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  • Strategy

Gular fluttering dissipates heat: nightjars


Gular flutter cooling mechanism / Emily Harrin.. / LicenseCopyright - All Rights Reserved

The gular sack of nightjars helps to dissipate heat efficiently by vibrating.

"An important environmental adaptation for many caprimulgiformes is the ability to withstand high ambient temperature (Ta). Birds of this order are most common in warm climates, and frogmouths, potoos, and nightjars all roost and nest in the open where they can be subjected to long periods of direct sun exposure. In these circumstances, they avoid hyperthermia by using evaporative cooling strategies. Nightjars dissipate heat by gular fluttering, during which the mouth is opened, the rate of blood flow to the buccal area is increased, and the moist gular area is rapidly vibrated." (Fowler and Miller 2003: 225)

"When poorwills are exposed to high temperatures, they increase evaporation of water by initiation of gular flutter and by some increase in breathing rate. Gular flutter supplements evaporation due to respiration, and involves a rapid vibration of the moist membranes of the gular region, driven by the hyoid. The rate of gular flutter in the poorwill is relatively constant and independent of heat load, and evaporation due to flutter is modulated by varying the amount of time spent fluttering, as well as the amount of air moved per flutter." (Lasiewski 1969:1504)

Watch Video (doesn't show gular fluttering, but beautiful!)

Watch Video (gular fluttering of a heron chick)

Gular flutter cooling mechanism. 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). Artist: Emily Harrington. Copyright: All rights reserved. See gallery for details.

About the inspiring organism

Learn more at
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

Bioinspired products and application ideas

Application Ideas: In dry hot climates, use of moist mesh material that vibrates to create evaporative cooling could be used to cool housing or building sites.

Industrial Sector(s) interested in this strategy: Air conditioning,

Fowler, ME; Miller, RE. 2003. Zoo and Wild Animal Medicine. Philadelphia: W.B. Saunders Co.
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Lasiewski RC. 1969. Physiological responses to heat stress in the poorwill. American Journal of Physiology. 217(5): 1504-1509.
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Sturkie PD; Whittow GC. 2000. Avian physiology. Ithaca, NY: Cornell University Press. 685 p.
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over 5 years ago
Thanks to Emily Harrington for the illustration about how the gular fluttering works.
over 6 years ago
Thanks to Duarte Miguel Prazeres for finding and uploading this photo. Despite looking in many places, I haven't been able to find a photo showing the gular sack!
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