CHAMPAIGN, Ill., 6/13/22: Eastern woodrats in southern Illinois scurry along the forest floor at night, collecting seeds from hardwood trees, mushrooms, and other debris to bring back to their nests made of sticks in the rock outcropping crevices. Their population was once in peril in the state, but Illinois State Biologist Eric Schauber reports that reestablished populations have successfully recovered, likely because of the abundant nest sites in the forest.
The population had dwindled to a few dozen woodrats along the Mississippi River bluffs in the early 2000s, according to Schauber, also the Illinois Natural History Survey director. To reverse that decline, the Illinois Department of Natural Resources (IDNR) relocated 363 eastern woodrats from Missouri and Arkansas to several sites in southern Illinois from 2003 to 2009.
In a new study published in the Journal of Mammalogy, Schauber and Aaron Gooley, a doctoral graduate of Southern Illinois University Carbondale, analyzed capture histories of 205 woodrats in the summers of 2013 and 2014 in areas of the Shawnee National Forest where woodrats had been reintroduced. The goal was to estimate local population size and determine how abundance and survival rates were associated with availability of nest-site crevices in rocks, the abundance of owls as predators, availability of nut-producing trees, and the risk of raccoon roundworm infection, which is fatal to woodrats.
“Our role was to answer the question of why woodrat populations declined in the first place and what explains why they may be more successful in some places, but not in others,” Schauber said.
Woodrats in southern Illinois build their stick dens in sandstone rock crevices, where these “packrats” store food and other items. After one woodrat dies, another moves into the same den, adding new layers of debris. This succession can carry on for decades, and archaeologists have even studied woodrats’ dens to examine the objects cached there.
The woodrats’ packrat tendencies leave them vulnerable to worms found in raccoon feces, which become more infectious as the feces dry. Although raccoon roundworm is a common cause of woodrat population declines, the data showed no signs of the parasite in the Illinois study sites.
The researchers also found that the owl population abundance was not a factor inhibiting woodrat recovery, and that food from oaks, hickories, and other trees was plentiful. Instead, the availability of good den sites had the strongest impact on how many woodrats live in an area.
“This study helps us predict places where woodrat reintroductions are going to be the most successful,” Schauber said. “Findings also suggest that paying close attention to the local trees and how many owls are present is not going to be the most informative in future studies and for conservation. The general availability of forest habitat with outcrops and crevices is probably a good indicator of where woodrats will thrive.”
Findings of previous studies by Gooley and Schauber documenting the woodrat’s recovery led to the eastern woodrat being removed from the Illinois Endangered Species List in 2020.
“They are a part of the Illinois biodiversity that was almost gone,” Schauber said.
The latest study was funded by the IDNR, U.S. Fish and Wildlife Service, and the SIUC Department of Zoology.
Media contacts: Eric Schauber, 217-300-7827, firstname.lastname@example.org