Spatial use of non-breeding sites by adult GPS-tracked Ospreys <i>Pandion haliaetus</i> from Germany

Recent analyses of telemetry data on Ospreys Pandion haliaetus predominantly address migratory movements, whereas studies focusing on spatial use are rare, especially concerning the African non-breeding areas. We analysed GPS telemetry data of 15 adult Ospreys breeding in northeast Germany, assigned to 37 non-breeding events at non-breeding sites in Africa and south-western Europe. We calculated seasonal home ranges and investigated daily movements as well as overnight roosts. The females arrived in Africa about one month before the males. The home ranges of males correlated with those reported for their respective breeding seasons and were similar in size to those of the females. Half of the non-breeding sites were established on rivers, 36% on the coast and 14% on lakes, with no difference between sexes. Ospreys tracked for more than one year always returned to the same non-breeding sites. Daily home-range sizes varied during the non-breeding period, with the largest home ranges found in January, in parallel with the dry season. The average number of nights per overnight roost was lowest for river habitats and was related to the overall home-range size of the individuals. We highlight the importance of non-breeding sites for the survival of populations and suggest further studies to detect and mitigate threats to migratory bird species.