Abstract: Ship-assisted vagrancy of Snowy Owls into Western Europe has been the subject of debate for a long time. In November 2021, three Snowy Owls were sighted in Northern Spain. Two of these owls were found dead. Following post-mortem exam, feather stable isotope analysis was performed to confirm/discard the potential wild origin of these birds. Body and flight feathers were analysed for the deuterium proportion, an indicator of the latitude where feathers were grown. The two studied birds had very negative delta values for deuterium (2Hf): -108.21 (N = 3, sd = 0.44) and -132.22 (N = 3, sd = 0.56) for the female and the male, respectively. Furthermore one bird presented severe emaciation and the other developed aspergillosis upon arrival. These results point towards ship-assisted vagrancy of the Snowy Owls, and rule out the possibility of them being raised and thus being escapees from captivity in Western Europe.
