Moving away from home: Early life movements and space use in juvenile Montagu’s Harriers (Circus pygargus) from central Italy

Assessing individual differences and variability in animal movement patterns is essential to improve our understanding of the evolution and ontogeny of migratory strategies. In long-distance migratory species, fledged juveniles often rely on an extremely restricted time span to learn the essential skills for survival and to prepare for migration, possibly the most risky phase of their lives. Collecting detailed information on the dynamics of the movements during the crucial pre-migratory phase is hence essential to understand the solutions developed by migratory species in different environmental contexts. Here, we used high-resolution GPS/GSM transmitters to collect information on the movement ecology of seven juvenile Montagu's Harriers (Circus pygargus) born in central Italy, investigating their early life stages, namely the post-fledging dependence period (PFDP) and the pre-migratory phase (PMP), until autumn migration. After fledging, individuals showed high variability (both in space and time) in home range size, daily distances covered (6.88 ± 11.44 km/day), distance from the nest (1.45 ± 2.8 km) and PFDP length (23.3 ± 5.3 days). Residence time at the natal site significantly decreased, while time interval between revists in the natal area significantly increased, as the PFDP progressed. During the PMP, explored areas and distance from the nest (max value up to 320.8 km) varied among individuals, despite daily distances covered (27 ± 40 km/day) and time allocation between traveling (60.7%) and foraging (39.3%) were similar across individuals. The PMP lasted 38 ± 14 days. Land cover composition of foraging locations was mostly represented by agricultural lands (∼78.2%), though habitat use differed among individuals. More than 76% of such locations were outside protected areas. This individual-based tracking study represents a novel approach that improves previous knowledge based on field studies on the early life stages of the Montagu's Harrier. High inter-individual variability in movement patterns, broad-range exploratory movements and foraging locations outside the protected area network make the application of standard conservation measures difficult, raising concerns about the long-term preservation of this vulnerable migratory species in Italy.