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

Abstract

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

Migratory swans individually adjust their autumn migration and winter range to a warming climate

“…Our GPS‐tracked birds moved larger daily distances with beneficial winds during early autumn, an effect in the same order of magnitude as that of temperature. Wind assistance can drive higher daily distances through increasing the daily departure probability (Geisler et al, 2022; Klaassen et al, 2004; Kölzsch et al, 2016; Xu & Si, 2019) but also through facilitating faster ground speed when in flight (Kemp et al, 2010). The declining effects of temperature and wind assistance on movement throughout autumn indicate that the birds become less responsive to those climatic factors towards their eventual winter range, likely due to coming closer to and eventually reaching a geographical area that is considered a potential wintering area based on experience or social information (see Abrahms et al, 2021).…”

“…Like many waterfowl species (Geisler et al, 2022;Kölzsch et al, 2016; Xu & Si, 2019), Bewick's swans make use of favourable winds to facilitate their migration (Beekman et al, 2002;Evans, 1979;Klaassen et al, 2004). Five-yearly international population censuses indicated that more Bewick's swans winter further north in warmer winters (Beekman et al, 2019).…”

“…Its autumn migration proceeds faster than its spring migration because in spring ice cover restricts northward travel (Nuijten et al, 2014) and birds capitalize on bringing the energy stores required for breeding with them to the breeding grounds (capital breeding; Nolet, 2006). Like many waterfowl species (Geisler et al, 2022; Kölzsch et al, 2016; Xu & Si, 2019), Bewick's swans make use of favourable winds to facilitate their migration (Beekman et al, 2002; Evans, 1979; Klaassen et al, 2004). Five‐yearly international population censuses indicated that more Bewick's swans winter further north in warmer winters (Beekman et al, 2019).…”

How birds dissipate heat before, during and after flight

“…Supporting this suggestion are measurements made on wild birds. For example, at higher air temperatures pink-footed geese ( Anser brachyrhynchus ; [ 35 ]) are less likely to fly, godwits ( Limosa limosa ; [ 36 ]), great reed warblers ( Acrocephalus arundinaceus ; [ 37 ]) and great snipe ( Gallinago media ; [ 38 ]) fly at higher altitudes and hyperthermia in common eiders ( Somateria mollissima ), has been suggested to explain their use of stopovers [ 39 ].…”

Multi‐colony tracking of two pelagic seabirds with contrasting flight capability illustrates how windscapes shape migratory movements at an ocean‐basin scale

“…flapping, glide‐flapping or soaring), their body mass, aspect ratio (wing length divided by wing width) and wing loading (body mass divided by the area of the wing) (Bowlin and Wikelski 2008, Horton et al 2018). Migrants can further adjust their behaviour to wind conditions by waiting for optimal wind conditions to engage in migration (Gill et al 2009), selecting an altitude with favourable winds (Mateos‐Rodríguez and Liechti 2012), or, when possible, landing and waiting when winds are unfavourable (Shamoun‐Baranes et al 2017, Geisler et al 2022). Furthermore, if the prevailing winds are stable throughout the year, wind conditions along a given route are likely to be more favourable during either the outbound or the inbound migration.…”