One of the river otters captured on a trail cam by researchers.
This is the third installment in a Q&A series that highlights scientists uncovering the hidden stories of our natural world. Their research in Will County preserves protects biodiversity, informs conservation efforts and deepens our understanding of the environment we share. This feature spotlights river otter research that grew out of studies into the survival of other urban mammals.
From a low of just 100 in the 1980s to more than 11,000 today, the river otter has made a remarkable comeback in Illinois.
Will County has become a hot spot for these apex predators, which feed on fish and frogs along the Des Plaines River from the Forest Preserve District’s Rock Run Rookery Preserve in Joliet north to Keepataw Preserve in DuPage Township.
A coalition including the Max McGraw Wildlife Foundation, The Ohio State University and the Forest Preserves of Cook County is working to track river otters and learn how they survive in urban environments.
On a recent fall morning, Shane McKenzie, a research associate for the foundation, and Nicholas Lusson, a senior field technician for The Ohio State University, trudged through tall grass, their boots squishing in mud, to reach known otter “latrine” sites at Keepataw. There they searched for scat and collected hairs caught on specially designed devices. The scat reveals what urban otters are eating, and the hair DNA provides a kind of Ancestry.com for otter populations in Cook and Will counties.
River otter research began in 2017, building on the 25-year-old Urban Coyote Research Project in Cook County. In Will County, the project is just a year old, with The Ohio State graduate student Cami Vanderwolf analyzing the data.
Here, in their own words, McKenzie and Vanderwolf answer questions about their work:
What is the goal of your research project?
Our main goal of this project is to address gaps in urban river otter ecology information and management in an unbiased manner. River otters are historically known to be avoidant of humans and developed areas, so we want to better understand how river otters are now adapting to living in urban areas. While more urban river otter populations are currently being discovered around the country, there is still little research on urban river otter ecology. We are studying this population to document shifts in river otter behavior in urban areas, such as in their habitat use, movement and diet. Our research uses a combination of invasive and non-invasive sampling methods. Using trail cameras and radio-telemetry tracking, along with hair snaring and latrine sampling, we aim to better understand river otter populations, interspecies interactions and otter urban adaptation strategies.
Why are you surveying river otters in Will County specifically?
The Urban River Otter Project focuses on studying urban otters within Cook County. However, like other species, these animals have the propensity to travel great distances. Using trail cameras, the project identified the presence of river otters in the Cook County Black Partridge Forest Preserve. This preserve shares a border with Will County, so otters freely move throughout this area and Keepataw Preserve. Using a combination of hair snare and latrine sampling methods, graduate student Cami Vanderwolf will use the data to determine river otter diet makeup and population size. Hair snares are devices that snag small samples of hair from an animal when they rub against it. Vanderwolf is also analyzing the best non-invasive ways to study river otters. Non-invasive sampling methods, which minimize human interaction and stress on animals, are becoming more important tools for biologists to study wildlife. Non-invasive sampling is very important in urban wildlife research due to the cryptic nature of urban wildlife species. Camera trapping, scat collection and hair snaring are all important non-invasive methods, but Vanderwolf wants to determine which methods are best for collecting data on urban river otters. These findings can help managers allocate funding and fieldwork time to the most effective sampling methods to conserve urban otter populations. River otters also have been successfully live-captured and implanted with radio telemetry tracking transmitters in the Black Partridge/Keepataw area. We regularly monitor these otters and collect location points using telemetry equipment. Tracking otters will expand our understanding of otter movements and spatial ecology.
What is the farthest you have tracked otter movements?
We have found that the river otters we tagged here have ended up north of us, all the way up to McCook close to the border of Chicago. And we’ve tracked them as far south as the Rock Run Rookery in Will County, which is further south along the Des Plaines River near Joliet. This tracking has allowed us to understand their movements across the landscape.
How long has this study been taking place?
Preliminary research began back in 2016 when the first river otter in Chicagoland was discovered at Sand Ridge Forest Preserve in Cook County. We started a more comprehensive study in 2020 that expanded our camera trapping and telemetry efforts. Efforts to conduct latrine searches and hair snaring in Will County began in early 2025.
What are you looking for in the preserves?
We are continuously relocating our radio-tagged river otters within the preserves to identify what habitat and waterway types they use the most. This information will help us identify new areas where otter populations could expand and help us protect these areas to ensure healthy urban otter populations. We are also routinely searching known latrine sites to collect scat samples and set up hair snares. Because otters are social animals and repeatedly visit and defecate in communal areas, we can easily obtain samples from multiple individuals at a single location. Hair and scat samples will be analyzed to determine what foods urban otters eat and whether they eat human food sources, such as trash or supplemental food, like other urban animals (coyotes/raccoons) are known to do. Additionally, we set up and rotate remote camera traps across several forest preserves to surveil for new otter populations around Chicagoland.
Have you been successful in finding the information you need?
This is an ongoing study. The data collection involving Will County forest preserves will continue until the end of 2025. Since the end of 2024, we have collected more than 150 otter scat samples and 80 hair snare samples from multiple species, including otter.
Are river otters in decline and, if so, why?
No, exactly the opposite. Starting with the Clean Water Act of the early 1970s, water quality in the Chicago area has been improving. It is estimated there were only about 100 river otters remaining in Illinois by the late 1980s. This decline in otter populations was mainly due to overharvest and habitat loss/degradation. In the 1990s, the Illinois Department of Natural Resources initiated a recovery plan and relocated otters from states with strong populations, like Louisiana, throughout central and southern Illinois, including the Illinois River. In 2004, Illinois removed river otters from their endangered species list. By 2009 the Illinois otter population was estimated to be over 11,000. River otters were never reintroduced into the northeast part of the state, so their recolonization into Will County and beyond is a testament to the growth and recovery of river otters in Illinois.
Why is this work important?
River otters are apex predators. Their presence and population growth are an indicator of ecosystem health. The efforts of the last 50 years to improve our waterways through clean water initiatives have improved the health and diversity of fish and mussel prey populations, supporting the viability of river otters in urbanized areas.
What should people know about this work and why it is done?
Urban wildlife ecology is a relatively recent field of academic study. Millions of people live in metropolitan areas alongside a variety of urban mammals. These animals contribute to the ecological balance and biodiversity of a city. Studying urban wildlife helps address human-wildlife conflict, bettering wildlife management and improving the quality of life for the people living there. Animals like coyotes have adapted to urbanization without human intervention, while others like the river otter owe their recovery to conservation efforts and habitat improvement. While river otters have rebounded in great part due to human-led efforts, we can still benefit from their presence in our urban areas, too. River otters are very sensitive to water pollution and other contaminants, so they serve as a bio-indicator species – animals that monitor changes in environmental health and their impact on humans. River otter presence or disappearance tells us how healthy our urban waterways are. By protecting urban river otters, we can also ensure safe and healthy urban environments for us and many other wildlife species.
What future activity will take place?
We will continue hair snare and latrine sampling through 2025. Future research will depend on funding.
Closing
In addition to McKenzie and Vanderwolf, the Urban Otter Project is overseen by Stanley Gehrt of The Ohio State University and Chris Anchor of the Cook County Forest Preserves’ wildlife management department. Together, the team is expanding the understanding of how otters are thriving in the urban landscapes of northeastern Illinois.