Habitat patch size and local distribution of borrowing owls (Athene cunicularia) in Argentina

DIEGO VILLARREAL; MARCELA MACHICOTE; LYN C. BRANCH; JUAN JOSÉ MARTINEZ; ANALÍA GOPAR

ORNITOLOGIA NEOTROPICAL

Año: 2005 vol. 16 p. 529 - 537

1075-4377

Abstract. – Habitat quality and landscape structure are key factors that determine the distributions of animals. The general characteristics of the habitat of Burrowing Owls (Athene cunicularia) have been well studied, but little is known about how landscape structure affects this species. Other studies have suggested that food resources for owls should be higher in small patches because of increased edge and proximity to dense vegetation, and predation risk should be lower in large patches. We examined the relationship between patch occupancy by owls and the size of habitat patches produced by grazing of colonial, burrowing rodents, plains vizcachas (Lagostomus maximus, Chinchillidae), in central Argentina. We investigated the hypothesis that patch size influences prey availability for owls by comparing arthropod abundance in habitat patches of different sizes. We also examined the relationship between habitat patch size and vegetation characteristics of the patch. Vizcacha colonies occupied by owls had significantly smaller grazed areas than unoccupied colonies. Abundance and biomass of arthropods were not different among patch sizes or between grazed and ungrazed areas, suggesting that owls are not choosing small patches because they have more arthropods as food resources. Association of owls with small colonies may be explained by an inverse relationship between patch size and habitat quality, with low quality linked to high shrub cover. Additional studies are required to test this hypothesis and to elucidate the role of mammals, in general, in providing habitat for Burrowing Owls in South America.