Ferrer M., Garcia L. & Cadenas R. (1990) Long-term changes in nest defense intensity of the Spanish Imperial Eagle Aquila adalberti. ARDEA 78 (3): 395-398

This paper deals with the variations recorded in the nest defence of the Imperial Eagle Aquila adalberti after the declaration of Donana as a national park (Parque Nacional Donana, SW Spain) and the cessation of strong human pressure. Increases have been detected in the defence and number of attacks during the reproductive cycle as well as over the years. The latter is interpreted as behaviour learned by adult eagles having long reproductive lives whose defensive conduct has been positively reinforced by numerous nest visits made by investigators.