Seasonal variation in the abundance and habitat use of Barn Owls Tyto alba on lowland farmland

We studied age structure, seasonal variation in abundance and habitat use in the Barn Owl Tyto alba on a lowland farmland area in central Portugal during 1991-93. Abundance varied markedly throughout the year and followed a similar pattern in different years. During the breeding season owls were scarce whereas in autumn their abundance was very high. Most of the owls occurring in the area were dispersing first-year individuals that probably only stayed for short periods. Lack of breeding sites might have been the cause of high turn-over, since Barn Owls usually breed when they are one year old. Owls preferred distinct habitat types in different periods of the year. Habitats with very tall and dense vegetation (sunflower, maize, reed beds) were not preferred and habitat structure seemed to have a great influence in habitat selection. Agricultural practices affected habitat utilization, and pastures, tilled fields and winter and summer culture stubbles were preferred on different times of the year. It is likely that Barn Owls need a certain degree of habitat heterogeneity to fulfill their foraging requirements throughout the year.