Nest-site selection and breeding success in the Roller (Coracias garrulus)in the Southwest of the Iberian peninsula

Nest-site selection and breeding success was studied in a breeding populati on 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 avoide d. Fallow land, pastures and shrublands were preferred approximately accord ing to their availability in the area. The mean laying date of Rollers was significantly different between habitats, however, the other reproductive v ariables did not vary with habitat type. The seasonal trend in reproductive value of the Roller varied relative to habitat type. So, in olive groves a nd irrigated crops no clear seasonal trends were detected in clutch size, w hile a clear seasonal decline in clutch size was detected in the rest of th e habitat types. The intensity of selection of each habitat was only margin ally related to the hatching success of the rollers in Extremadura. These r esults indicate that the decrease in natural nest-sites as a result of the intensification of agriculture is the principal cause of the decline in Rol ler populations in contrast to previous studies which argued that this was a consequence of the decrease in available food.