The role of wingbeat frequency and amplitude in flight power

Abstract

Body-mounted accelerometers provide a new prospect for estimating power use in flying birds, as the signal varies with the two major kinematic determinants of aerodynamic power: wingbeat frequency and amplitude. Yet wingbeat frequency is sometimes used as a proxy for power output in isolation. There is, therefore, a need to understand which kinematic parameter birds vary and whether this is predicted by flight mode (e.g. accelerating, ascending/descending flight), speed or morphology. We investigate this using high-frequency acceleration data from (i) 14 species flying in the wild, (ii) two species flying in controlled conditions in a wind tunnel and (iii) a review of experimental and field studies. While wingbeat frequency and amplitude were positively correlated, R 2 values were generally low, supporting the idea that parameters can vary independently. Indeed, birds were more likely to modulate wingbeat amplitude for more energy-demanding flight modes, including climbing and take-off. Nonetheless, the striking variability, even within species and flight types, highlights the complexity of describing the kinematic relationships, which appear sensitive to both the biological and physical context. Notwithstanding this, acceleration metrics that incorporate both kinematic parameters should be more robust proxies for power than wingbeat frequency alone.

Turbulence causes kinematic and behavioural adjustments in a flapping flier

“…We identified individual wingbeats following [ 28 ]. In summary, we smoothed the raw heave values over 20 events to remove the high frequency noise from the heave signal.…”

“…We used the amplitude of the heave acceleration as a proxy for wingbeat amplitude [ 28 ]. This approach is based on the correlation between body acceleration signal and wing displacement within a wingbeat cycle.…”

“…From here on, the term ‘wingbeat amplitude' therefore refers to the amplitude of the heave signal. The heave amplitude was calculated as the difference between the peak and the trough of the raw heave values within a single wingbeat cycle [ 28 ].…”

On the role of tail in stability and energetic cost of bird flapping flight

“…) ν = (β, ψ s,z , A s,x , q w,y ) www.nature.com/scientificreports/ amplitude A s,x has a direct impact on thrust production and therefore on airspeed and power consumption 38 .…”

Flight performance, activity and behaviour of breeding pied flycatchers in the wild, revealed with accelerometers and machine learning

“…Bird flight behaviours have been studied for many years, including detailed examinations of flight kinematics (e.g., Hedenström and Møller, 1997, Krishnan et al, 2022), aerodynamics (e.g., Muijres et al, 2012a, Alerstam et al, 2007) and general aspects such as migration flight strategies (e.g., Mitchell et al, 2015, Jiguet et al, 2019). Despite this, still very little is known about the fundamental aspects of what is required from a bird in terms of flight performance in their day-to-day lives during routine transport flights and foraging flights.…”