NATAL DISPERSAL IN RELATION TO NUTRITIONAL CONDITION IN SPANISH IMPERIAL EAGLES

I analyzed the factors determining the length of the predispersal period in the Spanish Imperial Eagle Aquila adalberti, using the information supplied by 21 radio-tagged young in Donana National Park (SW Spain) in 1986-1988. The average length of the predispersal period was 9.2 d. Urea and uric acid levels in blood, a measure of body condition, were significantly related to the length of this period. The results suggest that factors other than competition with adults, make young disperse as soon as possible. Similarities in the dispersal tendency between siblings from the same brood seem to be an effect of covariance with other factors linked to the nest than a genetically determined behaviour.