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Summer 2010

Urban Jungle

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

July 27, 2010

The brown rat

D.C.’s second-most-successful mammal

Summer provides an abundance of food and vegetation that supports a seasonally swelling population of brown rats.

"Spring and summer are the peak breeding seasons," says D.C. Department of Health spokeswoman Dena Iverson. "Winter acts as a natural exterminator: When it's cold, rats become stressed and breeding is reduced."

Unless they're held in captivity, rats live only about a year, so they reproduce early and often.

A rat born in May could already be raising a litter of her own by July. It's possible that she was impregnated again only 10 hours after giving birth and could be expecting another 10 pups before August.

District residents can help curb the rat population by securing garbage, taking uneaten pet food back indoors, clearing the yard of weeds and junk, and restricting rat access to buildings by plugging up any hole larger than the circumference of a quarter. Rats love seeds, so your bird feeder may be attracting more than just doves, sparrows and cardinals.

For help with rodent control, dial the Citywide Call Center at 311.


An omnivorous rodent

In addition to dining on human refuse, rats will eat birds, mice, amphibians, small reptiles, fish, eggs, carrion, pet feces, insects, mollusks, worms, leaves, roots, tubers, wood, bark, stems, seeds, nuts, grains, fruits, nectar, flowers, sap and fungi. If poisoned, rats will swallow clay, which absorbs toxins.

Sources: everyblock.com; D.C. Department of Health; ratbehavior.org; University of Michigan Museum of Zoology

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Map by Mary Kate Cannistra/The Washington Post

Brown rat, Rattus norvegicus