May 2, 2022
Eastern woodrat, Neotoma floridana. Photo by Sturgis McKeever, Georgia Southern University,

Eastern Woodrats Have Returned to the Shawnee National Forest

By Tiffanie Atherton, Ed Heist, Clayton K. Nielsen
A small gray, tan rodent with white under its chin in a metal cage.
Photo by Stan McTaggart, IDNR.

Packrat. Trade rat. Woodrat. All three are common names for a unique group of small mammals known for their peculiar habit of collecting. The woodrat genus, Neotoma, consists of 22 distinct species inhabiting woodlands across much of the United States and Mexico. Fur colors range from light grey to red-brown backs and white to red-brown bellies. White feet, large eyes, large ears, and a furred tail make the woodrat an adorable small mammal with even the largest of the species weighing less than 1.5 pounds. 

Woodrats are vegetarians, feeding on nuts, seeds and other plant matter. In a woodland habitat they are known to build large ‘middens,’ or mounds out of sticks, leaves, and various vegetation. Multiple tunnel-like extensions off the middens allow for ample safety while foraging at night. Unlike nuisance rat species that nest in colonies, woodrats are solitary dwellers. They are fiercely territorial and will defend their middens; thus, it is unlikely that multiple woodrats would nest together. Additionally, their large middens may act as refugia for raccoons, opossums, foxes, snakes and other small animals. 

A gray, brown rat climbing a sandstone boulder covered in green and gray lichen.
Photo by Stan McTaggart, IDNR.

In locations where caves are present, the caching (collecting and storage behavior) by woodrats adds organic matter into the otherwise nutrient-deprived habitat. In southern Illinois, it is believed that woodrats utilize sandstone and limestone bluff systems to avoid predation and unfavorable environmental conditions, such as harsh winter weather, potentially minimizing local extinction events. Instead of a large ground midden, in bluffs, woodrats block the entrances to their middens with sticks and leaf matter. Studies suggest woodrats may act as an indicator species of forest habitat health and are a primary food source for predators, particularly nocturnal predators, such as raccoons, hawks, snakes, owls and foxes. Their collecting habits may also be important in archeological studies as middens are often recycled and expanded upon, resulting in generations worth of ‘historical loot.’

Of the 22 woodrat species, four are endangered or possibly extinct and many additional populations are declining. Illinois’ local woodrat species, the eastern woodrat, Neotoma floridana, was on the Illinois State Endangered Species List from 1997 to 2020. Prior to the establishment of the Shawnee National Forest in 1933, timber harvest had removed much of the forested landscape resulting in disconnected habitat patches and minimal canopy cover. By the late 1900s, the species was thought to exist in only a few small, isolated populations in the far western portion of the forest at LaRue-Pine Hills, Fountain Bluff, and Horseshoe Bluff. Seeing a need for action, the Illinois Department of Natural Resources (IDNR) drafted a Species Management Plan to aid in eastern woodrat recovery.

A graphic including the southern portion of the state of Illinois by counties. The map shows where wood rats were reintroduced and where remnant populations are located.

Two different management actions were utilized in eastern woodrat recovery. The first action consisted of an augmentation in the western portion of the Shawnee National Forest, where small remnant populations continued to persist at LaRue-Pine Hills and Fountain Bluff. An augmentation occurs when new, unrelated individuals (in this case, eastern woodrats from Missouri and Arkansas) are added to an existing population. As wildlife populations decrease in size, the risk of inbreeding, or mating between relatives, increases. The addition of these artificial migrants may reduce negative effects associated with inbreeding, such as reduced offspring viability. Funded via the Federal Aid in Wildlife Restoration Program distributed by the IDNR, short-term follow-up studies conducted by Southern Illinois University Carbondale reported increased capture success following the augmentation, indicating an increase in census population size. 

The second management action was a reintroduction of eastern woodrats in the eastern portion of the Shawnee National Forest, with a goal to reestablish populations. From 2003 to 2009, 427 eastern woodrats were collected from LaRue-Pine Hills (64 eastern woodrats), multiple locations in southern Missouri (166 eastern woodrats) and northeastern Arkansas (197 eastern woodrats). Eastern woodrats were released at five locations containing suitable habitat for woodrats in the eastern portion of the Shawnee National Forest. Reintroduction locations included Garden of the Gods, Buzzard’s Point, High Knob, Pounds Hollow and Lusk Creek. These reintroductions were conducted over multiple years with relatively few individuals (less than 30) being released at a time. Although woodrat recovery efforts in other states had been unsuccessful, our field studies conducted from 2011 to 2014 indicated species recovery efforts had been successful as evidenced by recent reproduction and high capture numbers of wild-born woodrats. 

A biologist in a blue shirt wearing a blue bandana holds a gray rat while conducting research. In the background is a lush green woodland.
Eastern woodrat handled by Seanessy Lyons (2019 field and lab technician). Photo courtesy of Tiffanie Atherton.

As woodrat populations across the United States continue to decline, it is important that wildlife managers understand why reintroduction and/or augmentation efforts in southern Illinois were successful. Given researchers collected tissue samples from all relocated woodrats and woodrats were collected over multiple field seasons post-augmentation, our research team at the Cooperative Wildlife Research Laboratory and Conservation Genomics Laboratory at Southern Illinois University Carbondale is currently determining whether reintroduced eastern woodrats are interbreeding between source populations and how these reestablished and augmented populations have changed since the implementation of management actions. Long-term genetic monitoring of eastern woodrat populations will allow wildlife managers to determine whether eastern woodrats warrant continued management or if the implemented management actions have resulted in self-sustaining populations that no longer require management. Migration among populations is vitally important for the long-term persistence of fragmented wildlife populations, allowing for the maintenance of genetic variation. Genetic analyses will provide wildlife managers with answers to important questions such as: Has inbreeding decreased in the western Shawnee National Forest since the augmentation? Are woodrats migrating between reintroduced populations in the eastern Shawnee National Forest? Are habitat alterations, such as migration corridors between habitat patches, a viable or necessary modification needed to aid in eastern woodrat persistence?

Two biologists carry packs of metal traps on their backs along with research equipment and bottles of water. In the background is lush green shrubby vegetation.
Tiffanie Atherton (PhD student and eastern woodrat researcher) and Ari Szubryt (2020 field and lab technician). Photo courtesy of Tiffanie Atherton.

Initial results indicate eastern woodrat populations continue to persist in the Shawnee National Forest and that populations are spreading, with eastern woodrats captured over 9 km (5.6 miles) from release sites. Surveys we conducted from 2012 to 2014 reported 63 percent of captured females showed signs of reproduction. With an increase of migrants exiting current populations, there may be hope for the establishment of a metapopulation, or a collection of populations that evolve independently, while still exchanging some genetic material through migrants. While woodrat recovery has been difficult for many woodrat species, such as the Allegany woodrat and Key Largo woodrat, initial results suggest that Illinois’ eastern woodrat recovery was a success!

Tiffanie Atherton is a PhD candidate at Southern Illinois University where she studies eastern woodrat genetics through the Conservation Genomics Laboratory and the Cooperative Wildlife Research Laboratory under Dr. Ed Heist and Dr. Clay Nielsen. She obtained her Bachelor’s degree in Wildlife and Conservation Biology and Master’s of Natural Science at Southeast Missouri State University.

Dr. Clay Nielsen is Professor of Wildlife Ecology and Conservation at the Cooperative Wildlife Research Laboratory at Southern Illinois University.  

Dr. Ed Heist is a Professor of Zoology and Associate Director of the Center for Fisheries, Aquaculture and Aquatic Sciences at Southern Illinois University. He earned his Ph.D. from the College of William and Mary. Dr Heist is a conservation geneticist who runs the conservation genomics laboratory at SIUC and also teaches classes in genetics and marine biology.