Effective natal dispersal and age of maturity in the threatened Spanish Imperial Eagle Aquila adalberti: conservation implications: Capsule Dispersive capacity appears sufficient to establish natural re-occupation of the former range.

Author： González Luis Mariano Oria Javier Margalida Antoni Sánchez Roberto Prada Luis Caldera Javier Aranda Antonio Molina Jose Ignacio

Publisher： Taylor & Francis Ltd

ISSN： 0006-3657

Source： Bird Study, Vol.53, Iss.3, 2006-11, pp. : 285-293

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Abstract

Aims To document data on effective natal dispersal and age of maturity in the increasing, but fragmented, Spanish Imperial Eagle population.Methods Between 1990 and 2002, 84 nestlings from six of the 14 breeding nuclei of the species' range in Spain were tagged with metal and plastic leg-rings and radiotagged with VHF and satellite transmitters. Birds and breeding pairs were monitored annually throughout the distribution range for evidence of breeding status, movements, juvenile dispersal areas and behaviour prior to first-time pairing, establishment of a territory, and breeding.Results The mean effective natal dispersal distance was 101.2 km and the median was 80 km (range 3–310, n = 12). Depending on how philopatry was defined, between 42 and 50% of individuals were considered philopatric. The majority of the philopatric individuals bred for the first time on the border of the breeding distribution range. Birds tend to breed first in the last area they inhabited. During their first breeding attempt, most eagles lay eggs and most have subadult plumage at this time. Birds were first recorded as being paired and territorial at a mean age of 3.4 years (n = 9), first egg-laying occurred at 4.5 years (n = 10) and first successful breeding at five years (n = 6). The earliest known breeding age was two years in females and three years in males.Conclusion The dispersive capacity of Spanish Imperial Eagles appears sufficient to enable natural re-occupation of their former range. These results have important implications for the species conservation strategy, because the chance of contacting other breeding nuclei is greater than previously estimated and the natal dispersal distance has a relatively high colonizing capacity.