barn Owl pellets in Argentina, very few studies were focused on this subject in Brazil (e.g. ESCARLATE-TAVARES & PESSÔA 2005, RODA 2006, SCHEIBLER & CHRISTOFF 2004, 2007, BUENO & MOTTA-JÚNIOR 2008, SOUZA et al 2010), and only three were carried out in central Brazil (MOTTA-JÚNIOR & TALAMONI 1996, JORDÃO et al 1997, BONVICINO & BEZERRA 2003)

Summary

Introduction

The Barn owl, Tyto alba (Scopoli, 1769), is a nearly cosmopolitan owl that inhabits mostly open areas, including farms, grasslands and woods (MIKKOLA 1995, SICK 1997, VENABLE 1997). Owls are specialized predators and have very large eyes, which allow vision in limited light, and an acute hearing. These characteristics make them well adapted for hunting at night (VENABLE 1997). Owls regurgitate prey remains in the form of pellets, which have been studied to understand their feeding habits (e.g., BELLOCQ 1990, SCHEIBLER & CHRISTOFF 2004, TREJO & LAMBERTUCCI 2007), and as a method for inventorying small mammals (e.g., BONVICINO & BEZERRA 2003, TORRE et al 2004, SOUZA et al 2010, TETA et al 2010). The aims of this study are: 1) to compare the species composition of small mammals consumed by Barn owls in two different environments within an ecotonal region between Cerrado and Amazonia, in central Brazil, and 2) to compare the estimates of small mammal richness obtained from these pellets with a concomitant small mammal inventory using live-traps in the same areas

Objectives

Methods

Results