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Oryx (2009), 43:113-121 Cambridge University Press
Copyright © Fauna & Flora International 2009


A demographic description of the recovery of the Vulnerable Spanish imperial eagle Aquila adalberti

Enric Ortegaa1, Santi Mañosaa1, Antoni Margalidaa2 c1, Roberto Sáncheza3, Javier Oriaa4 and Luis Mariano Gonzáleza5

a1 Departament de Biologia Animal, Universitat de Barcelona, Barcelona, Spain.
a2 Bearded Vulture Study & Protection Group, Apdo. 43, E-25520 El Pont de Suert, Lleida, Spain.
a3 TRAGSA, c/Velázquez, Madrid, Spain.
a4 Boscaje S.L., Segovia, Spain.
a5 Dirección General para la Biodiversidad, Ministerio de Medio Ambiente, Madrid, Spain.
Article author query
ortega e [PubMed]  [Google Scholar]
mañosa s [PubMed]  [Google Scholar]
margalida a [PubMed]  [Google Scholar]
sánchez r [PubMed]  [Google Scholar]
oria j [PubMed]  [Google Scholar]
gonzález lm [PubMed]  [Google Scholar]


The population of the Vulnerable Spanish imperial eagle Aquila adalberti has experienced a gradual recovery from 38 pairs (1974) to 198 (2004). We analysed the spatial and temporal variation of the demographic parameters for 1981–2004. Annual productivity was 1.19–1.32 chicks per female and adult survival rate 0.918–0.986. Survival during the post-fledging period was 0.894 and the annual survival rate of the dispersing individuals was 0.561. Three phases of population evolution were distinguished: growth (1981–1993), stability or slight decrease (1994–1999) and growth (2000–2004). Variation in adult survival seems to explain this pattern for the first two periods. However, a large disparity between the observed growth rate and the modelled population growth in 2000–2004 is best explained if we assume that a decrease in the age of recruitment took place. This is supported by the recent increase in the frequency of non-adult birds in breeding pairs. The survival of unpaired eagles in dispersal areas is becoming more important for the maintenance of current population growth. Spatial variation of adult survival and breeding success is not congruent with the observed growth rate of the population, which suggests the existence of an important flow of individuals between populations. These results highlight the importance of addressing the conservation of the species from a global perspective and the need to focus on adult survival in breeding territories and on non-adult survival in dispersal areas.

(Received June 11 2007)

(Reviewed August 31 2007)

(Accepted February 11 2008)

KeywordsAquila adalberti; demography; population dynamics; Spain; Spanish imperial eagle


c1 Bearded Vulture Study & Protection Group, Apdo. 43, E-25520 El Pont de Suert, Lleida, Spain. E-mail margalida@inf.entorno.es