Energy conversion efficiency peaks at intermediate flight speed in a migratory songbird

Area of Science:

• Ornithology
• Bioenergetics
• Biomechanics

Background:

• Flight is crucial for bird locomotion, especially migration, necessitating an understanding of energy use.
• Flight mechanical power (P_mech) and flight metabolic power (P_met) are key metrics in avian energetics.
• Energy conversion efficiency (η) links P_mech and P_met but has been difficult to measure directly, often assumed constant.

Purpose of the Study:

• To directly measure in vivo energy conversion efficiency (η) in birds during flight.
• To determine how η varies with flight speed in thrush nightingales.
• To provide empirical data for refining models of bird flight power.

Main Methods:

• Utilized the 13C-labeled sodium bicarbonate method for direct measurement of flight metabolic power (P_met).
• Employed particle image velocimetry to quantify flight mechanical power (P_mech).
• Conducted experiments with thrush nightingales in a wind tunnel across various flight speeds.

Main Results:

• Energy conversion efficiency (η) was found to vary as a concave function of flight speed.
• A maximum η of 15.3% was observed at flight speeds between 7-8 m/s.
• These optimal speeds are ecologically relevant for bird flight and migration.

Conclusions:

• Avian energy conversion efficiency (η) is speed-dependent, not constant.
• Birds appear to optimize their flight performance at specific, ecologically relevant speeds.
• These findings have significant implications for accurately modeling bird flight energetics and power requirements.