Nistplatzwahl und Bruterfolg der Blauracke (Coracias garrulus) im Südwesten der Iberischen Halbinsel

Nest-site selection and breeding success was studied in a breeding population of Roller (Coracias garrulus) in the Southwest of Spain. 567 nest-boxes were installed on electric pylons in seven different habitats: fallow land, cereals, helm oaks, olive groves, pasture land, irrigated crops (rice and maize) and shrubs. The more favoured habitats were the irrigated crops, the olive groves and the helm-oaks, while only the cereals were clearly avoided. Fallow land, pastures and shrublands were preferred approximately according to their availability in the area. The mean laying date of Rollers was significantly different between habitats, however, the other reproductive variables did not vary with habitat type. The seasonal trend in reproductive value of the Roller varied relative to habitat type. So, in olive groves and irrigated crops no clear seasonal trends were detected in clutch size, while a clear seasonal decline in clutch size was detected in the rest of the habitat types. The intensity of selection of each habitat was only marginally related to the hatching success of the rollers in Extremadura. These results indicate that the decrease in natural nest-sites as a result of the intensification of agriculture is the principal cause of the decline in Roller populations in contrast to previous studies which argued that this was a consequence of the decrease in available food.