Parental behaviour of Spanish Imperial Eagles Aquila adalberti: sexual differences in a moderately dimorphic raptor

[Capsule]: The sexes make significantly different contributions in the tasks of nest-building, incubation and food provisioning to chicks.[Aims]: To determine the division of parental activities during breeding (nest-building, incubation, brooding, food provisioning and feeding).[Methods]: Between 1991 and 1998 focal observations were made at nests using 20–60× telescopes. During the incubation period, 11 pairs were studied involving a total of 2812 observation hours over 269 days. During the chick-rearing period, seven pairs were studied involving a total of 5499 observation hours spread over 503 days. The birds were sexed and identified individually on the basis of size, position during copulation, vocalization and plumage differences.[Results]: Significant differences were found between the sexes in parental behaviour. Males scarcely participated in incubation and contributed significantly more than the females only in food provisioning, both during incubation (food transfers to feed the female) and during chick-rearing (to feed the chicks). Females were responsible for most of the incubation, nest-building (during incubation and chick-rearing), brooding, shading and feeding of chicks. Nest attendance by females decreased over time. In both sexes, food provisioning increased with brood size.[Conclusion]: Intersexual differences are discussed in the context of the reversed sexual size dimorphism and parental investment strategies. We suggest that in Spanish Imperial Eagles reversed sexual size dimorphism is best explained by the prey capture difficulty hypothesis, than by parental role division during reproduction.This study was jointly funded by the Dirección General para la Biodiversidad del Ministerio de Medio Ambiente and Consejería de Medio Ambiente of the Comunidad de Madrid. Valuable information was provided by the autonomous communities of Madrid, Castilla y León, Castilla-La Mancha and Extremadura.Peer reviewe