Breeding density and success, and diet composition of Little Owls Athene noctua in steppe-like habitats in Portugal

Abstract

We studied the breeding density and success, and diet composition of Little Owls Athene noctua during 1997-1999 in a treeless pseudo-steppe and open woodland in Portugal. Breeding density was higher in the woodland area (7.0 pairs/km 2) than in the pseudo-steppe (2.5 pairs/ km 2), probably due to greater availability of potential nest-sites. In the woodland, the number of owl pairs was higher in areas with intermediate tree density. The overall breeding success (yearly mean: 0.61-2.26 fledglings) and the proportion of vertebrates in the diet (1.5% of prey number) were lower than those in most studies in Central and Southern Europe. The overall breeding success per pair was higher in the woodland, although no obvious inter-area differences were found in the number of fledglings per successful pair. We suggest that a higher predation rate in the pseudo-steppe accounts for the higher proportion of failed nesting attempts. The body mass and breeding performance of owls was lower after a rainy winter and spring, but was not reduced in a dry year. Little Owls seem to be well adapted to the predominantly dry climate in these areas.