Extreme altitude changes between night and day during marathon flights of great snipes

Lindström, Åke; Alerstam, Thomas; Andersson, Arne; Bäckman, Johan; Bahlenberg, Peter; Bom, Roeland A.; Ekblom, Robert; Klaassen, Raymond H. G.; Korniluk, Michał; Sjöberg, Sissel; J, Weber

doi:10.1016/j.cub.2021.05.047

Cited by 38 publications

(35 citation statements)

References 35 publications

(54 reference statements)

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“…The tracked nightjars reached altitudes just below 5000 masl, which is similar to recordings of another trans-Saharan migrant, the Eurasian hoopoe, Upupa epops , but considerably lower than the maximum flight altitudes above 6000 masl of great reed warblers, Acrocephalus arundiaceus ( Liechti et al, 2018 ; Sjöberg et al, 2021 ), and great snipes, Gallinago media (above 8000 masl; Lindström et al, 2021 ). The nightjars flew at the highest altitudes during the spring crossing of the Sahara desert, which conforms well with the general pattern of altitude distribution of avian migrants based on radar observations in Europe and west-Saharan Africa (reviewed in Bruderer et al, 2018 ).…”

Section: Discussionsupporting

confidence: 67%

“…This work adds to a list of recent studies reporting surprisingly extensive vertical movements within migratory flights, hinting at a presumably widespread migration pattern that remains poorly understood (e.g. Bowlin et al, 2015 ; Liechti et al, 2018 ; Lindström et al, 2021 ; Senner et al, 2018 ; Sjöberg et al, 2018 , 2021 ). Although near-level flight still made up a large fraction of the nightjars’ migratory flights (as revealed by the 5 min resolution data), it was commonly fragmented and intermixed with intermediate and large changes of altitude.…”

Section: Discussionmentioning

confidence: 58%

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Flight altitude dynamics of migrating European nightjars across regions and seasons

Norevik

Åkesson

Andersson

et al. 2021

Journal of Experimental Biology

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Avian migrants may fly at a range of altitudes, but usually concentrate near strata where a combination of flight conditions is favourable. The aerial environment can have a large impact on the performance of the migrant and is usually highly dynamic, making it beneficial for a bird to regularly check the flight conditions at alternative altitudes. We recorded the migrations between northern Europe and sub-Saharan Africa of European nightjars Caprimulgus europaeus to explore their altitudinal space use during spring and autumn flights and to test whether their climbs and descents were performed according to predictions from flight mechanical theory. Spring migration across all regions was associated with more exploratory vertical flights involving major climbs, a higher degree of vertical displacement within flights, and less time spent in level flight, although flight altitude per se was only higher during the Sahara crossing. The nightjars commonly operated at ascent rates below the theoretical maximum, and periods of descent were commonly undertaken by active flight, and rarely by gliding flight, which has been assumed to be a cheaper locomotion mode during descents. The surprisingly frequent flight-altitude shifts further suggest that nightjars can perform vertical displacements at a relatively low cost, which is expected if the birds can allocate potential energy gained during climbs to thrust forward movement during descents. The results should inspire future studies on the potential costs associated with frequent altitude changes and their trade-offs against anticipated flight condition improvements for aerial migrants.

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Section: Discussionsupporting

confidence: 67%

Section: Discussionmentioning

confidence: 58%

Flight altitude dynamics of migrating European nightjars across regions and seasons

Norevik

Åkesson

Andersson

et al. 2021

Journal of Experimental Biology

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“…This often entailed low-level flights over the Pacific Ocean, a strategy that has been documented in other shorebirds making transoceanic crossings [ 56 ], as well as dynamic altitude-switching, which may incur lower costs for nimble, long-winged godwits than for other larger-bodied species [ 57 ]. Other factors not included in our models, such as predation risk or thermoregulation, may have also influenced flight altitude [ 58 , 59 ], though our models suggest that their effects are likely minimal over much of this flight. Strong correlations between wind conditions at two favorable altitudes also underscore that we need not know the precise altitude at which a godwit was flying to approximate the wind conditions it was experiencing and classify its behavior.…”

Section: Discussionmentioning

confidence: 99%

Compensation for wind drift prevails for a shorebird on a long-distance, transoceanic flight

et al. 2022

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Background Conditions encountered en route can dramatically impact the energy that migratory species spend on movement. Migratory birds often manage energetic costs by adjusting their behavior in relation to wind conditions as they fly. Wind-influenced behaviors can offer insight into the relative importance of risk and resistance during migration, but to date, they have only been studied in a limited subset of avian species and flight types. We add to this understanding by examining in-flight behaviors over a days-long, barrier-crossing flight in a migratory shorebird. Methods Using satellite tracking devices, we followed 25 Hudsonian godwits (Limosa haemastica) from 2019–2021 as they migrated northward across a largely transoceanic landscape extending > 7000 km from Chiloé Island, Chile to the northern coast of the Gulf of Mexico. We identified in-flight behaviors during this crossing by comparing directions of critical movement vectors and used mixed models to test whether the resulting patterns supported three classical predictions about wind and migration. Results Contrary to our predictions, compensation did not increase linearly with distance traveled, was not constrained during flight over open ocean, and did not influence where an individual ultimately crossed over the northern coast of the Gulf of Mexico at the end of this flight. Instead, we found a strong preference for full compensation throughout godwit flight paths. Conclusions Our results indicate that compensation is crucial to godwits, emphasizing the role of risk in shaping migratory behavior and raising questions about the consequences of changing wind regimes for other barrier-crossing aerial migrants.

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“…Ideally, one would use wind data with a higher spatial and temporal resolution and include several measurements, each at its appropriate altitude, which would give a more precise picture of the wind conditions en route. et al, 2021;Meier et al, 2018;Liechti et al, 2018;Dhanjal-Adams et al, 2018). We focus on route inference with light-level geolocation.…”

Section: Discussionmentioning

confidence: 99%

“…Several recent studies have combined measurements from miniaturised multi‐sensor loggers, such as light, air pressure and activity to study the migratory movement of small birds (Åke Lindström et al, 2021; Meier et al, 2018; Liechti et al, 2018; Dhanjal‐Adams et al, 2018). We focus on route inference with light‐level geolocation.…”

Section: Discussionmentioning

confidence: 99%

Gone with the wind: Inferring bird migration with light‐level geolocation, wind and activity measurements

2022

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To investigate the complex phenomenon of bird migration, researchers rely on sophisticated methods for tracking long‐distant migrants. While large birds can be equipped with satellite tags, these are too heavy for many species. Instead, researchers often use light‐level geolocation for tracking individual small migratory birds. Unfortunately, light‐level geolocation is often coarse and unreliable, with positioning errors of anything up to hundreds of kilometres. Recent Bayesian models try to constrain the route to plausible corridors: they couple light‐level measurements with information about the bird's likely movement. While these models improve inference, they still lack information on weather conditions, specifically the impact of wind. For example, birds might encounter tailwinds—considerably increasing their (ground) speed and making longer routes more likely, or headwinds—having the opposite effect. Miniaturised multi‐sensor tags allow monitoring not only light but also acceleration and air pressure. These measurements provide essential additional information about the exact timing of flight activity and the corresponding flight altitudes. This article proposes a Bayesian model for inferring bird migration. The model integrates air pressure to estimate flight altitudes and considers wind data to calculate the most likely flight trajectory. The model constrains the migratory routes to those likely given by the winds en route and the observed timing of flight activity. We apply the model to infer the migration of European Hoopoes Upupa epops. Adding wind data for route inference excludes flight trajectories with unrealistic high airspeeds, decreases the uncertainty of the position estimates and returns more plausible migratory routes. Faithful reconstruction of migratory routes helps unravel the influence of physiological and environmental factors on bird migration. This is crucial for habitat protection where limited resources need to be allocated to relevant areas.

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Extreme altitude changes between night and day during marathon flights of great snipes

Cited by 38 publications

References 35 publications

Flight altitude dynamics of migrating European nightjars across regions and seasons

Flight altitude dynamics of migrating European nightjars across regions and seasons

Compensation for wind drift prevails for a shorebird on a long-distance, transoceanic flight

Gone with the wind: Inferring bird migration with light‐level geolocation, wind and activity measurements

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