During recent decades the Osprey population in Europe has grown and expanded, partly as a result of reintroduction. During 2013–17 a reintroduction programme was conducted in the Bay of Biscay. We describe the autumn movements of 12 GPS-tracked young Ospreys, and the survival of the translocated Ospreys. Using our and external data, we compare survival rates between satellite-tracked Ospreys and those simply ringed and discuss the potential negative effects of satellite devices. Satellite-tagged Ospreys used similar flyways and settled in the usual sub-Saharan wintering region of the Scottish birds but made no stopovers. Of the staging events 26.7% were recorded on electricity infrastructure, which represents a high risk, especially in the countries with a developed network. None of the 13 tracked birds survived to return, whereas the return rate of 41 non-tagged birds was 24.4%. Available information indicates a return rate of 6.2% (five from 80) for satellite-tagged juveniles from European migratory populations, which suggests that tagging is associated with a lower survival. Further investigation is needed to verify whether satellite tagging negatively affects the survival of juveniles. Meanwhile, we advise against satellite-tagging young Ospreys in reintroduction projects, and in other small populations, because it could reduce the chances of success and jeopardise their viability.
