Population changes and breeding ecology of the Cirl Bunting Emberiza cirlus in eastern Spain

Abstract

The number of Cirl Bunting Emberiza cirlus breeding pairs was recorded from 1976 to 1993 in orange plantations in eastern Spain, and some aspects of the breeding ecology of this species were studied from 1989 to 1993. Breeding densities varied from 0.6 to 10.1 pairs per 10 ha, being highest during the last 5 years. Breeding density each year was positively correlated with rainfall during the previous December–March period, but not to winter temperatures. The mean laying date was 17 April, and between-year variation was almost entirely determined (97% of the variation) by rainfall during December–March. The last clutches were laid by early July. Mean clutch size was 3.5 eggs. Clutch size increased during the first part of the season and then declined. About half of the nests were successful and half of the eggs laid produced fledglings. Predation accounted for most (35%) of the individual losses and was heavier early in the season. A logistic model was fitted to the weight data of the nestlings. Growth rate was 0.58 g day-1 g-1 and asymptotic weight was 15.6 g, which is about 65% of the adult weight. We suggest that the increase of the breeding population during the last years is related to the increase in winter rainfall, probably increasing food supply. © 1998 British Trust for Ornithology.