Creatures that find such culverts are the lucky ones. Out here, cars have been transformed into predators, and carnage is everywhere. According to a painstaking, eight-year study by Saguaro National Park, up to 53,000 vertebrates are killed annually on roads either flanking or dissecting Saguaro's east- and west-side units. This staggering death toll has also made Saguaro the poster child for parks coping with urban sprawl on their doorsteps. "Our issue will be every park's issue in 10 years or so," says Kline. "It's a huge problem."
Saguaro is currently revising its general management plan, and that update is expected to include several strategies for reducing roadkill. They range from erecting roadside barriers and reducing traffic speeds to borrowing from the culvert idea and creating animal passageways beneath the roads. That's why Kline is pleased to find animals are traversing these twin tunnels. "Obviously, not everybody can use them, because they're small," she says, squatting down to inspect a pile of scat. "But something like a badger or a fox sure could."
By turn, if traditional culverts are transformed into something bigger and more naturalistic, more animals will likely use them. And that could help reduce the staggering number of creatures killed on roads around Saguaro. At the same time, methods proving successful here may also be helpful in other parks around the country, where urban sprawl is increasingly reaching preserve boundaries. The nation has about 4 million miles of public roadways, and roughly 10 percent of those roads touch on public lands such as national parks. Each year, those roadways are responsible for at least 1 million animal deaths.
It's a grisly situation--more so the closer you get. When Saguaro's roadkill study began, a single surveyor cruised 47 miles of road weekly. But a big part of the picture was still missing, says Kline. "When you're driving, you just don't see everything. We realized our weekly survey, which was supposed to represent a week's worth of roadkill, didn't do so for a million different reasons. Animals are taken off the road, sometimes by scavengers, sometimes by people. Sometimes, they are washed off the road, or squished into oblivion."
But even those beefed-up numbers didn't tell the whole story. Just as important, says Kline, is knowing which species are dying. "Lots of cottontail rabbits and Gambel's quail are killed on the roads. While that's sad--and certainly not something we want happening in the park--it's not going to affect populations, because those creatures are used to high mortality rates."
But other species populations "are very susceptible to roadkill," she says, "(like) rare animals and those such as desert tortoises and Gila monsters that don't reproduce as quickly. If they live to adulthood, they're expected to be reproductive for a long time. So when you get indiscriminate mortality like roadkill, and you start taking adults out of the population, you can impact their populations very quickly."
After documenting the problem's enormity, next comes doing something about it. "The first step is understanding where the wildlife passages and corridors are," says Alison Berry, director of the Road Ecology Center, at the University of California at Davis. "Where do they migrate from, and where are they going to? It's important to understand the ecology of the animals. Then you can go on to (developing) structural barriers, various kinds of underpasses or culverts, and wildlife crossing structures."
These increasingly sophisticated approaches have even gone high-tech, such as wide, vegetated overpasses where cameras monitor animal use. In fact, the whole science of "road ecology" is growing exponentially around the country, and cutting-edge techniques are discussed at yearly symposiums, such as the International Conference on Ecology and Transportation.
Arizona is among these leading innovators. For example, when a highway in central Arizona was widened from two to four lanes, state Game and Fish Department biologists helped design a series of wildlife passages. Elk were a particular concern in the area, and several were fitted with radio collars to track their movements through those passages. In Southern Arizona, the Coalition for Sonoran Desert Protection wants to increase funding for wildlife underpasses and other "critical landscape linkages" in the proposed Pima County transportation plan. While the plan already includes $25 million for such linkages, the coalition argues that at least $45 million is necessary for adequate wildlife protection.
Certainly, these projects don't come cheap. A huge culvert was recently built under Sandario Road at Saguaro west, and fitted to encourage wildlife traffic. Saguaro scientists conducted an environmental impact study for the project; the final price tag was a cool $1 million, which was split between Pima County and the Federal Highway Administration. But for Natasha Kline, that cooperation highlights the public commitment needed to preserve Saguaro and its inhabitants. "It takes a village to preserve a park," she says. "I really believe that."
Now she glances at Picture Rocks traffic, dusting hands on her hips. "Our mandate is to preserve and protect the natural and cultural resources of Saguaro National Park," she says, "so they can be enjoyed by future generations. But that mandate can be tough. The very means of providing access to those resources often directly conflicts with preserving and protecting them."
Kline pauses as another car rumbles by. "Roads," she says, "are a perfect example of that."