| Kangaroo rats | ||||||||||||||
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| Scientific classification | ||||||||||||||
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Kangaroo rats are small rodents native to North and Central America. The name derives from their bipedal form (they hop like tiny kangaroos) but the resemblence is purely visual: kangaroo rats and kangaroos are not related, other than in that both groups are mammals.
There are 21 species, all in the genus Dipodomys. Size varies from 100 to 200 mm, with a tail of equal or slightly greater length; weight can be anywhere between 35 and 180 grams. The most distinctive feature of the kangaroo rats is their very long, hind legs.
Like the jerboas of African and Asian deserts and the hopping mice of outback Australia, kangaroo rats have highly developed hind legs, live in deep burrows which shelter them from the worst of the desert heat, and rarely drink water. Instead, they have a highly water-efficient metabolisim (their kidneys are at least four times more efficient than those of humans), and manufacture water by chemical breakdown of their food. Despite sharing so many characteristics with jerboas and hopping mice, the three groups are not closely related to one another: the similarities are the result of convergent evolution.
Kangaroo rats are found in arid and semi-arid areas of the United States and Mexico which retain some grass or other vegetation. Their diet includes seeds, leaves, stems, buds, some fruit, and insects. Most kangaroo rat species use their burrows and buried caches nearby to store food against the possibility of bad seasons. The Banner-tailed Kangaroo Rat has been recorded making burrows with several storage chambers up to 25 cm in diameter each, and containing almost 6 kilograms of stored food.
Unlike the jerboas and hopping mice, but like their close relatives the pocket mice, kangaroo rats have large cheek pouches that open on either side of the mouth and extend back to the shoulders. They fill the pouches with food or nesting material ready for transport back to the burrow, then empty them by turning them inside out, like pockets, with their forpaws. There is a special muscle that, once the pouch is empty and clean, pulls it back in again.
The overall colour of the kangaroo rats can be anywhere between pale sandy yellow and dark brown, with a white underside and often with white banding across the thighs. Tails tend to be dark with white sides and a tuft of longer hairs. Facial markings vary from one species to another, but all have an oil gland between the shoulders.