By Dimitri Smirnoff and Jeanette Lim
If you lived in Death Valley, how would you stay cool?
In a place where summer temperatures average a staggering 46˚ C (116˚ F) staying cool can be a challenge for any critter! Humans have evolved to produce sweat, which takes away heat when it evaporates in the air. However, Death Valley only receives about 6 centimeters (2.4 inches) of rain every year. Animals that sweat would get dehydrated pretty quickly.
So how do animals in this arid environment stay cool? One mammal can cool its body using a strategy that requires no water loss at all. Black-tailed jackrabbits (which are actually hares) are common in American deserts, staying active during daytime hours despite the heat. Jackrabbits are famous for their disproportionately large ears, which happen to be their trick for staying cool.
The jackrabbit’s pinnae (the visible part of an animal’s ears) are packed with small blood vessels that carry hot blood from the body’s core. When the air temperature is slightly cooler than the hare’s body temperature, this difference in temperature causes heat to flow from the ears to the surrounding air. A jackrabbit’s big ears provide a large surface area for heat exchange. Furthermore, the blood vessels can widen (a process called vasodilation), allowing more warm blood to circulate to the ears for even greater heat loss. (This same process happens when your cheeks turn red during exercise!)
At air temperatures around 30° C (86° F), heat loss from the jackrabbit’s ears can shed all of the animal’s excess heat. Using its ears as radiators helps the jackrabbit maintain a safe body temperature while also retaining precious water that would have been lost through cooling mechanisms such as sweating or panting.
The jackrabbit is not the only creature to use appendages to manage excess heat. Opossums, rats, and muskrats exchange heat from their tails when they exercise, seals send blood to their flippers, and goats can stay cool with the help of their horns. But few would dispute that the jackrabbit faces some of the most extreme temperature-regulation challenges in its Death Valley home.
What can humans learn from this resourceful strategy?
The black-tailed jackrabbit’s strategy for heat loss could be applied to situations where overheating is a danger. For example, server farms keep the Internet running, but they also generate a lot of heat, with some consuming as much electricity as 180,000 homes. Could the jackrabbit from Death Valley have something to teach humans in Silicon Valley? Or perhaps the jackrabbit’s strategy could inform more sustainable designs for home air conditioners. Beyond buildings, many devices, such as engines, machinery, and electronics are damaged by overheating and must be cooled? How might they benefit from the jackrabbit’s cool strategy?
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More to learn and do!
Interested in classroom activities related to biomimicry? Find free resources on the Biomimicry Institute’s Biomimicry Education Network.
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Dimitri Smirnoff obtained his B.A. in biology from Carleton College and is currently pursuing a Master’s in biomimicry at Arizona State University. He is passionate about communicating biological information to non-biologists to aid them in generating more sustainable and innovative solutions to human design challenges.
Jeanette Lim is the AskNature content coordinator and gets to share her love of biology with other nature enthusiasts. Her favorite place to explore is the rocky intertidal zone.