Rodents

Bushy-tailed Wood Rat

Do Rodents Really Rule? Yes, if you go by the numbers. There are approximately 4,000 known mammal species on earth. Of that, 42% are rodents!


You don't get to be the most numerous mammal on the planet without some secret to success. And the rodents have a couple. To begin, they are prolific breeders, the absolute champions among mammals. Take the average harvest mouse, for example. Sexually mature at five months, she is capable of producing a litter of four pups every month. Even if she manages to live just a single year (the average for the species), she could potentially leave behind a progeny of over 50 harvest mice. Now consider that her children and her children's children are producing offspring at the same rate. Now notch it up a bit and think of this: Voles are sexually mature at 32 days!

The diminutive dimensions of most rodents is an advantage, too. Cover, camouflage and food all favor the small. Predominately vegetarian and adapted to a wide variety of foods, the rodent does not require large territories or great quantities of forage. Many practice winter hibernation or summer estivation, another advantage. Finally, man himself, with his penchant for open fields, farms, and trash has inadvertently created a rodent cornucopia.

 

To learn what a rodent is, read on. 

Much of this article was borrowed from John Regan, Northwest Wildlife Online 

Beaver

What Makes A Rodent A Rodent?

Opposing pairs of large incisors at the front of the upper and lower jaw are the most notable features. In fact, the word, "rodent" is from the latin, "to gnaw!" Worn down through a lifetime of industrious chewing, the teeth grow throughout the animal's life, and are continuously sharpened as they rub against each other. Some rodents, such as the porcupine and beaver, have hard, orange enamel on the fronts of their teeth and a softer white dentin on the backs. These surfaces wear at different rates, causing the four front teeth to self-sharpen into chisel-like cutting surfaces.

The vast majority of rodents are small and don't live a particularly long life. Their unremarkable bodies are fairly uniform and plain in color. Hovering at the bottom of the food chain they form the foundation of survival for many predators.

Rodent sizes. The South American capybara can grow to 4.3 feet in length and140 pounds. The fossil record shows rodents the size of cows, and one species that may have weighed as much as 2.5 tons. Now that's a whopping grand rodent!

At weights approaching 70 pounds, the North American beaver is not only Columbia NWR's largest rodent, but also one of the largest in the world. The North American porcupine fits into the large rodent category, too, at 40 pounds. The refuge's next-largest rodent is the yellow-bellied marmot that tops out at 11 pounds. In the mid-size range are muskrats, gophers, squirrels and chipmunks. Continuing down the size scale, we have a wide variety of kangaroo rats, mice and a generally little-known group of rodents called voles. As a family, the voles, sometimes called pocket mice, are the smallest rodents in our region.

 

Interested in rodent behavior? That's the next section. 

Pocket Gopher Esker

Why Don't I See More Rodents?

Numerous though they are, rodents are elusive animals. You'll have more luck sighting a deer or coyote than the quick and alert mouse. They are brown or gray and match their environment. Small animals which have no means of active defense frequently depend upon concealment alone for safety. In addition, many rodents are burrowers, and their underground lifestyle makes them difficult to observe. Many rodents sleep through the hottest part of the summer and much of the winter, so are not above ground when you might look for them. If you have rodents in your home, you may see them more often than when you are hiking or wildlife-watching; you will certainly see unwelcome evidences of their presence in your drawers and on your floors.

However, look for indications of rodents in the wild, and you will find it. If you see mounds of dirt that are heart- or horseshoe-shaped, you've found the soil from a pocket gopher tunnel. These hard workers can move approximately a ton of soil to the surface each year. This enormous achievement reflects the gopher's important ecological function. Their old tunnels contain vegetation and droppings and become deep fertilization for the soil. They also cause the soil to become mellow and porous. Many mammals, large birds and snakes eat gophers and depend on their burrows for homes. Salamanders, toads, and other creatures seeking cool, moist conditions take refuge in unoccupied gopher burrows. Lizards use abandoned gopher burrows for quick escape cover.

If you find a uniform-shaped soil mound that appears similar to a little volcano, a rodent didn't do it! Who did? A mole pushed the loose soil from his newly-built tunnel onto the ground surface. What—isn't a mole a rodent? No, moles are mostly carnivorous, preferring yummy insect grubs, adult insects and earthworms. Therefore, moles are not rodents, "gnawers," but soricomorphs, meaning "shrew-shaped." Now you can quit blaming moles for eating your gladiola bulbs.

Voles, small field mice, don't make mounds. Instead, they construct two-inch wide, well-defined, visible runways at or near the surface. Vole runways result from the voles eating the grass blades, as well as from the constant traffic of numerous little feet over the same path. During winter, the plump little vole abandons his underground nests and tunnel system and builds new ones beneath the snow. When the snow melts, the vole again moves below ground, leaving evidences of his winter tunnels and abode behind.

More signs of rodents are small, parallel teeth marks where rodents acquired nutrition in a tree's bark or cambium. Voles do not climb trees, so look for tiny teeth marks near ground level. Porcupines make 1/4-inch-wide teeth marks at an angle to the tree, often in the tops of trees as they sit in the branches. Their teeth marks are often parallel to the branch.

Rodent tracks in dust are common in dry environments. Look for them approaching burrow entrances or in trails. Holes in the sides of seed or nut shells show that a rodent had a good meal. Look for small, dark feces, or scat. That is a sure sign that a little rodent being has passed by.

So, the next time you see a mouse, we hope you appreciate the variety and complexity of his family.