Sea crossings of migratory pink?footed geese: seasonal effects of winds on flying and stopping behaviour

Migratory birds may need to cross barriers such as seas, without opportunities rest or refuel. Waterbirds, unlike land birds, can stop at sea wait for better winds and thus be less selective supportive departure tolerate larger drift. However, pay-offs of waiting are likely depend on circumstances (e.g. pressure well-timed arrival, wind availability travelling with/without juvenile brood), migratory behaviour during barrier crossings is expected differ between seasons. We studied pink-footed geese Anser brachyrhynchus crossing the Barents Sea (ca 650 km), in spring autumn 2018–2020, using 94 GPS-tracks 38 individuals, with annotated ERA5 weather data. found that 1) especially autumn, selected departure; 2) spring, experienced lower support more crosswinds than leading 23% longer routes, 60% durations, 93% air distances 45% higher ratios air-to-ground distances; 3) both seasons, had tailwinds first part crossings, when deviating from shortest route; 4) stopped often (mean 11×) (3×), earlier stages but spent half time sea, which they still continued approach their destination slowly; 5) stops happened mostly adverse winds, warmer air, humidity calmer water and, took brood. conclude migrating geese, Arctic capital breeders, importance energy shift en route seasonal differences support, flying stopping a arrival cause autumn.