Dynamics in spatial use by Ospreys (Pandion haliaetus) during the breeding season revealed by GPS tracking

Abstract

The migratory behaviour of Ospreys (Pandion haliaetus) has been well studied using satellite telemetry, but studies on their behaviour in the breeding area are scarce. We caught and fitted 17 adult Ospreys with solar-powered GPS-enhanced satellite transmitters in northeast Germany and tracked them for up to 7 years. There was a high variation in home range size depending on sex, nesting site and breeding success. The home ranges of successfully breeding males (median 33.4 km2, 95% kernel density estimations) were significantly larger than those of females (median 4.6 km2) and varied in extent and shape between individuals. Some females made long excursions and sometimes spent the night at great distances to their nests after the juveniles had fledged but they also returned to the nesting area before they left for migration. The males’ home range areas were consistent during the breeding period. The proportion of water surfaces on the home range areas of males ranged between 9.6 and 29%. The overnight roosts were found in distances up to 7.83 km (median 980 m) for successfully breeding males and up to 105 km (median 568 m) for successfully breeding females. The correlation between overnight roost-nest distance and the corresponding home range area was significant for females but not for males. The overlap in the home ranges of individual males that occupied the same nests in different years varied between 37.3 and 54.7% of the mutual home ranges. Males partly included the same waterbodies in their home ranges, but they also visited different lakes. In the incubation and nestling phases, females are closely bound to the nest, whereas their mates can range over vast areas.