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

Background Unlike 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.

Methods We 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).

Results The 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.

Conclusions Our 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.