A Silver Lining to the 2023 Illinois Fisher Story

A silver lining to the untimely demise of a fisher (Pekania pennanti) on an Illinois roadway in 2023 is that it will become an information gold mine for wildlife biologists. The results of the extensive testing conducted on the fisher’s remains will provide wildlife professionals with a solid baseline of knowledge about a species that has not lived in Illinois since the mid-1800s.

Initial findings from the necropsy confirmed that the fisher was a young, reproductively active male in excellent condition that died as a result of blunt trauma to the head and thorax, consistent with being struck by a vehicle. Low levels of protozoan and metazoan parasites were identified, but that finding was not unexpected, as free-ranging wildlife often have a parasite load. What intrigued biologists is what they might learn from the other testing.

In addition to the necropsy, further testing was done including a disease exposure work-up, stable isotope analysis and cementum ageing. The diagnostic services were performed by the world-renowned Zoo Pathologists from the Zoological Pathology Program, a collaboration between the University of Illinois College of Veterinary Medicine and several private and public entities, including zoos, federal wildlife agencies and conservation organizations around the world. The results of these assays will help biologists understand the potential for disease movement as well as insight into what potentially drives fishers to move to new habitat across the midwestern landscape.

Zoonoses

Biologists determined that the fisher traveled from Wisconsin, but what was unknown was what sort of diseases it might have been carrying as it crossed state lines. Hence the need for testing in support of the multidisciplinary One Health approach. One Health is a collaborative approach that recognizes that the health of people is connected to the health of wild and domestic animals and the environment.

While these sorts of investigations are endlessly fascinating to wildlife biologists, most people might wonder why such extensive testing would be done on just one animal? Even if it was a rare animal. The short answer is protecting public health and safety.

These professionals are concerned with contact rates and the spread of disease, and so they are interested in areas where infected humans or animals may encounter each other. Having that sort of data can help to reduce risks to public health.

According to the World Health Organization, 60 percent of emerging infectious diseases globally are zoonoses coming from wild or domestic animals, and 75 percent of the over 30 new human pathogens detected in the last three decades originated in animals.

Viruses comprise the most abundant entities on Earth, and as part of the microbiome they play essential roles in immunology, evolution, biogeochemical cycles, health and disease pathways. They can cause infectious diseases that impact human and animal health. Which is why virus discovery and the study of their replication and infection mechanisms is essential to understanding the emergence of viral pathogens.

The Hunt for Novel Viruses

Viral metagenomics testing was conducted on the fisher’s lung and brain tissues. The fisher was also tested for infection within the Morbillivirus genus which includes species that cause measles in humans and canine distemper in a range of carnivores, including fishers. In the case of the fisher that made its way to Illinois, the viral metagenomics testing and Morbillivirus testing found no evidence of viruses. Due to the condition of the animal, rabies testing could not be performed.

COVID Testing

Fishers, like mink, are members of the Mustelidae family. So, it isn’t surprising that biologists also wanted to test the fisher for the SARS-CoV-2 virus. Near the beginning of the COVID outbreak, the relationship between the virus and mink was making international news.

In 2020, in an effort to stem the spread of the virus SARS-CoV-2, which causes COVID-19, Denmark culled 17 million mink on farms where they were raised for their fur. Scientists were worried that mutations in the virus might reduce the efficacy of the COVID-19 vaccines being developed. The mink had been shown to be highly susceptible to the virus, having been infected by a farm worker with COVID-19, and there had been several documented cases of mink-to-human transmission. Other countries, including Spain, Sweden, Italy, and the United States, also culled mink populations at affected farms.

Human and animal health are interdependent. As the SARS-CoV-19 virus is a zoonosis (disease transmission from animals to humans), has been found in a variety of species of free-ranging wildlife, and has been documented as a reverse zoonosis (disease transmission from humans to animals) it was proactive to test the fisher for COVID. Testing confirmed that the Illinois fisher was not infected with the SARS-CoV-2 virus.

Stable Isotope Analysis

In the past, if a biologist wanted to know what was included in a wild animal’s diet, they would have to commit to the time-consuming process of observing the animal to see what it ate, or the rather more unpleasant tasks of collecting the animal’s feces or stomach contents for analysis. Today, researchers can conduct stable isotope analysis using an animal’s whiskers. Stable isotope analysis allows researchers to use the whiskers to identify markers of certain foods, which can then be used to partially reconstruct an animal’s diet. Biologists know approximately how fast a fisher’s whiskers grow, so the whiskers can be cut into sections that correspond to about a week’s worth of growth. This provides a week-by-week snapshot of what the animal ate and can provide a 12-18 month diet history.

Why would that be important to biologists? Climate change is altering habitat conditions which will have future impacts on where and how wildlife move across the landscape. A study of fishers in California using stable isotope analysis and long-term monitoring found that fisher survival was sensitive to increasing temperatures and diet. So, there is value in knowing what the diet of the Illinois fisher included.

Additionally, in the northern portion of their range fishers are known to prey on porcupines, but with no porcupines available in Illinois, any fishers dispersing here would have to adjust their diets. Studies have shown that in areas where porcupines and snowshoe hares are unavailable, fishers will consume squirrels and raccoons, as well as birds, reptiles and plants. What the Illinois fisher consumed is still to be determined but the results will provide biologists with important clues about fisher habitat selection.

The results of the stable isotope analysis are still pending and will be shared once they become available. That data will be square one for future biologists to refer to if other fishers eventually make their way into Illinois.

Cementum Ageing

While the necropsy estimated the fisher to be about three years old, cementum ageing will confirm or deny that finding. Cementum ageing is the gold standard for estimating an animal’s age and is more accurate than tooth wear. Some of the tooth root of the fisher was sent to Matson’s Laboratory in Montana for testing. There it will be microscopically sectioned and analyzed. The roots of the tooth have rings which can be counted to determine the fisher’s age, very similar to how trees are aged by counting their tree rings. These results will also be shared once the cementum ageing is completed.

Report Fisher Sightings in Illinois

While fishers were once native to Illinois, the population seems to have been extirpated from the state by the 1860s. But as populations in other states expand their range, we may see other fishers make their way to Illinois. You can help biologists track this potential range expansion by reporting fisher sighting to the Illinois Department of Natural Resources at: https://wildlifeillinois.org/report-sightings/report-unusual-animal-sightings/. Be sure to include photos so that potential sightings can be confirmed.

---

Laura Kammin is a Natural Resources Specialist with the National Great Rivers Research and Education Center. She formerly held positions at Illinois-Indiana Sea Grant, University of Illinois Extension, Prairie Rivers Network and the Illinois Natural History Survey. She received her master’s degree in wildlife ecology from the University of Illinois, Urbana-Champaign.