Safe Passage

The I-40 Pigeon River Gorge Wildlife Crossing Project

research

Spring signals a time for elk movement in the mountains

Elk 30216 and her calves throughout the years. During Safe Passage’s road ecology research in the Pigeon River Gorge, GPS collars revealed multiple years of one mother elk’s journey to and from her calving area.

While the elk population in and around Great Smoky Mountains National Park does not migrate, they do make some relatively longer seasonal movements. In these spring months, pregnant females will move away from their herd to give birth in isolated areas. Cows usually carry one calf and give birth in late May through June. In late summer when the calf is large enough, the pair will rejoin their herd, just in time for the rut (mating season) that occurs in late September through early October.

During our road ecology research in the Pigeon River Gorge, elk monitoring with GPS collars revealed multiple years of one elk’s journey to access her calving area. In both years of monitoring, she left the Cataloochee Valley in early spring and crossed the interstate to access her calving area north of the roadway.

In late summer, the cow and her calf would begin their journey back to the park, again having to navigate crossing I-40. In the two years of monitoring, this elk crossed I-40 107 times, with the majority of those crossings occurring at the Tennessee–North Carolina state border, where the Appalachian Trail crosses under the interstate via a road bridge, and also across a road surface just north of that area. 

In the map to the right, you can see her many crossings throughout the years — which she made both with and without her calves in tow, depending on the time of year. Each dot on the map represents the hourly location of this particular elk, Elk 30216.

— Liz Hillard, Safe Passage Co-Research Lead

Safe Passage research revealed the annual journey of one female elk, including 107 trips across I-40. Click the image to enlarge.

Research results unveiled for Safe Passage project area, providing framework for wildlife–vehicle collision prevention

The burden imposed by I-40 on wildlife habitat connectivity and transportation safety makes the Pigeon River Gorge a national priority site for wildlife–vehicle collision mitigation.

On June 29, two partners of the Safe Passage Fund Coalition — Wildlands Network and the National Parks Conservation Association — released their official report, Road Ecology Research and Mitigation Strategies to Improve Wildlife Connectivity and Human Safety along I-40 in the Pigeon River Gorge.

The much-anticipated report details the findings of more than three years of roadside research in the I-40 Pigeon River Gorge project area combined with analysis of 20 years of historical data. The study was one of largest road ecology research projects ever completed in the eastern United States.

The report was authored by a team of cooperating researchers and scientists:

  • Liz Hillard – Ph.D., Senior Wildlife Biologist, Wildlands Network
  • Steve Goodman – Conservation Biologist, National Parks Conservation Association
  • Ron Sutherland – Ph.D., Chief Scientist, Wildlands Network
  • Jeff Hunter – Southeast Regional Program Manager, National Parks Conservation Association

Based on the research findings, the report provides 20 detailed mitigation recommendations for improvements to existing structures or creation of new structures throughout the Gorge, and calls for installation of a system of strategically placed wildlife fencing. Additionally, through consensus, the report’s authors provide seven “top priority” recommendations, including key opportunities to construct wildlife overpasses and install larger culverts under the highway.

Click here to read the executive summary of the report, and click here to read the report in full.

READ THE SUMMARY

The research provides the framework for mitigation strategies to both improve existing structures and construct new wildlife-specific structures to reduce wildlife–vehicle collisions (WVCs) and increase wildlife habitat connectivity.

Science Blog: Do animals behave differently around busy roadways? Yes, observation shows.

Observations in the Safe Passage study area and beyond have begun to show that wild animals are keenly aware of the threats associated with roadways.

Safe Passage researchers have observed what appears to be heightened bear vigilance near the highway (see Figures 1A-1C). Researchers in other parts of the country have shown that GPS-collared black bears approaching roads, especially high-volume highways experience increased heart rates (Ditmer et al. 2018) and higher movement speeds (Zeller et al. 2020). 

Roads sometimes serve as barriers and, other times, as mortality traps. It is an ongoing practice in risk/reward evaluation — for food needs, breeding opportunities, etc. — that bears and other wildlife must make when traversing landscapes infused with roads.

Bears observe and approach Interstate 40 with caution

Figure 1A. An adult black bear observing Interstate 40 one hundred feet away.
Figure 1A. An adult black bear observing Interstate 40, from 100 feet away.
Figure 1B. A young black bear observing Interstate 40 one hundred feet away.
Figure 1B. A young black bear observing Interstate 40, from 100 feet away.
Figure 1C. Bear approaching and returning from Interstate 40 seventy feet to the right.
Figure 1C. Bear approaching and returning from Interstate 40, from 70 feet to the right.

Though data collection is not complete, near the highway, Safe Passage has so far observed fewer sows with cubs, fewer sibling-and-adult interactions and fewer of other normal behaviors. This sharply contrasts with observations made at a distance from the highway, where less stressful and less human-disturbed environments show bears being bears — playing or showing aggression, climbing trees and marking surroundings with their scent (see Figures 2A-2C). 

Farther from the highway, bears relax and play

Figure 2A. Bears wrestling in Great Smoky Mountains National Park two miles from Interstate 40.
Figure 2A. Bears wrestling in Great Smoky Mountains National Park two miles from Interstate 40.
Figure 2B. Adult male black bear sitting just before dusk 700 feet from Interstate 40.
Figure 2B. Adult male black bear sitting just before dusk 700 feet from Interstate 40.
Figure 2C. Juvenile black bear climbing tree 1000 feet from Interstate 40.
Figure 2C. Juvenile black bear climbing tree 1000 feet from Interstate 40.