Spanish imperial eagle (Aquila adalberti)

Also known as: Adalbert’s eagle, White-shouldered eagle
Synonyms: Aquila heliaca adalberti
Spanish: Aguila Imperial Ibérica
GenusAquila (1)
SizeLength: 75 – 84 cm (2)

The Spanish imperial eagle is classified as Vulnerable (VU) on the IUCN Red List 2006 (1) and is listed on Appendices I and II of both CITES (3) and the Convention on Migratory Species (CMS or Bonn Convention) (4). It is also listed on Appendices II and III of the Berne Convention of European Wildlife and Natural Habitats (5) and Annex I of the EC Birds Directive (6).

This large eagle has a pale cream head and neck, but dark brown feathers elsewhere. There is a distinctive white area on the shoulders and a pale grey area on the upper tail, and the species can be recognised by its particularly flat gliding flight. It gives a repeated barking ‘owk’ when calling. Juveniles are red-brown fading to pale brown with dark flight feathers and white fringes (2).

The Spanish imperial eagle breeds in central and southwest Spain, with populations found in the Sierras of Guadarrama and Gredos, the plains of the Tajo and Tiétar rivers, Monters de Toledo, the central hills of Extremadura, the Alcudia valley, Sorena Morena and the Guadalquivir marshes. It previously bred in Portugal, Algeria and Morocco, but is now only found there as a vagrant (2). It is also found in France and Gibraltar as a vagrant (1).

Inhabits cork oak forests, plains and hills in central Spain, flood plains and dunes in the Guadalquivir marshes and on high mountain slopes in the Sistema Central, where irrigated farmland is absent (2).

Adult Spanish imperial eagles occupy territories in pairs all year-round (7). They defend these territories from intrusion by other raptors, allowing only immature members of their own species to enter (8). Nests are built in tall oak trees, in small stands of trees far from human disturbance (7). During the breeding season, both the male and female of the monogamous pair will participate in the incubation of the eggs and the care of the chicks. Prey is torn into manageable pieces for the chicks until they are ready to hunt for themselves. Parent eagles will even shelter the chicks from heavy rain (8).

Feeding almost exclusively on rabbits, the Spanish imperial eagle’s population density, range and reproductive performance are influenced by the abundance and distribution of prey in the area (2). This eagle species is also known to eat greylag geese in southern Spain in the winter (9).

In the 1960s, with just 30 pairs remaining, conservation efforts succeeded in increasing the population of the Spanish imperial eagle by a considerable amount. However, since 1994, the population has been allowed to decline again to just 160 pairs. There are several causes of this decline: habitat fragmentation due to deforestation for agricultural land and timber has disturbed breeding grounds, intentional poisoning on hunting reserves to reduce natural predators of game species, lead shot poisoning as a result of ingestion of game killed with bullets, and electrocution on power cables (2). Approximately 80% of eagles killed on power lines are female, causing a greater impact on this monogamous species than if equal numbers of males and females were killed (10).

The Spanish imperial eagle relies mainly on rabbits as prey, and following drops in rabbit abundance due to shooting and disease, food supplies have been limited causing reduced breeding success (2) (11).

The Spanish imperial eagle is legally protected in Spain, and 62% of the breeding population occurs in 20 protected areas. A European action plan was published in 1996, and national and regional governments have worked to implement a coordinated conservation plan. A reintroduction plan has seen 13 young released successfully (2).

The action plan proposes the discouragement of intentional poisoning, as well as annual surveying of the breeding population, protection and management of all breeding sites, increasing the rabbit population and modifying dangerous power lines (2). The modification of just 19% of power poles in the range of the eagle could reduce total mortality by 52% (12).

For further information on the Spanish imperial species see:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. IUCN Red List (May, 2006)
  2. BirdLife International (February, 2005)
  3. CITES (February, 2005)
  4. CMS (February, 2005)
  5. Berne Convention (February, 2005)
  6. EC Birds Directive (February, 2005)
  7. Bisson, I.A., Ferrer, M. and Bird, D.M. (2002) Factors influencing nest-site selection by Spanish imperial eagles. Journal of Field Ornithology, 73(3): 298 - 302.
  8. Meyburg, B.U. (1975) On the biology of the Spanish imperial eagle. Publicado En Ardeda, 21: 1 - 10.
  9. Pain, D.J., Meharg, A.A., Ferrer, M., Taggart, M. and Penteriani, V. (2005) Lead concentrations in bones and feathers of the globally threatened Spanish imperial eagle. Biological Conservation, 121(4): 603 - 610.
  10. Ferrer, M. and Hiraldo, F. (1992) Man-induced sex-biased mortality in the Spanish imperial eagle. Biological Conservation, 60(1): 57 - 60.
  11. Ferrer, M. and Negro, J.J. (2004) The near extinction of two large European predators: Super specialists pay a price. Conservation Biology, 118(2): 183 - 193.
  12. Janss, G.F.E. and Ferrer, M. (2001) Avian electrocution mortality in relation to pole design and adjacent habitat in Spain. Bird Conservation International, 11(1): 3 - 12.