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

Abstract

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.

Keywords

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

Notes

Acknowledgments

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.

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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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