CONICET | Buscador de Institutos y Recursos Humanos

In this paper, we present our observations on the breeding success and diet of Ferruginous Pygmy-Owls (Glaucidium brasilianum) nesting in northern Argentina. Between 2004 and 2006, we monitored two Ferruginous Pygmy-Owl nests. We removed pellets and prey remains during 2005 and 2006, and estimated consumed biomass of each prey species. We monitored three breeding events. Owls started laying during the second half of October; modal clutch size was 5 eggs (range 4-5 eggs). Hatching success was 80% (4 chicks hatch from 5 incubated eggs) in two of the nests and 50% in the other nest (2 chicks hatch from 4 incubated eggs). All nests were successful and all chicks survived, resulting in 3.3 fledglings per nest. The total nesting period was between 52 and 58 days (28-30 days for incubation and 24-28 days for broodrearing). Fledging occurred between 10 and 20 December. During 90% of nest visits, adults were at the nest tree or neighboring areas, and sometimes they attacked us by flying over and touching our heads. We collected 70 prey items and identified 21 prey species. Birds were the most common prey item (43%), followed by insects (29%), reptiles (16%) and mammals (13%). Creambellied Thrush (Turdus amaurochalinus) was the most common bird prey and represented 11% of the total prey collected, and 27% of the birds collected. Lava lizard (Tropidurus spinulosus) was the most common reptile prey and represented 10% of the total prey collected, and 64% of the reptiles collected. Prey body mass ranged from 12.5 to 225.0 g (mean = 43.7 g, SD = 10.8 g). Birds represented 50% of total biomass, followed by mammals (41%) and reptiles (8%). Further studies to understand the presence of this unusually large prey in their diet should be conducted. Our data suggests that the Ferruginous Pygmy-Owls we studied were generalist predators that fed primarily on birds and arboreal lizards.

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