Movements of Juvenile Hen Harriers (Circus cyaneus) Tracked by Satellite Telemetry in Spain

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The Hen Harrier (Circus cyaneus) is a medium-sized raptor with a broad distribution across the Palearctic. In Spain, Hen Harrier behaviour is diverse due to being at the southern limit of its distribution, and the margins of distributions tend to show greater variability in the strategies and behaviours of animals. This study focused on juvenile dispersal, using GPS/GSM data from seven individuals to define movement patterns, compare variables between sexes, and analyse differences between the first and second years of dispersal. To analyse the movements during each annual period, six variables were considered, namely the mean distance from nest location, maximum distance from nest location, mean daily distance travelled, total distance travelled, 95% weekly kernel, and 95% total kernel. In their first year after leaving the nest, the Hen Harriers began dispersal movements on 21 August ± 34.41 days, with highly variable distances and durations among individuals. They travelled an average total of 6774.66 ± 5360.46 km over the two first years, with some significant differences between sexes and periods in terms of movement patterns, particularly in the daily and total distances travelled. Overall, the maximum distance from nest location and the total distance travelled were greater in the first year of dispersal than in the second year, indicating, as expected, an improved understanding of their environment and more efficient movements. The juvenile dispersal behaviour of the Hen Harrier is highly variable and represents the most vulnerable season for survival as the birds navigate new and unexplored territories.