The squirrel that loves to sleep

StoryImage( ‘/Images/Story//img-1helDac2ND.jpg’, ‘Photo by Dr. Robert Hedeen’, ‘A 13-lined ground squirrel surveys the landscape from his burrow in the Byron Forest Preserve.’);

Every country boy in middle North America is familiar with the 13-lined ground squirrel (Spermophilus tridecemlineatus). This rodent is sometimes called a gopher, but biologists usually reserve that name for another species. The ground squirrel is yellowish-brown in color and has 13 longitudinal stripes down its back and sides, some of them dotted with rows of yellow spots. Occasional albino and melanistic (dark) specimens are seen. His body is small and slender, about 11 inches in length including a 5- to 6-inch tail, and his cheek pouches for storing seeds are rather large.

These squirrels dig burrows that are 15 to 20 feet long and may have more than one entrance. The entrance is inconspicuous, appearing only as small, 2-inch diameter holes in the ground. Mounds of dirt resulting from the excavations are never allowed to accumulate, but occasionally the grass around the entrance may appear to be well worn. The burrow entrance is plugged from the inside at night. These squirrels are usually solitary, though they sometimes may congregate in loosely structured communities.

The 13-lined ground squirrel apparently loves its sleep as the average hibernation period throughout its range is about 250 days, from fall to spring, and this extended period of snoozing is unique. This long period of hibernation is probably correlated with the early disappearance of green vegetation, which is its main food item. Green vegetation in some regions of Illinois is usually present throughout the summer and fall in contrast with drier areas, so perhaps, in this state the period of hibernation is shorter.

Populations of these ground squirrels vary greatly from situation to situation and the time of the year. They live in short grasslands or in weedy areas where the weeds are not too tall. This is because they have many enemies, and when they sit upright at the entrance to their burrows, they must be able to see in all directions. Consequently, grassy areas that are well cut, such as golf courses, cemeteries, and roadsides are ideal habitats. Woods and marsh areas are avoided. The draining of marshy areas in central Illinois by early settlers surely made more land available for the squirrels to inhabit

In Illinois, the 13-lined ground squirrel is mainly found in the northern and central parts of the state, north of a line reaching from Madison County in the west to Clark County in the east. This unusual distribution probably is because the area of the state south of this line generally corresponds with the Shelbyville glacial moraine. Below this moraine, the soil is thin with an underlying hardpan, and this prevents the squirrels from digging adequate burrows. If the burrow is too shallow, the animals may freeze during a long, cold winter.

As a boy in north Texas, I spent many a pleasant afternoon (for me) snaring ground squirrels. A noose on the end of a string was placed around the inside of a burrow just below the top, and I waited a few yards away at the end of the string. A ground squirrel usually appeared a short time later, poking his head out to see if the coast was clear. A pull on the string was all that was required to catch the varmint. After an unsuccessful attempt to tame a noosed ground squirrel as a pet, I released unharmed all of the animals I caught.

Thirteen-lined ground squirrels can cause problems when they burrow into lawns, golf courses, cemeteries, and parks. They also can make a nuisance of themselves by digging up newly planted seed, consuming sprouting seeds, and damaging garden vegetables. The generic name of the squirrel, Spermophilus, means seed loving in Latin.

In certain areas of the Southwest, ground squirrels may present a medical problem for humans. They, along with prairie dogs and some other rodents, may become infected with sylvatic plague, the disease in animals that is the same as bubonic or urban plague in man. Humans may become infected with plague bacteria if they come in contact with diseased animal tissue or the vector fleas.

Some years ago, this writer supervised a survey team that was charged with determining if there was any danger from sylvatic plague to the thousands of troops scheduled to participate in a joint Army-Air Force maneuver on the vast reservation of Fort Hood, Texas. Of the several hundred ground squirrels we captured and tested, only two were found to be positive for plague.

One can be sure that my crew and I were eager to have the immunization for plague administered before we went into the field and were careful to wear gloves when handling an animal for examination.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

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