A comparison of flight energetics and kinematics of migratory Brambling and residential Eurasian Tree Sparrow

Yang Wang,Zhipeng Ren,Dongming Li,Ghulam Nabi,Juyong Li,Yuefeng Wu,Yanfeng Sun,Yuan Yin,Chuan Jiang

doi:10.1186/s40657-020-00211-y

Abstract

BackgroundUnlike resident birds, migratory birds are generally believed to have evolved to enhance flight efficiency; however, direct evidence is still scarce due to the difficulty of measuring the flight speed and mechanical power.MethodsWe studied the differences in morphology, flight kinematics, and energy cost between two passerines with comparable size, a migrant (Fringilla montifringilla, Brambling, BRAM), and a resident (Passer montanus, Eurasian Tree Sparrow, TRSP).ResultsThe BRAM had longer wings, higher aspect ratio, lower wingbeat frequency, and stroke amplitude compared to the TRSP despite the two species had a comparable body mass. The BRAM had a significantly lower maximum speed, lower power at any specific speed, and thus lower flight energy cost in relative to the TRSP although the two species had a comparable maximum vertical speed and acceleration.ConclusionsOur results suggest that adaptation for migration may have led to reduced power output and maximum speed to increase energy efficiency for migratory flight while residents increase flight speed and speed range adapting to diverse habitats.

Highlights

Unlike resident birds, migratory birds are generally believed to have evolved to enhance flight efficiency; direct evidence is still scarce due to the difficulty of measuring the flight speed and mechanical power
Considering that power consumption follows a U-shaped relationship with flight speed, fly at a speed too low or high than usual will demand an extra amount of energy and lower energy efficiency (Alerstam et al 2007; Wang et al Avian Res (2020) 11:25
Our results provided evidence that the migratory passerines exhibit a higher flight energy efficiency, especially at a lower speed range, and this functional improvement is evolved through the combined adaptive features of wing morphology and kinematics

Summary

Introduction

Migratory birds are generally believed to have evolved to enhance flight efficiency; direct evidence is still scarce due to the difficulty of measuring the flight speed and mechanical power. According to the theory of migration syndrome (Bauchinger et al 2005; Hedenström 2008), migratory birds have evolved a suite of modifications in wing morphology and kinematics in terms of energy consumption for long-journey flight than residents (Hedenström 2008; van Oorschot et al 2016). Small migratory birds should fly at speed with the maximum range speed (Vmr) and maximize the efficiency of flight to meet the strategy of energy-minimization during the flight (Hedenström 2002; Tobalske et al 2003). By measuring flight-related morphology, kinematics, and maximum weight lifted during maximum load-lifting flight trials, we can calculate aerodynamic power output with aerodynamic model and estimate flight speed (Vmr and Vmax). Vmr is calculated with flight-related morphology and optimized kinematics; Vmax is the maximal flight speed supported by maximal available output power in load-lifting flight trials (Pennycuick 2008). The minimal flight energy cost at a certain distance

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Discussion

Conclusion