Seasonally specific responses to wind patterns and ocean productivity facilitate the longest animal migration on Earth

Abstract

Migratory strategies of animals are broadly defined by species’ eco-evolutionary dynamics, while behavioural plasticity according to the immediate environmental conditions en route is crucial for energy efficiency and survival. The Arctic tern Sterna paradisaea is known for its remarkable migration capacity, as it performs the longest migration known by any animal. Yet, little is known about the ecology of this record-breaking journey. Here, we tested how individual migration strategies of Arctic terns are adapted to wind conditions and fuelling opportunities along the way. To this end, we deployed geolocators on adult birds at their breeding sites in Svalbard, Norway. Our results confirm fundamental predictions of optimal migration theory: Arctic terns tailor their migration routes to profit from (1) tailwind support during the movement phase and (2) food-rich ocean areas during the stopover phase. We also found evidence for seasonally distinct migration strategies: terns prioritize fuelling in areas of high ocean productivity during the southbound autumn migration and rapid movement relying on strong tailwind support during the northbound spring migration. Travel speed in spring was 1.5 times higher compared to autumn, corresponding to an increase in experienced wind support. Furthermore, with their pole-to-pole migration, Arctic terns experience approximately 80% of all annual daylight on Earth (the most by any animal), easing their strictly diurnal foraging behaviour. However, our results indicate that during migration daylight duration is not a limiting factor. These findings provide strong evidence for the importance of interaction between migrants and the environment in facilitating the longest animal migration on Earth.

Six pelagic seabird species of the North Atlantic engage in a fly-and-forage strategy during their migratory movements

“…5 & S4). Similar results have been found in previous studies on the same species (Hatch et al 2010, Frederiksen et al 2012, Mosbech et al 2012, Fayet et al 2016, Merkel et al 2021 and in many other seabird species such as Arctic terns, long-tailed skuas, sooty shearwaters and wandering albatrosses (Shaffer et al 2006, Weimerskirch et al 2015, van Bemmelen et al 2017, Hromádková et al 2020. Seabird migration patterns therefore did not match the dispersive migration definition (Newton 2007).…”

“…In particular, birds reaching the North-West Atlantic travelled along South-East Greenland in the autumn and came back by crossing the Atlantic Ocean south from Iceland. These routes are likely to follow wind and current regimes, which may reduce the energetic costs of migration and ultimately shape the geographic distribution of birds in the non-breeding season (Adams & Flora 2010, Hromádková et al 2020. The fact that several species share the same migration routes also increases the need to consider protection of 'migratory corridors' as a broader ecosystem unit rather than species-specific routes and areas.…”

Seasonal variations in migration strategy of a longdistance Arctic-breeding seabird

“…This pattern differs from other seabirds that follow similar migratory paths. For instance, Arctic terns migrate 1.5 times faster in spring than in fall while covering similar distances (Egevang et al 2010, Hromádková et al 2020. The slower travel speed in spring and the higher number of daily immersions (more time in contact with saltwater) compared to fall provide evidence that jaegers adopt some sort of flyand-forage migration strategy in spring (Strandberg & Alerstam 2007).…”

Foraging on the wing for fish while migrating over changing landscapes: traveling behaviors vary with available aquatic habitat for Caspian terns

“…In particular, successful animal migration should depend on how individuals adjust behaviors between and within seasons [ 2 ], because changing behaviors as weather and ecological variables vary along the route can reduce the costs of migration [ 3 , 4 ] and even lead to the avoidance of hazardous weather events to ensure survival [ 5 ]. Although mechanistic explanations of decision-making remain unclear [ 6 ], research on birds has shown that individuals can select favorable winds [ 5 , 7 , 8 ], weather [ 9 , 10 ], flight altitudes [ 11 ], routes [ 12 , 13 ] and stopover frequency [ 14 ] and sites [ 15 , 16 ]. Between years, changes in migratory timing for several species have also been documented [e.g.…”