Cuesta Grade wildlife research tracks critter crossings


Every day, thousands of motorists commute on Highway 101 over the Cuesta Grade. Few are aware that the highway bisects another kind of freeway, one used by wildlife.

Hundreds of animals, large and small, are hit and killed every year by vehicles as they try to cross the major thoroughfare in their quest to find food and mates. The deadliest stretch for large animals is near Tassajara Creek Road.

Five, possibly six, black bears have been killed by vehicles on the Grade since June. The most recent bear was killed Jan. 11. No motorists were injured in any of these collisions.

One or two deer a month are also struck and killed.

Bob Stafford, a Department of Fish and Game biologist in San Luis Obispo County, has worked with wildlife all over the state and says the Cuesta Grade is unique. Many wild animals cross the highway there while migrating between the east and west Cuesta Ridge areas of Los Padres National Forest.

“To be honest, I can’t think of another place where we’ve had as many bears hit in such a small area,” he said.

To complicate matters further, Caltrans is considering installing concrete median barriers at the top of the Grade that could hinder wildlife movement.

Cars hitting large wildlife is both a public safety and natural resource management issue, said Chuck Cesena, a senior environmental planner with Caltrans. The agency is working with Cal Poly biology professor John Perrine to head a yearlong study of wildlife movement patterns along the Grade.

“We want the study to find out more about the situation and identify options for reducing mortality,” Cesena said.

The agency recently installed signs along the highway alerting motorists to be on the lookout for bears crossing the road. Another option under consideration is installing fences that will keep animals out of the highway corridor and channel them to areas where they can safely pass underneath the road.

A railroad undercrossing near the top of the Grade is the biggest safe crossing point. There are also several culverts under the highway that drain rain runoff, which can accommodate big animals, Cesena said.

“Any fencing project will include ramps called jump-outs that allow animals to get back out over the fence in the event they are trapped inside the highway corridor,” he said.

Focus on big animals

Perrine’s study is intended to give state officials a comprehensive look at human-wildlife interaction along the Cuesta Grade. However, the emphasis is on deer, bear, mountain lions and wild pigs.

“Currently, my study is looking at all the larger mammals that might be passing through the Cuesta Grade wildlife corridor and pose a threat to human safety if struck by a vehicle,” he said.

Adult black bears commonly weigh 200 pounds or more.

Although the study is still ongoing, one conclusion seems evident. The top of the Grade is the most active highway crossing spot for the large mammals the study targets.

“The area immediately north of the Grade, near the vicinity of Tassajara Creek, appears to contain a desirable combination of natural land cover without steep slopes, and therefore may be an important crossing point for large mammals,” Perrine wrote in a preliminary report to Caltrans in December.

Gathering data

The study started last May and is scheduled to conclude this spring. It uses four main techniques for gathering information about wildlife in the area. They are:

• Road-kill surveys. Five days a week, two Cal Poly students drive Highway 101 from San Luis Obispo to the Santa Barbara Road exit at the southern boundary of Atascadero and back, a distance of about 12 miles one way.

Along the way, they note every dead animal they see. If the animal is one of the four targeted large mammals, the students stop the car, note its exact location using the Global Positioning System and gather other information about the animal.

Squirrels are far and away the most common animals killed. This could be important because squirrel carcasses attract larger animals and birds of prey, and that creates a collision hazard, Perrine said.

• Camera traps. Seven motion-activated, infrared digital cameras are arrayed near the highway. They photograph any animal that happens by. Some are located at highway undercrossings to get an idea of how much they are used by wildlife. Others are baited with cat food and are intended to inventory as much wildlife in the area as possible.

Since the study began, the camera stations have amassed an impressive collection of pictures of every conceivable animal that lives in the area — 19 different species, in all. This includes one mountain lion, red and gray foxes, coyotes, bobcats, wild turkeys, opossums, bears, squirrels, birds and even the occasional housecat and stray dog.

Because of their effectiveness, camera traps are becoming an increasingly important tool in wildlife biology nationwide, Perrine said. Their effective range is about 12 feet in front of the camera.

The cameras use infrared flash and motion detection units. This means that the animals should not even be aware they are being photographed as they pass by. The flash gives the animals’ eyes a ghostly glow when photographed at night.

• Track plates. These are square aluminum plates placed along game trails that are dusted with blue carpenter’s chalk. In the center of the plate is a sheet of sticky paper. Any animal that walks over the track plate leaves behind a blue footprint on the sticky paper.

Track plates are particularly useful in recording smaller animals, Perrine said.

• Bear collaring. The state Department of Fish and Game has captured two bears on the Cuesta Grade and fitted them with GPS collars. The collars allow biologists to track the exact movements of the bears in the area.

One of the bears still has its collar. The other was hit by a car. The collision was violent enough to knock the collar off the animal. It ran away, but biologists suspect it died soon thereafter.

Applying the findings

The most immediate application of the Cal Poly study will be in analyzing a Caltrans proposal to install another mile and a half of concrete barrier in the median of the highway at the top of the Grade.

These barriers are a common safety feature that prevents vehicles from crossing the median and hitting oncoming cars. The proposed barrier extension would go right through one of the most heavily used wildlife areas and could disrupt migration patterns.

Extending the concrete median would be done to prevent accidents, and the recommendation is based on a complicated formula taking into account traffic volume and highway width — not necessarily a history of accidents.

The Cal Poly study also comes at a time when bears are in the news. Fish and Game has proposed expanding bear hunting to San Luis Obispo County for the first time.

The department argues that the fact that so many bears are getting hit on the Cuesta Grade shows that the county’s bear population is robust enough to support a hunt and may even increase public safety. A decision on that proposal is expected April 21.

Reach David Sneed at 781-7930.