Wildlife Crossings: Good for Deer, Too

The number of deer killed on California highways has doubled in the last year. Looks like mountain lions aren't the only animals that stand to benefit from wildlife crossings.

by L. Clark Tate

Nov. 4, 2014—While the weekend rainstorm did little to dampen our historic drought, it did finally rinse my filthy car. Sure the smudgy dirt finish is practically a badge of honor these days, but it did tend to rub off on, well, me. Luckily, “dirt don’t hurt.”

But hitting a deer does. And, according to the UC Davis Road Ecology Center, the chance of the average black tailed deer ending up crumpled on your car’s equally mangled hood doubled this year. Like most other things, you can pin this one on the drought.

The UC Davis Road Ecology Center announced last week that its California Roadkill Observation System (CROS) is recording the highest number of deer-versus-vehicle showdowns this year since the program began in 2009. The system, the largest of its kind, sources data from students and citizen science volunteers to track the location and species of victims, i.e. roadkill, throughout the state.

CROS found that the incidence of deer collisions followed a consistent pattern during non-drought years (2010 to 2012). Each year, numbers spiked around October during the rut, or mating season, when bucks roam around seeking does with (presumably) very pretty eyes.

Last year, though—the start of the dry spell—saw a doubling of collisions in October, and this time the spike didn’t subside. In 2014 the numbers (controlled for volunteer fluctuations) have doubled in every month of the year, meaning that any given deer is twice as likely to be hit this year as in years past.

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It’s unlikely that traffic alone is to blame. “Pretty much every year traffic increases by a few percent, but that wouldn’t give you a doubling,” states Dr. Fraser Shilling, Co-Director of the Road Ecology Center.

Shilling thinks that last year’s October spike and this year’s record numbers are related to the drought, which may force animals to move around more in search of food and water. This is a serious problem when food or water is on the far side of a screaming death-strip of highway like California State Route 17.

This is also an expensive problem. Each year the California Highway Patrol (CHP) is called to an average of 1,000 deer strikes in California; each incident costs about $6,600 (ranging from $500 to $20,000). Conservatively, that’s $6.6 million a year without accounting for the human loss (around 100 injuries and 10 deaths) or personal injury lawsuits. But the CHP isn’t involved in every incident. Based on CROS’s data, Shilling estimates that at least 10,000 to 15,000 deer are stuck and killed each year. Doing the math, then, the cost of deer strikes to California motorists is more like $60-90 million a year.

About those lawsuits: In 2005 a motorcyclist successfully sued Caltrans for $8.6 million after colliding with a wild boar on Highway 1 in Monterey County, according to Shilling and Inside Bay Area. The money was awarded for what the prosecution claimed was “bureaucratic indifference of the highest form;” i.e., not stopping wild boars from crossing Highway 1.

How do you stop the wild boar from crossing a road? Presumably the same way you stop a deer, puma or chicken: “For [Highway] 17, a few more [wildlife] underpasses and some fencing,” says Shilling.

“The lesson there is that the cost of not doing anything is actually more than the cost of fixing the problem,” says Shilling. “We can afford to fix this problem."

So why don’t we?

Actually, someone is working on that. The Land Trust of Santa Cruz County is in the midst of a land acquisition valued at $5 million that would spark the building of Highway 17’s first wildlife corridor, beneath Laurel Curve. Sadly, another mountain lion died there Oct. 30, 100 yards from the proposed underpass. Caltrans will pay for the underpass construction, which is not expected to interrupt the flow of traffic.

Stay tuned: this February the Fourth Biennial California Connectivity Forum (as in connecting wildlife habitat) will be co-sponsored by the Road Ecology Center with support from Caltrans.

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