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Kangaroo rats
Last updated on Wednesday, January 01, 2003
After dropping Molly at summer school classes one morning, Richard and I spotted a kangaroo rat lying by the side of Picacho Avenue in Las Cruces. It must have been recently hit by a car; its pale gold and white fur looked fresh, and the black tuft at the tip of its long tail stirred slightly in the rush of air from the passing traffic.
Kangaroo rats are not rats at all; nor are they kangaroos. These rodents are so named because they look like tiny kangaroos, with an upright, hopping gait, huge hind legs and feet, and a long, furry tail which comprises nearly two-thirds of their foot-or-so total length.
Bipedal locomotion serves these desert residents well, both for nocturnal foraging and for escaping predators. When pursued, a kangaroo rat pushes off swiftly with those big hind legs and leaps in a wild, randomly zigzagging flight much like a bouncing Superball, changing course quickly by swinging its long, rudderlike tail, and springing up to ten feet at a leap.
Kangaroo rats are the ³desert rats² of the rodent order, superbly adapted to this arid country. Elaborate physiological and behavioral adaptations allow them to survive without ever drinking water.
Elongated nasal passages cool their outgoing breath and recapture its moisture. Super-efficient kidneys save water also, concentrating salts and urea from ten to twenty times before eliminating them.
Even kangaroo rats¹ feces are concentrated, containing 50 percent less water than human feces. Further, kangaroo rats forage in the cooler, wetter nighttimes, spending the hottest hours underground in climate-controlled burrows. They derive what little water that they need from metabolizing the carbohydrates in their food.
Bipedal locomotion also helps kangaroo rats save water by minimizing the time and energy that they spend foraging. These big-eyed rodents hop across the desert at night on their hind legs, keeping their front paws free to pick up food - plant seeds.
Instead of stopping to eat, they stuff the seeds into their ³shopping bags,² fur-lined cheek pouches along their lower jaws which can hold about a teaspoon apiece. When their cheek pouches are crammed full, kangaroo rats hop back to their burrows to either store their stash or munch their meal in peace, safe from the many nighttime predators.
Kangaroo rats are well-adapted to nocturnal life. Their big head - equal to one-third of their body - allows space for an inflated middle-ear echo chamber that magnifies sounds, enabling them to easily hear predators like owls and rattlesnakes. Extra-large eyes placed high on their head give them acute night vision.
Unfortunately, although kangaroo rats are elegantly adapted to the harsh desert environment, they are not prepared for urban life. Many, like the bannertail kangaroo rat that we spotted dead on Picacho Avenue, are struck by cars while crossing roads at night; others are killed by free-roaming cats.
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