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Summer 2012

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

July 17, 2012

The eastern cottontail way to chill

A heat wave may inspire some of us to crank up the AC and take a nap while the temperature spikes. Eastern cottontails do the same, but they use their own built-in cooling systems.

The solitary mammal restricts most of its activity to dawn and dusk, when it feeds on grasses, plantains, clover and garden vegetables. During the heat of the day, cottontails retreat to thickets, brush piles and hollow logs.

Rabbits use several strategies to regulate their body temperature, which becomes elevated on hot days. They have very few sweat glands (the fur coat prevents evaporation from the skin), so they use their ears as radiators.

Blood vessels in the ears dilate, allowing excess heat to dissipate from their large surface area. On very hot days, if the rabbit's body temperature approaches that of the surrounding air, its ears are no longer able to radiate heat, so the rabbit stretches out on the ground to release as much heat as possible from its body, and it begins to pant through its nose.

A panting rabbit increases its heart rate and breathing rate as blood is pumped through large, complex nasal passages, where inhaled air evaporates water from mucous membranes, cooling the area as the humid air is pulled into the lungs. Warmer exhaled air condenses some of its moisture onto the relatively cooler nasal passages, helping to conserve the rabbit's water.

Although rabbit ears may lose their ability to dump heat on record-hot days, they remain sensitive to the sounds of the animal's many predators, the advance of which inspires a bounding, zigzag escape into a nearby briar patch.

Eastern cottontail, Sylvilagus floridanus

Sources: University of Michigan Museum of Zoology, Acta Neurobiologiae Experimentalis, ciheam.org