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Coyote mortalities decreased 88 percent following the implementation of Disrict 7's mitigation measures to improve habitat connectivity.

Wildlife-Friendly Widening: Park Service Says SR-23 Mitigation Measures are Working
by  Kelly Markham
Issue Date: 09/2012

Click on photos to enlarge and read captions.

Why did the chicken cross the road? The traditional response to this age-old joke is that the peripatetic chicken crossed the road to get to the other side. The Environmental Planning answer: The chicken didn’t cross the road. He used the culvert under the road, which had been installed to reduce habitat fragmentation and preserve healthy, genetically diverse animal populations that had been threatened by a freeway widening project.

Which is not to say that there are many chickens crossing freeways in District 7, nor that freeway improvements are a bad thing. For motorists, widening a freeway can mean faster travel times, reduced congestion and improved mobility. But for the animals who live in the surrounding areas, widening a freeway often creates a destructive barrier — a barrier that impedes mobility, fragments habitat, restricts gene pools, and increases mortality. In extreme cases, a man-made barrier can render some wildlife populations vulnerable to collapse.

Caltrans has long worked to minimize these impacts, mostly with positive results. Case in point: the mitigation measures used for the Moorpark Freeway (SR-23) widening project. In a study recently completed by the National Park Service (NPS), Caltrans’ efforts to improve wildlife movement were found to be effective.

“Caltrans is committed to improving critical wildlife crossings in the region,” said Senior Environmental Planner Barbara Marquez. “With the National Park Service study, we now have data that clearly demonstrate that these mitigation measures are working on SR-23.”

In 2008, Caltrans completed a two-year project that widened SR-23 from four lanes to six lanes, adding one lane in each direction between Thousand Oaks and Moorpark. As part of the environmental mitigation for the project, District 7 implemented three measures to enhance wildlife movement across a two-mile stretch of SR-23 between Olsen Road and Tierra Rejada Road: 12 one-way gates, three culverts that provide clear passage under the freeway, and exclusion fencing that funnels animals to the culverts. Both the widening project and the mitigation received a 2009 Excellence in Transportation Award. But it’s only now, with the completion of the NPS study, that we know how effective the mitigation measures are.

As part of the $90,000 Caltrans-funded study, NPS monitored wildlife movement before the widening project began in 2004 and after it was completed in 2011. NPS biologists conducted road mortality surveys by driving the two-mile stretch of SR-23 three times a week and using remotely triggered infrared cameras to monitor animals’ use of culverts and one-way fences.

The study showed the mitigation succeeded in increasing culvert use by medium-size mammals and reducing road mortality for coyotes. Specifically, successful wildlife crossings increased sixfold and coyote mortalities decreased 88 percent. Additionally, the photos captured of animals using the culverts and gates serve as a reminder of just how smart and adaptable animals are. For example, photos show that some animals figured out how to pass through the one-way gates the wrong way, though they had a little help from two-legged mammals.

“There were numerous instances of animals going through the one-way gates the wrong way — not just once, but multiple times,” said Marquez. “Most of these gates were damaged by people going through them, so the animals had an easier time passing through the wrong way.”

And then there were the bobcats. While coyotes, raccoons and skunks used the culverts to cross (and to forage, in some cases), the bobcats used them as a sort of Bobcat Lounge. They napped in the culverts, cooled off in them on hot days, and even hunted in them before exiting the same way they came in.

Small animals, however, knew to be wary. For the most part, rabbits, squirrels and mice didn’t use the culverts, which were the equivalent of a dangerous neighborhood populated by murderous thugs (e.g., bobcats!). There wasn’t sufficient coverage for these small prey species, and they steered clear. Some opted to cross the freeway instead — with deadly results. Road mortality for rabbits increased fourfold during the study period, probably because the two additional lanes made it even more difficult for them to cross safely.

On a certain level, the animals told us through the study what they need Caltrans to do to improve habitat connectivity. In the small moments of their lives captured by the cameras, in the holes dug under fences, in the bodies picked off the pavement and even by their absence, they point us toward improvements that would make our mitigation measures more effective for them.

For example, they tell us that the exclusion fencing should be inspected regularly for breaks and that it should be eight feet tall in all locations. They tell us that one-way gates need to be modified to prevent animals from going through the wrong way and to increase their effectiveness for smaller animals. Gates for people should be installed as well to discourage them from using (and damaging) the wildlife gates.

It’s also clear that culverts need to be cleaned out regularly to ensure that animals can use them, and that installing smaller scale cover (such as small pipes or logs) would allow small animals to use them as well.

As the NPS study indicates, there are many promising strategies that enhance wildlife mobility in regions fragmented by roads, but there are also formidable challenges.

“The real issue for us when it comes to improving wildlife movement is funding,” said Marquez. “These projects are usually not a priority. But if we don’t try to correct the situation now, there will be less connectivity, less biological diversity, and less wildlife. And once it’s gone, it’s hard to get back.”

As part of the environmental mitigation for the SR-23 widening project, District 7 implemented three measures to enhance wildlife movement across a two-mile stretch of SR-23 between Olsen Road and Tierra Rejada Road: one-way gates, exclusion fencing and culverts. Caltrans' mitigation measures allowed these raccoons and many other animals to cross the newly widened freeway safely. The NPS study showed that successful wildlife crossings increased sixfold. This bobcat is one of many animals who went through the one-way gates the wrong way. In many cases, the gates were damaged by people who used them. Exclusion fencing funneled animals to culverts that would allow them to cross under the freeway.