New Study Shows Impact of Roadkill on World’s Vulnerable Animal Populations

Vehicular collisions are a common cause of death for animals such as the endangered Florida panther and the state’s black bears, and a new international study has quantified how big of threat roads can be to the survival of animal populations around the world.

The study has identified four animal populations globally that are the most vulnerable to extinction in the next 50 years if observed roadkill levels persist:

• Leopard Panthera pardus of North India (83% increased risk of extinction from roadkill)
• Maned wolf of Brazil (34% increased risk of extinction)
• Little spotted cat of Brazil (increased extinction risk ranging from 0 to 75%)
• Brown hyena of Southern Africa (increased extinction risk ranging from 0 to 75%).

The study appears in the journal Global Ecology and Biogeography and is co-authored by University of Central Florida researcher Eric Goolsby.

Roads are essential infrastructure that connects people and circulates supplies but when they intersect with nature, the impact on species survival can be deadly; however, just how deadly has been largely unknown until this study.

Certain traits, such as early age of sexual maturity and large litter sizes, can help species bounce back from the toll of roadkill deaths, says Clara Grilo, the study’s lead author and a postdoctoral research fellow with the Universidade de Lisboa in Portugal.

But for others, such as brown and black bears that have late maturity age and small litters, roadkill can have a big impact on their population.

“Using phylogenetic models, we could predict which species are more vulnerable to roadkill and found that brown bear and black bears are particularly vulnerable,” Grilo says. “If there is at least 20% of the population road-killed it can increase by 10% the risk of local extinction.”

In Florida, vehicle collisions are responsible for 90% of known bear deaths, according to the Florida Fish and Wildlife Conservation Commission.

For the endangered Florida panther, more than 85% of recorded panther deaths were due to vehicles in 2020, according to the Florida Fish and Wildlife Conservation Commission.

Florida panthers share a similar increased risk of extinction with bears based on the study’s data for their species, Puma concolor, where a 10% increased risk of extinction occurs if at least 27% of the population is killed by traffic.

“It is important to protect the diversity of species on Earth because each species has a role in the ecosystems, and the loss of species triggers the loss of other species within its ecosystem,” Grilo says. “Humans depend on healthy ecosystems like healthy soils, forests, grasslands, rivers, oceans. Otherwise, we risk our own health.”

Knowing which animal populations are most vulnerable to extinction by roadkill can inform infrastructure management decisions, such as where new roads will go and how to protect vulnerable animal populations in those areas.

These protections can include combinations of underpasses or overpasses with fencing to guide animals to use those passages, Grilo says.

Breakdown of the study

To perform the study, the researchers used existing roadkill data for near threatened to critically endangered mammal species on six continents — North America, Central, and South America, Europe, Africa, Asia, and Oceania.

Then, taking into account data such as population density and roadkill rates as well as animal traits like sexual maturity age and litter size, the researchers were able to calculate increased extinction risk due to roadkill. This information was then used to create global roadkill vulnerability maps.

Goolsby, an assistant professor in UCF’s Department of Biology and study co-author, was responsible for much of the phylogenetic work that estimated any missing trait values for species in the study by using trait data on closely related relatives.

“We used a missing data imputation approach based on trait correlations and evolutionary relatedness,” Goolsby says. “I developed a software package in the R programming language which allowed us to perform these calculations on large datasets. Our dataset, which consists of multiple traits spanning thousands of species, would have otherwise been computationally infeasible to analyze using previously existing software implementations.”

“Dr. Grilo read some of my publications on efficient phylogenetic comparative methods and asked if it would be possible to take her dataset and use it to try to predict their trait values that we could use to estimate species vulnerabilities to roadkill and extinction risks,” he says. “And I said it would absolutely be possible. So, I joined as a collaborator, and we’ve been working on this project ever since.”

Grilo says the next steps for the research are to develop user-friendly software to display observed roadkill data and show areas where species are more vulnerable to vehicle deaths.

“This will be a valuable tool for road planners and road managers to identify road segments to implement mitigation measures in developing countries in Asia, Africa, and Latin America,” she says. “We are looking for funding to develop the software because we already know how to do it.”

Goolsby received his doctoral degree in toxicology from the University of Georgia. He joined UCF’s Department of Biology, part of the College of Sciences, in 2018.