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Large ears used to cool off: jackrabbit

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Black-tailed Jackrabbit / Jerry Oldene.. / LicenseCC-by-nc-sa - Attribution Non-commercial Share Alike

The large ears of the jackrabbit are used in cooling, radiating heat via an extensive network of blood vessels.

FUNCTION
Summary
Jackrabbits live in the desert, where they're exposed to extremely hot daytime temperatures. But, these animals are able to stay cool by releasing excess heat from their oversized ears.  

The jackrabbit’s large ears provide an expansive surface area of exposed skin loaded with blood vessels. When the surrounding air temperature is slightly below the rabbit’s body temperature, as when it retreats from hot desert sun into shade, the blood vessels in the outer part of its ears widen in a process called vasodilation. This results in greater circulation of warm blood from the body’s core to the jackrabbit’s ears, where heat is lost to the cooler surrounding air. 

This cooling mechanism based on blood circulation helps to prevent overheating and maintain the jackrabbit’s body temperature within set boundaries. It’s also an important water conservation technique given the jackrabbit's arid habitat, as it reduces the need for evaporative cooling mechanisms, such as panting or sweating, which involve the loss of water. At air temperatures around 30° Celsius, convection from the jackrabbit's ears can shed all of the animal’s excess heat.

This summary was contributed by Ashley Meyers.
Excerpt
"Blood flow to the ear pinnae [outside portion of the ear] is curtailed at ambient temperatures of between 1.4° and 24.0° C, which minimizes heat loss across the pinnae and allows the surfaces of erect pinnae to approach ambient temperature. The pinnae are warmed by steady or pulsatile vasodilation in some animals when the ambient temperature is between 1° and 9° C below body temperature, a response favoring heat loss. When ambient temperature exceeds body temperature by 4° to 5° C, the pinnae are circulated with blood cooler than ambient temperature; this response favors heat influx." (Hill and Vegth 1976:436)

"Convection from the ears...could account for the loss of over 100% of the animal's metabolic heat at an air temperature of 30°C. If air temperature exceeds body temperature, the animal must either store heat or resort to the evaporation of water." (Wathen et al 1971:1030)

"Many desert animals have large ears, and the jack rabbit is no exception. It has been suggested that large ears, with their network of blood vessels, may serve to radiate heat to the sky while the animal is resting in the shade, so helping to lower its body temperature." (Foy and Oxford Scientific Films 1982:165)
About the inspiring organism
black-tailed jack rabbit
Lepus californicus Gray, 1837
Common name: Black-tailed Jackrabbit

Habitat(s): Artificial - Terrestrial, Desert, Grassland, Savanna, Shrubland
Learn more at EOL.org
Some organism data provided by: ITIS: The Integrated Taxonomic Information System
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

Threat Categories LONG_LC IUCN Red List Status: Least Concern

Bioinspired products and application ideas

Application Ideas: Heat collectors for buildings that are raised for nighttime cooling, building designs that funnel excess heat to a single room, extendable parts to cool electronics in sleep mode.

Industrial Sector(s) interested in this strategy: Building, architecture, electronics

References
Foy S; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
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Wathen P; Mitchell JW; Porter WP. 1971. Theoretical and experimental studies of energy exchange from jackrabbit ears and cylindrically shaped appendages. Biophysical Journal. 11(12): 1030-1047.
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Hill RW; Vegthe JH. 1976. Jackrabbit ears: surface temperatures and vascular responses. Science. 194(4263):
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Mohler FS; Heath JE. 1988. Comparison of IR thermography and thermocouple measurement of heat loss from rabbit pinna. American Journal of Physiology - Regulatory Integrative and Comparative Physiology. 254(2): 389-395.
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Hill, Richard W.; Christian, Donald P.; Veghte, James H. 1980. Pinna Temperature in Exercising Jackrabbits, Lepus californicus. Journal of Mammalogy. 61(1): 30-38.
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Comments

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Sherry
over 5 years ago
Thanks to Duarte Miguel Prazeres for finding and uploading a photo of a rabbit for this strategy.
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