Severe feather deformation in greater white-fronted goose (Anser alb. albifrons) goslings during hot summer period on Kolguev Island 2016

In summer 2016, we observed premature feather malformation among goslings of greater white-fronted goose (Anser alb. albifrons), between 7 and 10 weeks of age on family gathering areas on Kolguev Island, Russia, the most important breeding island in the Western Palearctic. Rarely reported in wild birds, to our knowledge, this phenomenon has not been recorded in wild geese of this species, despite continuous ringing and marking of thousands of wild geese across Northern Europe and Arctic Siberia. This feather malformations were documented in 36 unfledged goslings showing weak feather basis, deformed or unevenly grown wing feathers or even dead feather buds. Approximately about one-third of all chicks were affected. Feather malformations like this, causing flightless chicks as a result, have never been noticed in any other of our 12 study years since 2006. The lesion was characterised by soft feather buds, weak or incomplete wing feathers and lack of feather development. No other abnormalities were observed in the goslings, so goslings did not differ in weight or body sizes. Affected fledglings never became airworthy and were killed in large numbers by predators or at latest perished during the Arctic winter. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10344-022-01603-9.