Thursday, August 11, 2011

Thirteen-lined ground squirrels (not chipmunks, not gophers)

Thirteen-lined ground squirrels (not chipmunks, not gophers)

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My encounters with ground squirrels in the west this summer reminded there’s a common, yet fascinating animal closer to home I’ve been meaning to profile, the thirteen-lined ground squirrel. Do you know the one I mean?

If you’ve had a small squirrel dash in front of you as you drove on a country road bordered by crops, or you’ve seen a chipmunk-looking critter darting about in a cemetery, you’ve probably encountered a thirteen-lined ground squirrel. Some people call thirteen-liners gophers because they live in the ground, but in scientific terms, they’re members of the squirrel family.

Thirteen-lined ground squirrels are among those animals that have benefited from human development because they thrive in the close-cropped landscapes we create, from roadsides and pastures, to cemeteries, golf courses, parks and other lawns. Their geographic range, which encompasses much of the central U.S. and Canada, has actually expanded over the past two centuries.

If you were to draw a thirteen-lined ground squirrel based on its name, you would produce a picture that left out a notable characteristic of the original. Yes, they are marked by about thirteen alternating stripes of dark brown and light tan fur that run from neck to tail. But what’s equally striking is that the wider, dark lines are decorated along their entire length with evenly spaced light dots, giving them a star-spangled appearance. There’s a golden tinge to some of the lighter fur on thirteen-liners, and they’re the creature on which the University of Minnesota’s Golden Gopher mascot is based.

Thirteen-lined ground squirrels eat just about anything they can get their little paws on, from insects of all sorts to the occasional small vertebrate (including carrion), to grasses, flowers, seeds and crops. They have pouches in their cheeks that they use to transport food to their burrows for eating later. (If you have trouble with thirteen-lined ground squirrels eating from your garden, University of Illinois Extension’s “Living with Wildlife” Website provides suggestions for dealing with them:

Thirteen-lined ground squirrels are, in turn, food for a wide range of other animals, including coyotes, foxes, weasels, dogs, cats, hawks, owls and snakes.

One way thirteen-liners avoid being eaten is by excavating short, shallow escape burrows throughout their territories, so they’re never far from a hole to dive into. They also create deeper, longer burrows for nesting and hibernating.

And thirteen-lined ground squirrels hibernate like champions. After fattening up in the Fall, they retreat to a chamber that’s below the frost line, plug the entrance with soil, and curl up for about four months. During hibernation—which begins in late October or early November and lasts until late March or April—their body temperature nearly matches the temperature of the burrow, dropping as low as 37 degrees F. By the time thirteen-liners awaken, they have lost up to half of their body mass.

During the months thirteen-lined ground squirrels are active, you need not get up early to see them, nor do you need to brave inclement weather. They are most active on warm, sunny days, and they don’t even bother coming out of their burrows in the rain.

To learn more about thirteen-lined ground squirrels, or any of the other mammals you might see when you’re out and about in the Prairie State, let me refer you to the source for much of the information in today’s commentary, the Field Manual of Illinois Mammals by Joyce E. Hofmann. It’s published by and available through the Illinois Natural History Survey, which is a division of the Prairie Research Institute at the U of I in Champaign.