Winter 2002

Franklin’s Ground Squirrel: vanishing prairie hibernator

Photo: Joe Nowak

Let’s travel back in time 200 years to a warm spring day in early May. We’re Potawatomi native

Americans walking along the Des Plaines River, near where Chicago Avenue in River Forest is now. Tallgrass prairie, sometimes interspersed with oak savanna and wetlands, stretches as far as the eye can see. Passing our tribe’s Snake Effigy Mound, we notice 3- to 4-inch holes dug into the side of the mound that were not there last spring. We turn and walk in the prairie. Suddenly we hear rapid trilling whistles, unlike those of any bird. Absolutely still, we try to pinpoint the sound. Our reward is the sight of several ground squirrels peeking out over the intermediate grasses near the river. Unlike common 13-lined ground squirrels, these animals are much bigger (14-16 inches long), and have greyish-brown bodies without stripes. We hear more distinctive whistles, and our new friends seem to vanish. Looking more closely we find more 3- to 4-inch holes with small mounds in front of them. Altogether we find about 10 burrows, though we see no additional ground squirrels. We have found a Franklin’s ground squirrel colony.

Franklin’s ground squirrel (Spermophilus franklinii) is a local, little-known prairie mammal. Their distinctive call causes them to be known as whistle pigs. Sometimes they are also called grey gophers. In Illinois, Franklin’s ground squirrels prefer habitats with intermediate and tall grasses. They are not found in areas with short or mowed grasses. Though Franklin’s ground squirrels are diurnal, they are less often seen than heard. A Franklin’s ground squirrel burrow must be deep and well drained to be insulated from heat and cold. In 1855, Robert Kennicott wrote that Franklin’s ground squirrels dug burrows in river and ditch banks. Today the beds of elevated railroad rights-of-way seem to provide similar, acceptable habitats.

One of the true hibernators, it sleeps from about September to April with a body temperature just a few degrees over freezing. Right after coming out of hibernation, it breeds and has a single yearly litter of 6-9 pups around early June. Probably the least herbivorous ground squirrels, Franklin’s ground squirrels eat insects, green plants, seeds, fruit, amphibians, bird eggs, young birds and mammals, and carrion. Their principal predators are the red-tailed hawk, red fox, badger, coyote, striped skunk, mink, and long-tailed weasel. Their home range is usually 1.5-3 acres. At adolescence, male juveniles disperse for an unknown distance. In the wild, life expectancy is 4-5 years for females and 1-2 years for males.

Since more than 99 percent of prairie has been lost since European settlement, prairie mammals, including the prairie deer mouse, prairie vole, and Franklin’s ground squirrels have suffered. Con-sidered by some an agricultural pest, the Franklin’s ground squirrel has been systematically exterminated. In the late 1800s, millions of these squirrels were killed for bounties of up to 10 cents per skin. Similar attitudes persist today, despite little evidence that Franklin’s ground squirrels cause much crop damage (which is not very surprising, given their omnivorous nature). Indeed, there is good evidence that they avoid row crops, and are only occasionally found in cover crops. Franklin’s ground squirrels do sometimes eat game bird eggs and, as a result, are not well liked by some bird hunters.

Today the Franklin’s ground squirrel is very rare in the Chicago Wilderness region, as well as in the United States in general. Its historical range is the north central United States, including the northern two-thirds of Illinois, and south-central Canada. The Franklin’s ground squirrel is listed as endangered in Indiana, imperiled in Wisconsin, and rare in Iowa. It is not listed in Illinois. Oliver Pergams and Dennis Nyberg wrote a Franklin’s ground squirrel Species Action Plan for the World Conservation Union, and gave the Franklin’s ground squirrel a global rating of “Vulnerable” in the next International Union of Conservation Scientists’ Red List. They found that the Franklin’s ground squirrel is declining greatly throughout most of its range.

Given the extent of prairie loss, it is not surprising that the Franklin’s ground squirrel is rare. But there are substantially fewer populations of them than there were even 10 years ago. The continuing loss is mysterious. While additional prairie was lost in the last 10 years, it is probable that more acres were restored than lost recently, and there have been attempts to reintroduce the Franklin’s ground squirrel to suitable habitat. For instance, Ron Panzer’s reintroduction of Franklin’s ground squirrels to Gensburg-Markham Prairie in 1983-84 was successful through at least 1987. However, much of the remaining prairie persists in small patches, such as railroad rights-of-way and pioneer cemeteries. Most remaining prairie patches may be too small to support a large enough population to be viable, or perhaps the continuing invasion of prairie by woody vegetation is the cause of loss.

More information can be found at:http://www.fgs.info

—Alex Pergams and Oliver Pergams