A couple of Jackson Hole wildlife researchers who set out to test how well roadside reflectors keep deer away from traffic have made a surprising discovery: White canvas bags are an even better deterrent.
Researchers suspect the effect might have something to do with the white tails of deer.
Corinna Riginos and Morgan Graham recently presented findings from a three-year Wyoming Department of Transportation-funded study that assessed deer-vehicle collisions along three stretches of highway in the Bighorn Basin. The research analyzed the behavior of deer and how frequently they were being hit where post-mounted wildlife warning reflectors were set along the road. As a control, white and black bags were also fitted over the reflectors.
“What we see is we have the highest number of carcasses ... in places where reflectors were covered with the black bags,” Riginos said Monday at a Teton County Library public talk. “We have intermediate levels where the reflectors are exposed, and the lowest levels of carcasses where the reflectors are covered with the white bags.
“The implication here is that reflectors covered with white bags are about 65 percent more effective than reflectors with the black bags,” she said. “That’s pretty stunning, actually. Apart from crossings — overpasses and underpasses — there’s nothing 65 percent effective out there.”
The project also analyzed patterns of deer-vehicle collisions on Wyoming highways between 2008 and 2013, and resulted in a “hotspot map” that summarized the frequency of accidents all around the state.
Deer hit on Wyoming roads cost $44 million to $52 million a year when accounting for injury, damage and lost wildlife value, the study said.
Weighing differences in road characteristics, how deer use the land and habitat, Riginos and Graham found five variables that were the best predictors of collisions.
Traffic volume and the speed limit were the most important factors relating to the nature of the road. Statewide there was on average a doubling in deer hit by motorists when the speed limit went from 55 to 75 mph, and a doubling in traffic volume resulted in a 35 percent jump in collisions, Riginos said.
Places where deer migrated through and wintered were the best predictors of collisions.
As for land use, the presence of cropland made for the likeliest deer-vehicle collision hot spots.
The reflector portion of the study tested the effectiveness of Streiter-Lite red glass “deer delineators” that cost $8,000 to $10,000 per mile to install, not factoring maintenance. That’s much cheaper than wildlife crossings paired with fences, which can cost millions.
The white bags, made from 10-ounce cotton duck canvas, cost even less, just $1.50 a sack.
“Sticking a white bag on a post was much more cost-effective than putting a Swarovski crystal reflector on there,” Riginos said.
The reason why white bags are a better deterrent than reflectors is an open question, but Riginos suggested it could be related to how deer react to various colors.
White, she said, is also the color of the underside of deer tails, which deer flash as a warning sign to other deer.