The year of the chipmunk invasion

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I don’t know if it’s just me, but chipmunks are tough to ignore this year. Every day they dart on and off the bird feeders, and when I drive the two miles out to the main road, I see at least a dozen dashing back and forth across the road. I haven’t hit one yet, but I suspect I eventually will.

Common in the backyard

Chipmunks are among the most familiar backyard wildlife. With a body about six inches long and a four-inch tail, chipmunks are small, striped ground squirrels. They weigh about four ounces. Five dark stripes run the length of the body with the longest running down the center along the spine. The two dark stripes on each side are separated by a prominent cream-colored stripe.

Predators

Of course, I know the abundance of chipmunks won’t last. Too many hawks, black rat snakes, and weasels feast on them when their numbers explode. By the end of summer, the chipmunk population will return to normal. If any rodent can sustain heavy predation, it’s the eastern chipmunk. Throughout much of its range, chipmunks raise two broods each year. After a gestation period of about 31 days, four or five young are born in early April or May.

At birth, the pups weigh about 0.1 oz. and are naked and blind. At one week of age, their stripes begin to show, and after a month they weigh about an ounce, their eyes open, and they are covered in fur. Weaning occurs at about six weeks of age when they weigh about 1.4 oz. A second brood arrives in August.

Chipmunks and birds

The flurry of activity I’m seeing right now is no doubt due to a very successful first brood. This could be trouble for birds that nest close to the ground, such as song sparrows and field sparrows. Chipmunks are carnivorous this time of year, and bird eggs and nestlings are a favorite food. In field studies of nesting success of ground-nesting birds, chipmunks are among the most significant predators.

Because chipmunks are favorite prey of so many predators, they are constantly alert. I call them “pathologically alert,” because if they let down their guard for even a moment, they may fall victim to a predator. So it’s zig here, zag there. Only in their burrows can they truly relax. Until a tiny least weasel comes snaking through the tunnel. Though it weighs less than a chipmunk, a hungry least weasel makes its living skulking through burrow systems of other small mammals.

Safe haven

Usually, however, the burrow is a safe haven for chipmunks. The main entrance is usually hidden under a rock, a stump, or a log. It plunges straight down for several inches, then levels off for 20 feet or more. Along the way, it may branch several times with each branch leading to additional entrances.

Inside the burrow system, chipmunks excavate several larger chambers, which can be as much as three feet below the surface of the ground. One is used as a nest to sleep in, another as a food storage area, and another as a latrine. Females give birth to their pups in the nesting chamber. The food storage chamber can be large enough to store as much as a half-bushel of nuts and seeds. On hot summer days, chipmunks may escape the heat by staying underground.

Solitary lives

Except when females raise their young, chipmunks lead solitary lives. They are extremely territorial and antisocial. Each individual occupies and defends its burrow system. Aggressive displays include chases and a variety of vocal chips, trills and “cuks.” In fact, chipmunks are often heard before they are seen. At times they vocalize almost constantly to insure that nearby chippies know that intruders will not be tolerated.

No hibernation

During cold weather, chipmunks do not truly hibernate. They forego accumulating heavy layers of fat to get them through long periods of deep sleep. Instead they wake periodically and eat the nuts and seeds stored in their larders.

If you’re plagued by an overabundance of chipmunks this summer, you’re not alone. But take comfort in the adage that, “This too shall pass.”

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Scott Shalaway, who holds a Ph.D. in wildlife ecology from Michigan State University, writes from his home in rural West Virginia. A former faculty member at Oklahoma State University and the University of Oklahoma Biological Station, he has been writing a weekly nature column for newspapers and freelancing for magazines since 1986. He can be heard on Birds & Nature from 3-4 p.m. Sunday afternoons on 620 KHB Radio, Pittsburgh, or live online anywhere at www.khbradio.com, or on the Tune-In radio app. Visit his website at www.drshalaway.com or contact him directly at sshalaway@aol.com or 2222 Fish Ridge Road, Cameron, WV 26033.

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