Breeding biology of the RollerCoracias garrulusin farming areas of the southwest Iberian Peninsula

We studied the breeding biology of Rollers nesting in nestboxes installed in farming areas of Extremadura (southwest Spain). Laying dates of Rollers in Extremadura are the earliest in the Palearctic region. Clutch size was larger than in northern populations. In the studied population, yearly variation in clutch size could be explained by yearly variation in the timing of reproduction. Reproductive rates were higher than in more northerly populations. A seasonal decrease in breeding success of Rollers in Extremadura was caused by a reduction in clutch size and the percentage of hatched eggs, and a seasonal increase in mortality rate. The most successful clutches were those with six eggs although clutches with four and five eggs were the most frequent in Extremadura.