Dispersal of Golden Eagles Aquila chrysaetos during their first year of life

Abstract

Capsule: The area explored increased throughout the year and tended to be much larger for females than males. Aims: To explore how the process of juvenile dispersal unfolds spatially and temporally, and compare the size of the areas explored by the two sexes. Methods: Thirteen chicks were captured between June 2002 and July 2004, tagged with satellite transmitters, and subsequently tracked using the ARGOS system. Results: In both sexes the total area explored increased with time. The average (± sd) size of the area explored in the whole year was 3713 km2 (± 2586) in males and 10 652 km2 (±7451) in females. Both the monthly increase in the total area explored (individuals’ averages ranging from 22 to 2526 km2) and the overlap between areas used consecutively (about 25%) remained relatively constant throughout the year. Conversely, the size of the area used within a month, and the distance between consecutive areas, increased towards the end of the year; 87.5% of the individuals survived to their first year of life. Conclusions: While females are prominent dispersers and show a more eager exploratory behaviour, males remain within a more restricted area closer to the natal nest, and make more regular use of it. Differences in the total area explored might be linked to differences in food requirements, but other factors are also likely to be involved.