Fieldbook of Illinois Mammals

1. What they did

This is a pocket field guide to the wild mammals of Illinois, written for hikers, naturalists, students, hunters and interested laypeople. It was begun by Carl Mohr of the Illinois Natural History Survey over a decade before publication and completed by Donald Hoffmeister, Curator of the University of Illinois Natural History Museum, with Mohr.

The book has five main parts:

• Where mammals live. Habitats and how each species’ range is set by habitat and climate.
• How to study mammals. Watching live animals, directly or through their signs, and making a collection of preserved specimens.
• Signs. A chapter on reading homes, trails and runways, tracks, scats, tooth marks and food signs, with a key to tracks and plates of tracks, track patterns and droppings.
• Synopsis of Illinois mammals. Identification keys and an account of each species, with description, life history, signs and distribution.
• Prehistoric mammals and the future. Ice Age mammals once found in Illinois, and a closing chapter on habitat loss.

2. What they found

Mammals in Illinois

• Besides people and domestic animals, 59 species of wild mammals were known in Illinois. Mice, shrews, rabbits and squirrels were the commonest.
• Mammals are numerous on almost every acre of uncultivated land, probably 5 to 12 times as numerous as birds. Woods may hold 10 to 60 mammals per acre, and about 95% of them are chipmunk size or smaller.
• Most are active at night or live in burrows, so hikers rarely see them.
• Bison, elk, bears, wolves, mountain lions and some others had vanished from the state. By 1814 the bison had gone, leaving their well-trodden paths. The red squirrel was the most recently lost species.

Reading signs

• The authors call sign reading “a type of detective work”: a process of elimination using the kind, size and form of the sign, which species occur in the area, the habitat and the season. Their worked example narrows small tracks in snow in southern Illinois to a fox squirrel or a muskrat, and a tail mark points to the muskrat.
• Often signs narrow the list to a few species but not to one. A combination of signs (home and tracks, or runways and food remains) gives a good chance of identifying the species.
• Homes: burrows are sorted by entrance size (under 2 inches for mice, voles and shrews; 2 to 4 inches for ground squirrels, gophers, chipmunks, moles and rats; over 4 inches for woodchucks, badgers, skunks, opossums, raccoons, otters and coyotes). A mole mound is steep and conical with raised runs; a pocket gopher mound is a rough crescent with no visible runs. Mammal nests are almost always roofed over, unlike most bird nests, and the only sure way to know who lives in one is to see the occupant.
• Trails: high trails (open paths of larger animals such as foxes, rabbits, woodchucks and coyotes), runways (low tunnels of shrews, voles and mice) and slides (otters, minks and muskrats).
• Tracks: among the most reliable signs. Running animals leave prints farther apart than walking ones, often in a different pattern, and prints in thick mud spread wider than in thin mud. A key sorts tracks by hoof or toe marks, number of toes, claw marks and webbing.
• Scats: carnivore and opossum scats are cylindrical with hair, feathers, bone and insect parts; herbivores leave small pellets. Where scats are left can matter: swamp rabbit droppings look like cottontail droppings but are left on logs and mounds.
• Tooth marks and food signs: for example, moth and fly wings indicate bats; turtle egg fragments around a shallow hole indicate a skunk or raccoon; bundles of cut grass 2 to 3 inches long indicate a jumping mouse; and felled trees, cut twigs and wide tooth marks in bark “can mean only the work of a beaver.”

Species accounts

Each account gives size, colour and skull details, life history, signs and distribution. The red fox account, for example, gives print size (front about 2 inches long), a slender ball pad print that tells red from gray fox in fine mud or wet snow, prints in a nearly straight line when walking or trotting, strides of 14 to 16 inches indicating a trot, scat length, den features, and rabbit skulls left with the nasal and basal parts gnawed off.

3. What they concluded

• Most species present at settlement were still in Illinois, but many survived despite, not because of, people. Agriculture has narrowed or removed habitat, and many species are now confined to a few small patches.
• When a species becomes rare or disappears, it signals the loss of the natural conditions that supported it, as the bison’s loss signalled the loss of extensive prairie.
• Heavy grazing of pastures and woodlands, erosion, water pollution and careless use of herbicides and insecticides were reducing wildlife. In 1949, two thirds of privately owned Illinois woodland was being pastured.
• Parks, forest preserves, a national forest and roadside and railroad verges were helping. Beavers and white-tailed deer had been restored, and most furbearers were more numerous than 25 years earlier. “We can have more productive land and more wildlife. But there still is a long way to go.”

4. How tracking was or was not used

This is a guide, not a field study, so no tracking was carried out for it. Tracks and signs identification is one of its main subjects: a whole chapter on signs, a key to tracks, plates of prints, track patterns at different gaits, droppings, food fragments and tooth marks, and a signs section in each species account. The authors write that the most observant hunters, trappers and naturalists are usually highly skilled at reading signs, and that a hiker can train themselves to do the same.

6. Other technologies, skills or innovations

• Two-part identification keys: one using external features, and one using only the skull and teeth, for skulls found in the field, in stomach contents or in owl pellets.
• Four ways to preserve tracks: photographs, sketches, plaster of Paris casts, and candle tallow dripped into tracks in mud.
• Field methods for studying small mammals: marking a plot into squares (quadrats) and mapping runways, nests and feeding stations on graph paper; baits and squeaking calls; following animals at night by flashlight.
• Instructions for collecting, measuring and preparing study skins and skulls.

7. Implications for conservation (from the paper)

• Simple changes can raise the number of mammals an area supports: nest boxes in woodlots with few hollow trees, multiflora rose fences, ungrazed ditch banks, and leaving brush and rotting logs in woodlots.
• Managed, unpastured woodland is better for wildlife and for timber than pastured woodland.
• Amateur collectors can add to knowledge of where species occur, if they collect, preserve and label carefully.