Skillnader i kungsörnens (Aquila chrysaetos) flyttningsmönster beroende på ålder och klimatfaktorer
En studie för skyddet av kungsörn
This study examines the factors that influence the seasonal movements of Golden Eagles (Aquila chrysaetos), and can thus provide important information that helps to improve the protection of the species. There were two main purposes of this study. First, I wanted to analyze the difference between preferences of juvenile and adult Golden Eagles in their choice of southern or northern hibernation areas. Do younger eagles prefer moving longer distance to southern areas of Sweden? Second, I wanted to investigate how the climate influenced the choice of date of migration in the fall. In other words, does an early winter arrival influence the migration date of Golden Eagles? I also investigated if food availability influenced the migration date in combination with winter arrival?For the statistical analyses, 14 years (1998-2011) of data on snow conditions, temperatures, food availability and records on banded eagles from the counties Ångermanland and Västerbotten were used.I found that young eagles preferred to move further south, while adults tended to move much shorter distances or remained in the nesting area during the winter. How early or late in the fall the eagles moved was mainly affected by the first day when the temperature was -10°C or below combined with the first day when the snow depth reached at least 8 cm. Another factor that seemed to affect the date of migration was the amount of food (smaller prey), which influenced the effects of temperature and snow cover. For example, there were instances when good food availability led to eagles deciding to stay longer despite early snowfall.This important knowledge on how climatic factors and food availability influence the migration of Golden eagles can be useful when developing conservation programs for their future protection.