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Research: When Vehicles and Mammals Collide 3/4/2020

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An elk crossing the road while cars wait. Photo by Noel Reynolds.

When humans and wildlife attempt to share the road, it doesn't always bode well for the mammals. To date, the impact of collisions between vehicles and animals has been calculated simply by relying on the number of carcasses observed on the road. A study published in a recent issue ofLandscape and Urban Planning offers a clearer impact of vehicle mortality on mammals for the past 50 years and suggests clues to ensure the future of North American mammals and humans.

Using a novel approach, the multi-institution team of scientists analyzed a comprehensive review of 421 telemetry-based studies that monitored 34,798 individuals across 66 species. Radio-telemetry allows researchers to monitor an individual animal via handheld radio signal tracking or remotely downloaded GPS locations. If an animal is killed, researchers are able to determine the specific cause. By knowing the different mortality sources of individual animals within a population, a proportion of mortality from vehicle collisions can be derived, as opposed to observation alone.

"Vehicle mortality is not novel to mammal population, but the rate at which it occurs is increasing," said Dr. Jerrold Belant, Camp Fire Conservation Fund Professor in the SUNY College of Environmental Science and Forestry's (ESF) Department of Environmental and Forest Biology, and one of the study's authors. "Over the 52-year study period, vehicle mortality increased four-fold for North American mammals, from three percent in the first decade (1960s) to 12 percent by the last decade (2010s). Not surprisingly, not all species are impacted in the same manner."

Mammals with omnivorous diets suffered greater vehicle mortality than carnivores or herbivores.

"The greater foraging potential near roads for omnivores compared to herbivores may result in their increased use of roadside environments and lead to greater wildlife mortality via vehicle collisions," said Dr. Jacob Hill, research scientist from ESF. "As dietary flexibility is positively associated with mammal adaptability to human-modified areas, omnivores may be more likely to inhabit areas where roads are present, also contributing to higher vehicle mortality rates."

The increased mortality caused by vehicles has the potential to impact overall population dynamics.

"Individuals killed by vehicles often have better body condition than those killed by predators," Hill said. "As body condition is often linked with fertility, vehicle mortality may alter population dynamics by removing individuals with the highest reproductive potential."

The study recommends management techniques, with the goal of reducing the availability of food in roadside environments.

"Habitat management or removal of carrion may decrease risk of vehicle collisions," Hill said. "As human developments and road networks continue to expand, the importance of understanding vehicle mortality risks is exceedingly necessary for both conservation of North American mammals and human counterparts alike."

Dr. Travis DeVault, associate director of research, at the University of Georgia's Savannah River Ecology Laboratory also contributed to this research.

Read the full journal article at: https://doi.org/10.1016/j.landurbplan.2020.103746