Macomb, Ill. — Bobcats in western Illinois are either explorers or homebodies, depending on their sex. Researchers from Western Illinois University report the home range for male bobcats in their ongoing study is 46 miles, while the range for females is only eight miles.
“Overall, both sexes have a range from 3 to 80 miles,” noted the research team of Edward Davis, Tim Swearingen, and Christopher Jacques.
Three years in, the team has collared 38 (20 males, 18 females) bobcats, of which they are currently monitoring movement and survival status of 11 GPS- and 14 VHF-collared individuals. The multi-year study aims to evaluate home range use and the utility of camera traps for estimating bobcat abundance. It also seeks further development of camera survey protocols and evaluation of annual/seasonal survival rates of bobcats across west-central Illinois. Development of camera survey protocols incorporates information on home range use, bobcat capture/recapture rates for varying spatial arrays of camera traps, and habitat data gathered from GPS locations of previously captured animals.
More specifically, researchers use spatial capture-recapture designs to identify individual bobcats based on unique spot patterns within a camera survey grid.
As for bobcat deaths, through February the researchers had documented eight bobcat deaths. Vehicle collisions are the leading cause of mortality and have accounted for four (50 percent) mortality events. Remaining deaths have been attributed to harvest (three) and capture-related factors (one). Estimated annual survival is 51 percent.
Bobcat survival monitoring is ongoing through June 2019 and will evaluate potential effects of sex, age, and habitat variables on seasonal and annual survival rates.
During Phase 1 of the study, which ended in 2017, more than 600,000 images were collected from 140 camera stations deployed across breeding and kitten-rearing seasons from November 2015 to April 2017.
For Phase 2, which runs through 2019, approximately 220 cameras were deployed in January and remained active through March.
Since 2015, approximately 360 camera stations (720 total cameras) have been deployed throughout the four-county region.
Findings by the WIU team during Phase 1:
- Bobcat density estimates were generated using 50 camera stations deployed over a 77-day period. In total, 23 uniquely identifiable bobcats were captured 115 times and recaptured 92 times.
- Bobcats were photographed at 36 of 50 (72 percent) camera stations.
- The bobcat density estimate was 1.44 individuals per 100 kilometers (31 miles), though it ranged from 1.07 to 1.90 bobcats per 100 kilometers.
The physical location of cameras and numbers of capture/recapture events across multiple camera stations are used to create encounter histories of bobcats that walk in front of cameras.
Researchers use this information in combination with locations of radio-collared individuals to generate reliable estimates of bobcat density. Use of remote cameras is less invasive, labor intensive, and costly than other long-term census techniques (trapping and collaring all bobcats in an area).
Phase 2 work is ongoing and final project results will be available during summer 2019.
Bobcat capture methods
Bobcats are captured using nonlethal (cage and foothold) traps. In addition, WIU researchers rely heavily on local trappers to ensure that the desired number of bobcats are captured each year.
To date, 68 percent of WIU’s research animals have been captured by local fur trappers across the study site, which is predominantly private land. Thus, gaining access to private land and building relationships with local landowners and trappers throughout the primary study area (Fulton, McDonough, Schuyler and Hancock counties) is essential.
After a bobcat is radio-collared, researchers use standard telemetry techniques (mounted and hand-held antennas) to monitor weekly movement and survival status.
Researchers then enter animal locations into a Geographic Information System to determine home range size and spatial activity patterns, which aids in the development, evaluation, and future use of camera surveys to monitor bobcat abundance across the state.