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Drink safely: common swifts (Apus apus) dissipate mechanical energy to decrease flight speed before touch-and-go

Geoffrey Ruaux¹, Kyra Monmasson¹, Tyson L Hedrick²

¹Univ Rennes, Normandie Univ, CNRS, EthoS (Éthologie animale et humaine) - UMR 6552, F-35000 Rennes, France.

The Journal of Experimental Biology

|February 22, 2023

Summary

Common swifts (Apus apus) surprisingly brake before drinking, dissipating energy instead of conserving it. This costly behavior may prioritize safety over energy efficiency during aerial drinking maneuvers.

Keywords:

Air-brake Kinematics Wind

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Area of Science:

Ornithology
Biomechanics
Animal Behavior

Background:

Birds face selective pressure to reduce flight energy expenditure.
Common swifts (Apus apus) are highly aerial, performing activities like drinking in flight.
Touch-and-go drinking could be energy-saving by converting potential to kinetic energy.

Purpose of the Study:

To investigate the energy expenditure and mechanics of drinking in common swifts.
To test the hypothesis that swifts conserve mechanical energy during aerial drinking.

Main Methods:

3D optical tracking of 163 swift drinking trajectories near Rennes, France.
Analysis of swift movement and energy dynamics before water contact.

Main Results:

Contrary to energy conservation, swifts with higher mechanical energy did not reach water at higher speeds.
Swifts actively braked, dissipating mechanical energy by losing height and speed.
Braking was associated with sharp turns and potentially headwind, with finer adjustments also possible.

Conclusions:

Common swifts exhibit a surprisingly energy-dissipating behavior during drinking.
This costly braking likely represents a trade-off between energy expenditure and safety.
High speed increases the risk of falling into water, incurring significant energetic and survival costs.