Journal of Ornithology

, Volume 148, Issue 3, pp 309–322 | Cite as

A long-term large-scale study of the breeding biology of the Spanish imperial eagle (Aquila adalberti)

  • Antoni Margalida
  • Luis Mariano González
  • Roberto Sánchez
  • Javier Oria
  • Luis Prada
  • Javier Caldera
  • Antonio Aranda
  • José Ignacio Molina
Original Article


We present data from a 17-year study of the population biology of a growing population of Spanish imperial eagles Aquila adalberti across most of its breeding range. The objective of this study was to analyse the effects of age, supplemental feeding and rabbit haemorrhagic disease (RHD) on several breeding parameters of this population of eagles. Average clutch size was 2.2 eggs per clutch, and the average incubation time was 41.7 days per clutch. Fledging occurred an average of 76.8 days after hatching, the length of the fledgling period was not correlated to clutch size. The annual average percentage of pairs laying eggs was 88%. A significant reduction in the percentage of pairs laying eggs in the period 1992–1994 (from 91 to 81%) coincided with most of the eagles’ territories being affected by the rabbit epizootic disease, RHD, which reduced their food supply significantly. Average productivity was 1.23 chicks per monitored territory, average breeding success was 1.40 chicks in a clutch per territory and the average fledging rate was 1.69 chicks per territory with hatching success. The main known causes of breeding failure during incubation were nest collapse and human disturbance. During chick-rearing, total or partial chick losses were mainly caused by siblicide, disease, malnutrition or nest collapse. In 26.2% of the 1372 monitored breeding attempts, at least one of the breeding birds was a subadult (the male in 56.1% of the cases, the female in 15.5% and both sexes in 28.4% of cases). In cases of mixed-aged pairs (n = 205), 70.7% were the result of a substitution, and 29.3% were the result of the forming of a new pair. Egg laying took place significantly earlier and breeding success was higher in territories occupied by adults than in those occupied by subadults. Breeding parameters were higher in high-quality (rabbit-rich) territories than in low-quality (rabbit-poor) territories, but only for those territories occupied by adults. The values obtained in the territories occupied by adults were only significantly higher than in those of the subadults in high-quality territories. Age and territory quality thus simultaneously affected reproductive output.


Breeding biology Breeding experience Breeding parameters Habitat quality Spanish imperial eagle Supplemental feeding 



Thanks to J. Caballero, J. Sánchez, I. López, L. Bolonio, M. Fernández, M. Panadero, J. Panadero, C. Soria, A. Mojena, L. López, J. Guzmán, D. Martín, A. Calvo and C. Dávila for their help with the fieldwork. We would particularly like to thank V.G. Matarranz, who, with his usual skill and know-how, tagged all the nestlings. Thanks also to J.P. Castaño, J.M. Blanco, F. Sánchez, N. González, F. de la Orden, F. Jiménez, J.I. Mosqueda, A. Sánchez, M.J. Palacios, S. Centenera, B. Heredia, C. Rodríguez Vigal, C. Urdiales, T. Gullick, P. Maldonado and the official wardens of the Autonomous regions and the National Park of Doñana for the information on sightings they kindly provided. We are also greatful to all the landowners that hold the Spanish imperial eagles. The comments of G.R. Bortolotti and B.E. Arroyo improved the manuscript and S. Hardie translated the text into English. This study was jointly funded by the framework of the National Strategy and Recovery Plans for the species by the Dirección General para la Biodiversidad del Ministerio de Medio Ambiente and the Consejerías de Medio Ambiente of the Autonomous Communities of Madrid, Castilla y León, Castilla-La Mancha and Extremadura; and by the European Commission throughout LIFE-projects 99/NAT/E/006336 and 03/NAT/E/000050.


  1. Aparicio JM (1994) The seasonal decline in clutch size: an experiment with supplementary food in the kestrel, Falco tinnunculus. Oikos 71:451–458CrossRefGoogle Scholar
  2. Aparicio JM, Bonal R (2002) Effects of food supplementation and habitat selection of timing of lesser kestrel breeding. Ecology 83:873–877CrossRefGoogle Scholar
  3. Argüello JL, Llanos A, Pérez-Ordoyo LI (1988) Enfermedad vírica hemorrágica del conejo en España. Med Vet 5:645–650Google Scholar
  4. Balbontín J, Penteriani V, Ferrer M (2003) Variation in the age of mates as an early warning signal of changes in population trends? The case of Bonelli’s eagle in Andalusia. Biol Conserv 109:417–423CrossRefGoogle Scholar
  5. Bavoux C, Burneleau G, Picard M (1998) La nidification du busard des roseaux Circus a. aeruginosus en Charente-Maritime (France). Analyse des données en fonction de l’âge des nicheurs. Alauda 66:299–305Google Scholar
  6. Beecham JJ, Kochert MN (1975). Breeding biology of the Golden Eagle in southwestern Idaho. Wilson Bull 87:506–513Google Scholar
  7. BirdLife International (2004) Threatened birds of the world 2004. CD-ROM. BirdLife International, CambridgeGoogle Scholar
  8. Blanco JC, Villafuerte R (1993) Factores ecológicos que influyen sobre las poblaciones de conejos. Incidencia de la Enfermedad Hemorrágica. TRAGSA-Ministerio de Medio Ambiente, MadridGoogle Scholar
  9. Broomer JE, Pietiäinen H, Kolunen H (1998) The effect of age at first breeding on Ural owl lifetime reproductive success and fitness under cyclic food conditions. J Anim Ecol 67:359–369CrossRefGoogle Scholar
  10. Brown LH (1969) Status and breeding success of Golden Eagles in north-west Sutherland in 1967. Brit Birds 62:345–363Google Scholar
  11. Brown L, Amadon D (1968) Eagles, hawks and falcons of the world. Country Life, LondonGoogle Scholar
  12. Brown LH, Gargett V, Steyn P (1977) Breeding success in some African eagles related to theories about sibling aggression and its effects. Ostrich 48:65–71Google Scholar
  13. Calderón J, Castroviejo J, García L, Ferrer M (1987) El Águila Imperial (Aquila adalberti) en Doñana: algunos aspectos de su reproducción. Alytes 5:47–72Google Scholar
  14. Cheylan G (1981) Description des principaux paramètres de la reproduction. Rapaces Méditerranéens 1:3–5Google Scholar
  15. Cooke BD (2002) Rabbit haemorrhagic disease: field epidemiology and the management of wild rabbits populations. Rev Sci Tech Off Int Epiz 21:347–358Google Scholar
  16. Cramp S, Simmons KEL (1980) Handbook of the birds of Europe, the Middle East, and North Africa, vol 2. Oxford University Press, OxfordGoogle Scholar
  17. Danko S, Chavko J (1996) Breeding of the imperial eagle Aquila heliaca in Slovakia. In: Meyburg B-U, Chancellor RD (eds) Eagle studies. WWBP, Berlin, pp 415–423Google Scholar
  18. del Hoyo J, Eliott A, Sargatal J (1994) Handbook of the birds of the world, vol 2. Lynx, BarcelonaGoogle Scholar
  19. Feare CJ (1976) Desertion and abnormal development in a colony of Sooty Terns (Sterna fuscata) infested by virus ticks. Ibis 118:112–115Google Scholar
  20. Fergusson-Lees J, Christie DA (2001) Raptors of the world. Christopher Helm Publ, LondonGoogle Scholar
  21. Ferrer M (1994) Nutritional condition of Spanish imperial eagle nestlings Aquila adalberti. Bird Study 41:120–123CrossRefGoogle Scholar
  22. Ferrer M (2001) The Spanish imperial eagle. Lynx, BarcelonaGoogle Scholar
  23. Ferrer M, Bisson I (2003) Age and territory-quality effects on fecundity in the Spanish imperial eagle (Aquila adalberti). Auk 120:180–186CrossRefGoogle Scholar
  24. Ferrer M, Penteriani V, Balbontín J, Pandolfi M (2003) The proportion of immature breeders as a reliable early warning signal of population decline: evidence from the Spanish imperial eagle in Doñana. Biol Conserv 114:463–466CrossRefGoogle Scholar
  25. Forslund P, Pärt T (1995) Age and reproduction in birds: hypotheses and tests. Trends Ecol Evol 10:374–378CrossRefGoogle Scholar
  26. Forsman D (1999) The raptors of Europe and the Middle east. A handbook of field identification. T and AD Poyser, LondonGoogle Scholar
  27. Gargett V (1977) A 13-year population study of the black eagle in the Matopos, Rhodesia 1964–1977. Ostrich 48:17–27Google Scholar
  28. Garzón J (1973) Contribución al estudio del status, alimentación y protección de las Falconiformes en España Central. Ardeola 19:279–330Google Scholar
  29. Gil-Sánchez JM, Moleón M, Otero M, Bautista J (2004) A nine-year study of successful breeding in a Bonelli’s eagle population in southeast Spain: a basis for conservation. Biol Conserv 118:685–694CrossRefGoogle Scholar
  30. González LM (1991) Historial natural del Águila Imperial Ibérica (Aquila adalberti Brehm, 1861). Colección Técnica. Instituto para la Conservación de la Naturaleza, MadridGoogle Scholar
  31. González LM (1996) Tendencias poblacionales y estatus de conservación del Águila imperial ibérica (Aquila adalberti) en España durante los últimos veinte años. In: Muntaner J, Mayol J (eds) Biología y Conservación de las Rapaces Mediterráneas. Monografia 4. SEO, Madrid, pp 61–65Google Scholar
  32. González LM, Oria J (2003) Águila imperial Ibérica, Aquila adalberti. In: Martí R, del Moral JC (eds) Atlas de las aves reproductoras de España. Dirección General de Conservación de la Naturaleza – Sociedad Española de Ornitología, Madrid, pp 186–187Google Scholar
  33. González LM, Oria J (2004) Águila imperial Ibérica, Aquila adalberti. In: Madroño A, González C, Atienza JC (eds) Libro Rojo de las Aves de España. Dirección General para la Biodiversidad (MMA)-Sociedad Española de Ornitología, Madrid, pp 145–152Google Scholar
  34. González LM, Bustamante J, Hiraldo F (1990) Factors influencing the present distribution of the Spanish imperial eagle (Aquila adalberti). Biol Conserv 51:311–319CrossRefGoogle Scholar
  35. González LM, Arroyo BE, Margalida A, Sánchez R, Oria J (2006a) Effect of human activities on the behaviour of breeding Spanish imperial eagles Aquila adalberti: management implications for the conservation of a threatened species. Anim Conserv 9:85–93CrossRefGoogle Scholar
  36. González LM, Margalida A, Oria J, Sánchez R (2006b) Supplemental feeding as management tool to improve breeding success in the Spanish imperial eagle (Aquila adalberti). Biol Conserv 129:477–486CrossRefGoogle Scholar
  37. González LM, Oria J, Margalida A, Sánchez R, Prada L, Caldera J, Aranda A, Molina JI (2006c) Effective natal dispersal and age of maturity in the threatened Spanish imperial eagle Aquila adalberti: conservation implications. Bird Study 53:285–293Google Scholar
  38. González LM, Margalida A, Mañosa S, Sánchez R, Oria J, Molina JI, Caldera J, Aranda A, Prada L (2007) Causes and spatiotemporal variations of non-natural mortality in endangered Spanish Imperial Eagle (Aquila adalberti) during a recovery period. OryxGoogle Scholar
  39. Green RE (2004) Breeding biology. In: Sutherland WJ, Newton I, Green RE (eds) Bird ecology and conservation: a handbook of techniques. Oxford University Press, Oxford, pp 57–83Google Scholar
  40. Grier JW (1980) Modeling approaches to bald eagle population dynamics. Wildl Soc Bull 8:316–322.Google Scholar
  41. Hansen AJ (1987) Regulation of bald eagle reproductive rates in Southeast Alaska. Ecology 68:1387–1392CrossRefGoogle Scholar
  42. Hansen AJ, Hodges JI (1985) High rates of nonbreeding adult bald eagles in southeastern Alaska. J. Wildl Manage 49:454–458Google Scholar
  43. Herman CM (1955) Diseases of birds. In: Wolfson A (ed) Recent studies in avian biology. Urbana, University of Illinois Press, pp 450–467Google Scholar
  44. Hiraldo F, Delibes M, Calderón J (1976) Sobre el status taxonómico del Águila Imperial ibérica. Doñana Acta Vert 3:171–182Google Scholar
  45. Hiraldo F, Negro JJ, Donázar JA, Gaona P (1996) A demographic model for a population of the endangered lesser kestrel in southern Spain. J Appl Ecol 33:1085–1093CrossRefGoogle Scholar
  46. Kadmon R (1993) Population dynamic consequences of habitat heterogeneity: an experimental study. Ecology 74:816–825CrossRefGoogle Scholar
  47. Katzner TE, Bragin EA, Knick ST, Smith AT (2005) Relationship between demographics and diet specificity of imperial eagles Aquila heliaca in Kazakhstan. Ibis 147:576–586CrossRefGoogle Scholar
  48. Korpimäki E, Wiehn J (1998) Clutch size of kestrels: seasonal decline and experimental evidence for food limitation under fluctuating food conditions. Oikos 83:259–272CrossRefGoogle Scholar
  49. Kostrzewa R, Kostrzewa A (1991) Winter weather, spring and summer density, and subsequent breeding success of Eurasian Kestrels, Common Buzzards, and Northern Goshawks. Auk 108:342–347Google Scholar
  50. Lack DL (1954). The natural regulation of animal numbers. Oxford University Press, ClarendonGoogle Scholar
  51. Lequette B, Weimerskirch H (1992) Influence of parental experience on the growth of Wandering Albatross chicks. Condor 92:726–731CrossRefGoogle Scholar
  52. Margalida A, Bertran J (2000) Nest-building behaviour of the Bearded Vulture (Gypaetus barbatus). Ardea 88:259–264Google Scholar
  53. Margalida A, García D, Bertran J, Heredia R (2003) Breeding biology and success of the Bearded Vulture (Gypaetus barbatus) in the eastern Pyrenees. Ibis 145:244–252CrossRefGoogle Scholar
  54. Meyburg B-U (1975) On the biology of the Spanish imperial eagle (Aquila heliaca adalberti). Ardeola 21:245–283Google Scholar
  55. Meyburg B-U (1987) Clutch size, nestling aggression and breeding success of the Spanish imperial Eagle. Brit Birds 80:308–320Google Scholar
  56. Meyburg BU, Garzón J (1973) Sobre la protección del Aguila Imperial Ibérica Aquila heliaca adalberti aminorando artificialmente la mortalidad juvenil. Ardeola 19:107–128Google Scholar
  57. Morrison JL (1999) Breeding biology and productivity of Florida’s Crested Caracaras. Condor 101:505–517CrossRefGoogle Scholar
  58. Newton I (1979) Population ecology of raptors. T and AD Poyser, LondonGoogle Scholar
  59. Newton I (1989) Sparrowhawk. In: Newton I (ed) Lifetime reproduction in birds. Academic Press, London, pp 201–219Google Scholar
  60. Newton I, Marquiss M (1981) Effects of additional food on laying date and clutch size in sparrowhawks. Orn Scand 12:225–229Google Scholar
  61. Newton I, Marquiss M (1984) Seasonal trend in the breeding performance of Sparrowhawks. J Anim Ecol 53:809–829CrossRefGoogle Scholar
  62. Nichols JD, Hensler GL, Sykes P (1980) Demography of the Everglade kite: implications for population management. Ecol Model 9:215–232CrossRefGoogle Scholar
  63. Nielsen T, Drachmann J (2003) Age-dependent reproductive performance in Northern Goshawks Accipiter gentilis. Ibis 145:1–8CrossRefGoogle Scholar
  64. Pedrini P, Sergio F (2001) Density, productivity, diet, and human persecution of golden eagles (Aquila chrysäetos) in the central-eastern Italian Alps. J Raptor Res 35:40–48Google Scholar
  65. Penteriani V, Gallardo M, Roche P (2002) Landscape structure and food supply affect eagle owl Bubo bubo density and breeding performance: a case of intra-population heterogeneity. J Zool Lond 257:365–372CrossRefGoogle Scholar
  66. Penteriani V, Balbontín J, Ferrer M (2003) Simultaneous effects of age and territory quality on fecundity in Bonelli’s eagle Hieraaetus fasciatus. Ibis 145:E77–E82Google Scholar
  67. Perrins CM (1970) The timing of birds’ breeding seasons. Ibis 112:242–255Google Scholar
  68. Perrins CM, Birkhead TR (1983) Avian ecology. Blackie and Sons, LondonGoogle Scholar
  69. Pianka ER (1983) Evolutionary ecology. Harper and Row, New YorkGoogle Scholar
  70. Piorno V, Villafuerte R (2003) Evolución reciente de las poblaciones de conejo de monte en España: el impacto de la enfermedad hemorrágico vírica (EHV). In: VI Jornadas de la SECEM. SECEM, Ciudad Real, p 39Google Scholar
  71. Postupalsky S (1974) Raptor reproductive success: some problems with methods, criteria and terminology. In: Hamerstron FN, Harrel BE, Olendorff RR (eds) Management of raptors. Raptor Research Found, Vermillion, pp 21–31Google Scholar
  72. Real J, Mañosa S (1997) Demography and conservation of western European Bonelli’s eagle Hieraaetus fasciatus populations. Biol Conserv 79:59–66CrossRefGoogle Scholar
  73. Sánchez-Zapata JA, Calvo JF, Carrete M, Martínez JE (2000) Age and breeding success of a golden eagle Aquila chrysaetos population in southeastern Spain. Bird Study 47:235–237CrossRefGoogle Scholar
  74. Sokal RR, Rohlf FJ (1995) Biometry, 2nd edn. WH Freeman, San FranciscoGoogle Scholar
  75. Steenhof K (1987) Assessing raptor reproductive success and productivity. In: Giron Pendleton BA, Millsap BA, Cline KW, Bird DM (eds) Raptor management techniques manual. National Wildlife Federation, Washington D.C., pp 157–170Google Scholar
  76. Steenhof K, Kochert MN, Doremus JH (1983) Nesting of subadult golden eagles in southwestern Idaho. Auk 100:743–747Google Scholar
  77. Steenhof K, Kochert MN, McDonald TL (1997) Interactive effects of prey and weather on golden eagle reproduction. J Anim Ecol 66:350–362CrossRefGoogle Scholar
  78. Svehlik J, Meyburg B-U (1979) Gelegegröße und Bruterfolg des Schreiadlers (Aquila pomarina) und des Kaiseradlers (Aquila heliaca) in den ostslowakischen Karpaten 1960–1978. J Ornithol 120:406–415CrossRefGoogle Scholar
  79. Valverde JA (1960) Vertebrados de las Marismas del Guadalquivir. Arch Inst Aclim Almería 9:1–168Google Scholar
  80. Villafuerte R, Calvete C, Gortázar C, Moreno S (1994) First epizootic of rabbit haemorrhagic disease (RHD) in free living populations of Oryctolagus cuniculus at Doñana National Park, SW Spain. J Wildl Dis 30:176–179PubMedGoogle Scholar
  81. Villafuerte R, Calvete C, Blanco JC, Lucientes J (1995) Incidence of viral haemorrhagic disease in wild rabbit populations in Spain. Mammalia 59:651–659CrossRefGoogle Scholar
  82. Viñuela J (2000) Opposing selective pressures on hatching asynchrony: egg viability, brood reduction, and nestling growth. Behav Ecol Sociobiol 48:333–343CrossRefGoogle Scholar
  83. Watson J (1997) The golden eagle. T and AD Poyser, LondonGoogle Scholar
  84. Wiehn J, Korpimäki E (1997) Food limitation on brood size: experimental evidence in the Eurasian kestrel. Ecology 78:2043–2050Google Scholar
  85. Williams GC (1966) Natural selection, the costs of reproduction and a refinement of Lack’s principle. Am Nat 100:687–690CrossRefGoogle Scholar
  86. Wimberger PH (1984) The use of green plant material in bird nests to avoid ectoparasites. Auk 101:651–658Google Scholar
  87. Wyllie I, Newton I (1991) Demography of an increasing population of sparrowhawks. J Anim Ecol 60:749–766CrossRefGoogle Scholar

Copyright information

© Dt. Ornithologen-Gesellschaft e.V. 2007

Authors and Affiliations

  • Antoni Margalida
    • 1
  • Luis Mariano González
    • 2
  • Roberto Sánchez
    • 3
  • Javier Oria
    • 4
  • Luis Prada
    • 5
  • Javier Caldera
    • 6
  • Antonio Aranda
    • 7
  • José Ignacio Molina
    • 8
  1. 1.Bearded Vulture Study and Protection GroupLleidaSpain
  2. 2.Dirección General para la BiodiversidadMinisterio de Medio AmbienteMadridSpain
  3. 3.Fundación CBD-HabitatMadridSpain
  4. 4.Boscaje S.LSegoviaSpain
  5. 5.Dirección General del Medio NaturalConsejería de Medio AmbienteMadridSpain
  6. 6.Dirección General de Medio AmbienteJunta de ExtremaduraSierra de Fuentes CáceresSpain
  7. 7.Dirección General del Medio NaturalJunta de Comunidades de Castilla-La ManchaToledoSpain
  8. 8.Dirección General del Medio NaturalConsejería de Medio AmbienteValladolidSpain

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