Bruce Nathanson asked a question that made me scamper around to dig up an answer.
“I live in the northern suburbs—I have never seen more rabbits,” he emailed. “The good news is that there are no chipmunks this year. Normally we are overrun with chipmunks. Please ask your experts what happened to the chipmunks.”
Illinois State Biologist Eric Schauber suggested I reach out to Robert Schooley, head of the Department of Natural Resources and Environmental Sciences at the University of Illinois.
I broadened Nathanson’s question out to be chipmunks and ground squirrels. Ground squirrels caught my eye last spring during the lockdown period for the pandemic when I saw a 13-lined ground squirrel flitting between our flower and vegetable pots on our small back patio.
First some refining of the definitions seemed important.
“Strictly speaking, we just have Franklin’s ground squirrels and thirteen-lined ground squirrels,” Schooley emailed. “More broadly, if you group `ground squirrels’ versus `tree squirrels,’ then the ground squirrels include eastern chipmunks and woodchucks.”
I was surprised to find woodchucks (groundhogs) lumped with chipmunks. Growing up, I assumed groundhogs were related to bears because they look similar. By the way, Illinois has four species of tree squirrels: fox, eastern gray, red and southern flying.
As to how our two ground squirrels are doing, Schooley broke it down like this, “Franklin’s ground squirrel is state listed as a Threatened species in Illinois. They are also an Endangered species in Indiana and a Species of Concern in other Midwest states. They have suffered from the tremendous loss and fragmentation of tallgrass prairies and now occur in small patches of grasslands including along roadsides and railroads. However, research by a former PhD student of mine, Dr. Jenny Duggan, showed that Franklin’s in Illinois were not necessarily a prairie obligate species. For instance, they also occur in smooth brome grasslands but only if they are not mowed regularly.
“Thirteen-lined ground squirrels seem to be doing fine. Unlike Franklin’s, they inhabit mowed areas including roadsides, lawns, parks, and such.”
So the 13-lined ground squirrel I had spotted last spring was not that unusual.
As to chipmunks, Schooley emailed, “I am not aware of any recent monitoring of chipmunks in Illinois. But in general, they occur throughout most of the state and are not a species of concern.”
Nathanson’s question made me wonder if there was a natural cycle of ups and downs in populations. I was thinking of the nine- or 10-year population cycles of ruffed grouse.
But Schooley emailed, “To my knowledge, grounds squirrels and chipmunks do not have regular population fluctuations (aka population cycles) like voles do in some regions where they might irrupt every four years. But abundances of ground squirrels and chipmunks can vary a lot from year-to-year, probably due to weather affecting their food resources.”
Because it helps people to take conservation seriously, I asked what role they play in the ecosystem.
“Chipmunks and ground squirrels are prey for many predators, so they are an important part of food webs,” Schooley explained. “Their burrows provide microhabitat for other species of vertebrates and invertebrates. Also, their burrowing activity can help with soil aeration and water infiltration.”
Many of our lesser known animals seem to be impacted by the modern world in an unfavorable way, so I asked if any ground squirrels disappeared in the last couple hundred years?
“I do not think so in the United States,” Schooley emailed. “There currently is one federally endangered ground squirrel that is in danger of going extinct—the northern Idaho ground squirrel.”