Understanding the Ecology of Recently Recolonized Bobcats in North-central Illinois

Photos by Clayton K. Nielsen.

Bobcats (Lynx rufus) are a widely distributed, medium-sized carnivore species, serving as a top predator in many ecosystems across North America. Bobcat habitat was abundant throughout the midwestern U.S. prior to the 19th century, however European settlement thereafter converted forests, prairies, and wetlands to predominately agricultural and urban landscapes. Along with overexploitation, this loss of habitat led to the near extirpation of bobcats in many areas of the Midwest, including Illinois. In response, bobcats became a protected species in Illinois in 1972 and were added to the state’s list of threatened and endangered species in 1977. Bobcats remained rare in Illinois until the late 1990s when they began recolonizing the Midwest and were delisted in 1999 to nongame status. Recent studies suggest bobcat populations across North America are stable or even expanding in some locations, including Illinois where they became harvestable in 2016 with harvests of less than 400 individuals each year.

Urban and agricultural land uses continue to fragment bobcat habitat in the Midwest where their recolonization has only recently begun. Along with other mammals, this fragmentation may have consequences for resource selection and movement, reproduction, survival and dispersal of recolonizing bobcats. Although bobcats have been studied in similarly fragmented landscapes, there are no such studies from north-central Illinois, which represents the last portion of Illinois to “fill in” with bobcats.

Funded via the Federal Aid in Wildlife Restoration program (Project W-213-R), administered through the Illinois Department of Natural Resources (IDNR), we began studying bobcat ecology in Peoria and Bureau counties in late 2022 and will continue through 2026. Our specific objectives are to (1) estimate survival, (2) quantify dispersal movements, (3) estimate reproductive parameters, (4) quantify spatial ecology and habitat selection, and (5) evaluate genetic structure and natural recolonization. Our goal is to provide the IDNR with information to support bobcat management in Illinois.

Bobcat Capture and Collaring

The foundation for our data collection is capturing and fitting bobcats with GPS collars, which allow us to track their movements and survival. We capture bobcats from November through March using wire cage traps and padded foothold traps; all capture and handling activities are approved by the Institutional Animal Care and Use Committee at Southern Illinois University. Traps are baited with various gland lures, meat from road-killed animals, bobcat urine and visual attractants. Captured bobcats are chemically immobilized and when bobcats are manageable, we determine sex, weight and age. Adult bobcats are then fitted with GPS collars equipped with a release mechanism to drop off one year after activation. Collars are programmed to record GPS locations once every 2 hours and those locations are sent to us via satellite once daily. We also collect tissue samples from each bobcat for genetic analysis. Bobcats then wake up from the procedure and go about their merry way to do what bobcats do…but now…we are recording their behavior! Thus far, we have collared 29 adult bobcats and have collected more than 50,000 GPS locations from them.

Survival Monitoring

If the GPS collar is working and the bobcat stops moving for more than 6 hours a “mortality alert” notification is received. If the GPS collar stops working the bobcat’s survival can be monitored using very high frequency (VHF) radiotelemetry, which emits a radio signal (i.e. beeping sound) from the collar that can be heard using a handheld receiver and antennae. This helps us understand where the bobcat is in real-time in case the GPS unit isn’t working. If the bobcat has stopped moving, the signal from the collar will beep faster, alerting the listener that the bobcat may have died. Using these tools, we can respond relatively quickly to bobcat mortality events to determine the cause of death and accurately estimate annual survival rates. We have thus far confirmed five mortalities during the study, three caused by vehicular collision, one by legal harvest and one unknown.

Kittens!

Like many medium-to-large mammals of North America, bobcat mating typically occurs during winter (e.g. December to May, with peaks in late winter) resulting in a birthing peak during April through June. During these spring and summer months, we monitor GPS collared adult female bobcats for signs of denning. Signs include “quiet days” where the GPS collar does not upload locations, likely due to the female denning under brush. GPS locations that are uploaded will usually appear to be clustered in a small area, indicating the female is staying near her kittens. Once we estimate the kittens to be around 3–4 weeks old, we carefully approach the suspected denning location and attempt to locate kittens. If we do find kittens, we determine the litter size, sex of each kitten, and confirm kitten ages based on tooth emergence and weight. All kittens are microchipped, and if large enough, fitted with a small, expandable VHF collar designed to grow with the individual and fall off within one year. We monitor collared kittens for as long as we can, ideally for 6 months. We monitor each kitten’s survival daily and estimate locations once per week until 2 months of age. When kittens are 2 months of age and older, we monitor survival and determine locations weekly.

About 6 weeks after collaring kittens we return to den locations to measure fine-scale habitat characteristics that we will use to understand den site selection. We specifically measure canopy cover, ground cover, coarse woody debris, basal area and aspect. These characteristics, among others, are known to be important for other carnivore species as they provide concealment and protection from predators and inclement weather, as well as thermal regulation.

Home Range and Habitat Selection

GPS data from collared bobcats are used to understand bobcat habitat and space use. We are comparing habitat selection and home range sizes of bobcats in the more fragmented north-central region to those of bobcats in southern Illinois where available habitat is considered less fragmented and more suitable (we have bobcat data from this region of the state, as well). This will provide information regarding differences and drivers of habitat and space use between these populations and environments. Furthermore, data from collared 1- to 2-year-old individuals, the primary dispersers in bobcat populations, will be used to determine habitat characteristics important for long distance dispersal movements, overall landscape connectivity, and important travel corridors.

Information for Management

Upon completion in 2026, our project will provide the IDNR with information to support decision-making regarding bobcat management in Illinois. Estimates of survival rates and causes of mortality will indicate potential limiting factors for bobcats. Knowledge of dispersal movements and habitat selection will elucidate how bobcats use this largely agricultural landscape. Wildlife biologists also will be able to compare our results from the present study with prior bobcat research conducted in Illinois during the past 30 years. Bobcats are thriving in Illinois given light human harvest levels, ample prey, and generally suitable habitat through much of the state—who would have predicted this back when bobcats were first protected in Illinois more than 50 years ago?

Thank You

Our research could not be possible without the cooperation of numerous Illinois landowners, so thank you for access to your properties! If you are a bobcat trapper or hunter and wish to contribute a tissue sample to our genetic work, please contact us at siubobcats@gmail.com, (231) 838-9051 or https://ncillinoisbobcats.siu.edu.

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

Guillaume Bastille-Rousseau is an assistant professor with the Cooperative Wildlife Research Laboratory of SIU. His research focuses on the spatial wildlife ecology of terrestrial species, mostly focusing on animal movement.

Brent Pease is an assistant professor in the Forestry Program at Southern Illinois University where he researches and teaches topics in wildlife conservation and management. Dr. Pease received his doctorate degree from North Carolina State University in Fish, Wildlife, and Conservation Biology. A native of southern Illinois, Dr. Pease enjoys being back in the region to raise his family among the public lands and state parks of Illinois. Learn more about his research at www.peaselab.com.

Ellen Audia is a Ph.D. candidate in the Cooperative Wildlife Research Lab at Southern Illinois University. She is researching the spatial ecology and movement of bobcats in north-central Illinois. Audia received her master’s in Wildlife Ecology from Iowa State University and her bachelor’s in Natural Resource Management and Mathematics from Grand Valley State University located in her home state of Michigan.

Katie Buckman is a Ph.D. student in the Cooperative Wildlife Research Lab at Southern Illinois University studying bobcat demographics. She is originally from Florida, received her B.S. from the University of Florida, and received her M.S. from Florida Atlantic University where she studied bobcat spatial ecology in the Florida Everglades. Buckman aims to pursue a career in academia post-graduation, and her research interests include population dynamics and human dimensions of wildlife research and conservation.