Owls of the genus Glaucidium (pygmy-owls and owlets) are small, crepuscular and diurnal, cavity-nesters. Although 10 pygmy-owl species occur in South America (König & Weick 2005), only one species, the Austral Pygmy-Owl (Glaucidium nanum) had a detailed dietary study (Jiménez & Jaksic 1989), and only anecdotal reports exist for the diet of some of the other species (Poulin et al. 1994, Robbins & Stiles 1999). The Ferruginous Pygmy-Owl (Glaucidium brasilianum) is geographically widespread, with 3 of 12 subspecies occurring in Central and North America (Holt et al. 1999). In Argentina, it occurs in a wide array of subtropical ecosistems that range from semiarid desert to rain forest (Mazar Barnett & Pearman 2001). In this paper, we present our observations on the breeding success and diet of of Ferruginous Pygmy-Owls nesting in northern Argentina.

The study site was a subtropical dry-forest (El Impenetrable, 160 m asl) of the “Gran Chaco” ecoregion in northern Argentina, with seasonal precipitation mostly occurring between October and February. Mean annual precipitation and temperature were 60 cm and 23 C, respectively. The dominant tree species include white quebracho (Aspidosperma quebracho-blanco) and the red quebracho (Schinopsis lorentzii; Burkart 1999). Between 2004 and 2006, we found two Ferruginous Pygmy-Owl nests in cavities in white quebracho trees, 5.4 m and 6.0 m above ground level, and 40 cm and 93 cm depth, respectively. Coordinates of nests were for nest 1, 25 30’05” S, 61 54’49” W, and for nest