Add to this a steady increase in highway traffic, and the stage is set for a daily conflict between vehicles and wildlife. The result can prove deadly for both parties. Roughly 200 people also die each year in wildlife-related traffic accidents, usually after hitting deer. This statistic means that deer are the most dangerous animals in North America.
California's Highway 89 offers a classic example of animal-auto encounters. The twenty-five-mile Scenic Byway runs through the lush meadows and dense conifer stands of the Tahoe National Forest. Its western edge borders the NRS's Sagehen Creek Field Station. The highway also happens to bisect the migration route of the Loyalton-Truckee mule deer herd.
From time immemorial, the herd has made its way between summer feeding grounds at the Sierra crest to lower elevation wintering habitat. But nowadays, between 4,000 and 6,000 cars travel Highway 89 each day, making the trip extremely perilous for everyone involved.
Habitat fragmentation and vehicle collisions have already taken a heavy toll on the herd. "In 1982, when the California Department of Fish and Game (DFG) wrote its last herd management plan, the population was about 7,000 animals. Using similar but more advanced population estimates, we calculate that we have around 3,000 now," says Sara Holm, a DFG wildlife biologist who monitors the Loyalton-Truckee herd.
In recent years, however, a number of local, state, and federal officials, academics, and representatives of nongovernmental organizations, including Sagehen Creek Field Station, all realized they were concerned about traffic and wildlife. In 2003, they banded together as the Highway 89 Stewardship Team to engineer better solutions to stem the carnage.
"Highways and development are reducing deer populations, and we're trying to arrest that decline. We are hoping not only to maintain the ability of the animals here to migrate, but also to help restore their numbers," says Sandra Jacobson, a wildlife biologist with the USDA Forest Service's Pacific Southwest Research Station.
The team's first order of business was to determine where deer are most likely to cross the road. The California Department of Transportation (CalTrans) offered an obvious place to start. Since 1979, local maintenance workers have maintained a record of where they have removed dead deer from the highway. An analysis of the database showed that, over the past 31 years, an average of 32 deer carcasses were removed each year along Highway 89.
Recorded kills are probably just the tip of the iceberg, Holm explains. Some deer are hit, but die off the road. Other deer are scavenged by predators and pulled away. The workload of road maintenance crews can prevent them from picking up a carcass. Finally, fawns may not survive after their mothers are killed. Mapping the collision sites revealed clusters of deaths in several places, including two natural drainages.
Holm has provided additional information by tracking the movements of live deer. To monitor the population, she tranquilizes herd members and fits them with collars equipped with GPS. When the animals die or lose their collars (which fall off in about a year), Holm recovers the instrument and downloads the data. "The collars are showing us exactly where the deer cross the highway and in what numbers. This helps us place crossing structures where they will make the most difference," she says.
The mapping data demonstrated that while some deer follow drainages across the road, others move across in a sheet-flow pattern. This movement pattern is common to many landscapes that lack barriers, such as steep canyons and sheer cliffs.
When Holm's mapping data is coordinated with wildlife habitat maps from the USDA Forest Service and U.S. Geological Survey topographic maps of the area, the team narrowed down the most promising places to site a crossing structure. The analysis considered the movement needs of a variety of native animal species, including deer. As luck would have it, Sierra County supervisors had already applied for a federal grant to enhance wildlife movement across Highway 89. Together with additional CalTrans funding, the group was able to build its wildlife undercrossing at a natural drainage.
Located at Kyburz Flat, the crossing consists of a 12-foot-high, 19-foot-wide steel arch. The $732,000 wildlife underpass was completed and dedicated in June 2009.
The next phase of this underpass project will involve fencing the edges of the highway to funnel animals toward the tunnel. Construction of the fences will occur between 2012 and 2013. Each section will be made from different materials to learn how effective each is at channeling wildlife. "Different species have different fence-foiling behaviors. Some push through, while others dig under, climb, or jump over," Jacobson says.
The durability of each type of material is also a factor. "Winter is hard on fences here. Snow moves downhill like a mini-glacier, and if you put up a chain-link fence, the snow here will just eat it over time," says Jeff Brown, manager of Sagehen Creek Field Station. The ideal fence would also maintain the rustic beauty of the area.
The difficulty of meeting these criteria, plus the high cost of fence installation and upkeep, creates opportunities for the Highway 89 Stewardship Team to explore alternative methods of redirecting wildlife. Surfaces that deer avoid, such as boulder fields or the slippery face of sheet metal, could work equally well.
In most places, completion of the underpass and its fencing would mark the end of this story. But the Highway 89 Stewardship Team is just as interested in conducting road ecology research as it is in building crossing structures. "While we're doing mitigation for the deer, we want to learn something about what makes these measures successful," Jacobson says.
"This stretch of 89 is pretty indicative of over 300,000 miles of highway in the United Sates. What is learned here has the potential to have really broad applicability nationwide," Brown adds.
The team is doing all it can to monitor wildlife interactions at the underpass and along several small culverts that already exist along the highway. Motion-detector cameras set up near the tunnel have filmed deer and bear that venture near its mouth. Meanwhile, metal plates dusted with soot have recorded the paw prints of passing species.
The monitoring effort provided a teaching opportunity for local high school students even before the large underpass was constructed. For three years in a row, while grant money was available, Sagehen hosted seven to eight students from Sierra County schools for a summer educational program. The teens reviewed the motion-sensor camera photos and the soot-plate tracks to document the types and frequencies of animals crossing the highway and using existing culverts. They've documented mice, chipmunks, and other animals using these smaller structures.
Coming cyberinfrastructure improvements at Sagehen should aid the project further. A data tower soon to be installed at the reserve will allow the team to collect streaming video from webcams at the undercrossing.
Webcam analyses, Holm says, would "help us pinpoint behavioral adjustments animals make to highway noise, the structure itself, or other variables. Live video will show us if animals are tentative about going through the crossing, or whether there's a difference between the behavior of marked deer that have already used it and deer who see it for the first time."
Early webcam data were being analyzed by a visiting professor at the UC Davis Road Ecology Center until he departed for another position. The team is now seeking an alliance with another biologist interested in land planning for wildlife to help study the video. The permanent cameras installed with help from local students are now maintained by Highway 89 Stewardship Team members.
Future plans call for developing an acoustic map of the underpass. This information will help researchers determine how to dampen noises that animals find threatening. Signs that flash and warn drivers whenever animals are detected on the roadway may also be installed.
"We want to see what critters do when they approach a barrier like Highway 89 — how they use the landscape and make a decision on where to cross the road," says Sagehen manager Brown. "By understanding their psychology, we may find easier ways to manage the problem than putting up fences and bridges. But until we get a better sense of what the animals are thinking and doing, we won't know the best strategy to manage this." — KMW