COOPERATIVELY BREEDING GROUPS OF CARRION CROW(CORVUS CORONE CORONE) IN NORTHERN SPAIN

Abstract

Abstract The Carrion Crow (Corvus corone) is almost invariably reported as a species breeding as unassisted pairs, but a population of Carrion Crows (Corvus c. corone) from northern Spain that we have been studying since 1995 regularly exhibits cooperative breeding. The Spanish population thus demonstrates that cooperative breeding can vary greatly across populations. Most of the breeding territories (73.3%) in Spain were held by cohesive groups, which consisted of up to nine birds (mode = 3 birds). The proportion of fledglings that delayed dispersal for one year varied between 12.2 and 47.5% for different cohorts. The corresponding values for juveniles postponing dispersal for two years were 4.9 and 19.2%. Philopatry was skewed toward males. Some social groups contained immigrants. Therefore, delayed juvenile dispersal was not the only route towards sociality. Up to three helpers provided food to the nestling and at least one helper was found in all the groups surveyed. However, some group members refrai...