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

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.