Adjustments of wingbeat frequency and air speed to air density in free-flying migratory birds

Schmaljohann, Heiko; Liechti, Félix

doi:10.1242/jeb.031435

Cited by 42 publications

(21 citation statements)

References 59 publications

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“…). Furthermore, some birds will increase air speed at higher altitudes due to lower air pressure (Schmaljohann & Liechti ). This will mean that the difference between lower and higher altitudes we found is possibly even more pronounced.…”

Section: Discussionmentioning

confidence: 99%

“…Generally, higher altitudes have stronger winds but their predictability is less clear (Liechti 2006;Shamoun-Baranes et al 2010). Furthermore, some birds will increase air speed at higher altitudes due to lower air pressure (Schmaljohann & Liechti 2009). This will mean that the difference between lower and higher altitudes we found is possibly even more pronounced.…”

Section: Discussionmentioning

confidence: 99%

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Global aerial flyways allow efficient travelling

et al. 2015

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Birds migrate over vast distances at substantial costs. The highly dynamic nature of the air makes the selection of the best travel route difficult. We investigated to what extent migratory birds may optimise migratory route choice with respect to wind, and if route choice can be subject to natural selection. Following the optimal route, calculated using 21 years of empirical global wind data, reduced median travel time by 26.5% compared to the spatially shortest route. When we used a time-dependent survival model to quantify the adaptive benefit of choosing a fixed wind-optimised route, 84.8% of pairs of locations yielded a route with a higher survival than the shortest route. This suggests that birds, even if incapable of predicting wind individually, could adjust their migratory routes at a population level. As a consequence, this may result in the emergence of low-cost flyways representing a global network of aerial migratory pathways.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Global aerial flyways allow efficient travelling

et al. 2015

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“…Airspeeds were also converted to equivalent airspeeds at sea‐level pressure to account for air density effects (see section 3.4 in Pennycuick and Eq. 10 in Schmaljohann and Liechti ). To alleviate potential inaccuracies of the GPS measurements, altitudes and resultant airspeeds were smoothed using a 5‐span moving average.…”

Section: Methodsmentioning

confidence: 97%

Directed flight and optimal airspeeds: homeward‐bound gulls react flexibly to wind yet fly slower than predicted

McLaren

Shamoun‐Baranes

Camphuysen

et al. 2016

Journal of Avian Biology

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Birds in flight are proposed to adjust their body orientation (heading) and airspeed to wind conditions adaptively according to time and energy constraints. Airspeeds in goal-directed flight are predicted to approach or exceed maximum-range airspeeds, which minimize transport costs (energy expenditure per unit distance) and should increase in headwinds and crosswinds. Diagnosis of airspeed adjustment is however obscured by uncertainty regarding birds' goal-directions, transport costs, interrelations with orientation strategy and the attainability of predicted behaviour. To address these issues, we tested whether gulls minimized transport costs through adjustment of airspeed and heading to wind conditions during extended inbound flight over water (180-360 km) to their breeding colony, and introduce a methodology to assess transport (energy) efficiency given wind conditions. Airspeeds, heading, flight mode and energy expenditure were estimated using GPS tracking, accelerometer and wind data. Predicted flight was determined by simulating each trip according to maximum-range airspeeds and various orientation strategies. Gulls employed primarily flapping flight (93%), and negotiated crosswinds flexibly to exploit both high altitude tailwinds and coastal soaring opportunities. We demonstrate that predicted airspeeds in heavy crosswinds depend strongly on orientation strategy and presumed preferred direction. Measured airspeeds increased with headwind and crosswind similarly to maximum-range airspeeds based on full compensation for wind drift, yet remained ∼ 30% lower than predicted by all strategies, resulting in slower and 30-35% costlier flight. Interestingly, more energy could be saved through adjustment of airspeed (median 40%) than via orientation strategy (median 4%). Therefore, despite remarkably flexible reaction to wind at sea, these gulls evidently minimized neither time nor energy expenditure. However, airspeeds were possibly over-predicted by current aerodynamic models. This study emphasizes the importance of accounting for orientation strategy when assessing airspeed adjustments to wind and indicates that either the cost or adaptive 'currency' of extended flight among gulls may require revision.

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“…One of the main challenges is the ability to measure flight mode and wing beat kinematics during migration. Tracking radar has been used for short distances to show how birds adjust flight mode (Spaar and Bruderer 1997) to atmospheric conditions and flight kinematics to air density (Schmaljohann and Liechti 2009). Biologging, specifically accelerometers, can be used to identify flight mode as well as flight kinematics for entire migration journeys (Liechti et al 2013; Hedenström et al 2016; Rotics et al 2016; Shamoun-Baranes et al 2016a).…”

Section: Individual Responsementioning

confidence: 99%

Atmospheric conditions create freeways, detours and tailbacks for migrating birds

2017

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The extraordinary adaptations of birds to contend with atmospheric conditions during their migratory flights have captivated ecologists for decades. During the 21st century technological advances have sparked a revival of research into the influence of weather on migrating birds. Using biologging technology, flight behaviour is measured across entire flyways, weather radar networks quantify large-scale migratory fluxes, citizen scientists gather observations of migrant birds and mechanistic models are used to simulate migration in dynamic aerial environments. In this review, we first introduce the most relevant microscale, mesoscale and synoptic scale atmospheric phenomena from the point of view of a migrating bird. We then provide an overview of the individual responses of migrant birds (when, where and how to fly) in relation to these phenomena. We explore the cumulative impact of individual responses to weather during migration, and the consequences thereof for populations and migratory systems. In general, individual birds seem to have a much more flexible response to weather than previously thought, but we also note similarities in migratory behaviour across taxa. We propose various avenues for future research through which we expect to derive more fundamental insights into the influence of weather on the evolution of migratory behaviour and the life-history, population dynamics and species distributions of migrant birds.

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Adjustments of wingbeat frequency and air speed to air density in free-flying migratory birds

Abstract: SUMMARY

Cited by 42 publications

References 59 publications

Global aerial flyways allow efficient travelling

Global aerial flyways allow efficient travelling

Directed flight and optimal airspeeds: homeward‐bound gulls react flexibly to wind yet fly slower than predicted

Atmospheric conditions create freeways, detours and tailbacks for migrating birds

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