By Jim Pease
Iowa State University Extension
If they are small, brown, furry and crawl on the ground, most people tend to lump these mammal species under "gopher" or some other all-encompassing name. Different species have different requirements for food and shelter. Understanding those differences can help you manage their populations.
The 13-lined ground squirrels are those six-inch long (plus about three to four inches of tail) critters of open grassland areas. Once uncommon in Iowa, they are now abundant across the state as we have created "short-grass prairie" areas in the form of mowed lawns, pastures, golf courses and cemeteries. They like the changes we've brought to the landscape. They hibernate for about five winter months, emerging in March to early April. They burrow in the ground in open, short-grass areas, leaving little visible dirt and holes the size of 50-cent pieces.
The eastern chipmunk is the same size as the ground squirrel, but is found in more woodland or woodland edge habitat and has only two light stripes. Absent only from the northwest corner of Iowa, they inhabit neighborhoods with mature trees and shrubs, rock and wood piles and retaining walls. While they may live in holes dug in the ground, they are more likely to live in the retaining walls, beneath decks or even in holes in trees. They do not hibernate in the winter and, though they sleep for days at a time, can be seen raiding bird feeders on warm winter days.
Ground hogs, also known as woodchucks or whistle pigs
The ground hog is really a large ground squirrel. Like the 13-lined, it hibernates through the winter, living in torpor (with body temperatures below 40 F) below the frost line. Adults can range from 24-30 inches long plus a three- to four-inch furry tail and weigh from 9-14 pounds. They inhabit a wide range of habitat, from woodland (yes, they can climb trees) to grassland. Most typically, they live in holes in the ground, often below decks and outbuildings. Their holes are round and vary from 7-10 inches in diameter. Mounds of dirt outside the main entrance are often large and obvious. Like ground squirrel and chipmunk dens, however, there are usually other, more hidden entrances.
All three of these species have diets of plants (grasses, leaves, seeds, nuts, berries, fruits, bulbs) though they are known to occasionally supplement their diet with animal protein (ground nesting birds, eggs). All are ecologically important and interesting to watch, but can be nuisances depending on location. Reduce summer bird feeding of large seeds (sunflower, safflower, peanuts) to reduce attracting these mammals.
Trapping better than poisoning
Live traps baited with peanuts (or fresh-cut apples for ground hogs) and subsequent release at least five miles distance can be successful. Rat-sized snap traps baited with peanut butter (can be covered with boxes with the ends cut out to be sure birds don't get caught) and placed outside main entrance holes can quickly reduce a local population.
Poisons that contain zinc phosphide as the active ingredient are available, but must be carefully used to avoid non-target species. Poisonous gas cartridges may be appropriate for some limited circumstances, but kill everything in the burrow, including toads, turtles and other species that may be co-habitating with the digging mammal. For this reason, trapping is preferred over poisoning.
James Pease, Natural Resources Ecology and Management, (515) 294-7429, firstname.lastname@example.org
Lynette Spicer, Extension Communications and External Relations, (515) 294-1327, email@example.com