The gular sack of nightjars helps to dissipate heat efficiently by vibrating.
Image: Emily Harrington / EH Illustration / Copyright © - All rights reserved

The gular sac is rapidly expanded to increase the speed of air moving through the sac and buccal cavity. As the fast air passes, heat moves from the blood vessels close to the surface (convective heat loss) and also through the moist membranes (evaporative heat loss).

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Gular flutter demonstrated by a blue heron chick.

Last Updated October 14, 2016