Habitat selection and breeding ecology of golden eagles in Sweden

Sammanfattning: The red-listed Golden Eagle (Aquila chrysaetos) population is estimated between 1200-1400 reproductive individuals in Sweden. This population is unusual as eagles predominantly nest in trees unlike most others that prefer cliffs. The central aim of this thesis was to study 1) reproductive performance in relation to food supply, 2) habitat composition of territories at different scales, 3) breeding home range size, and 4) habitat selection of Golden Eagles in Sweden. Data on annual breeding performance in 1980-2009 were obtained by regional Golden Eagle monitoring groups and data on indicators of food supplies by a long-term monitoring of small rodents, and for main prey species by hunting bag statistics for mountain hare and forest grouse. Adult Golden Eagles were trapped on their territories and fitted with GPS backpack transmitters in autumn 2010 and 2011, and position data from 2011 and 2012 breeding seasons were used for studying home range and habitat selection. Landcover maps and elevation data were used to characterize habitat properties in territories. Reproductive performance was highly variable among years, for example number of nestlings per breeding attempt ranged from 0.5-1.4 with a mean of >1, but this and other measures did not show 3-4 yr cycles as previously thought. However, both proportion of territories with nestlings and number of nestlings per occupied territory was positively related to primary prey (small game) indices in the same year. Habitat composition of territories was scale-dependent, with rugged terrain and old forest being overrepresented at the nest site scale, while clear-cuts on intermediate scales away from the nest. The GPS position data revealed some of the largest home ranges in Golden Eagle literature when derived from 50 and 95% kernel density estimators (KDE). In 2012, 50% KDEs ranged from approx. 5 − 110km², while 95% KDEs ranged from 70 − 580km². Home range size displayed a negative relationship to the proportion of clear-cuts within each home range. Analyses based on position data confirmed that the Eagles preferred coniferous forest, clear-cuts and steeper slopes. The here identified habitat and landscape preferences can be used for landscape management in the boreal region to support Golden Eagles.