Widlife Corridor

Planners consider animal movements in road plans
Oracle Road could get wildlife underpass


By: Ty Bowers
March 26, 2008


She says conservationists and highway engineers use the “same words, but with different meanings.”

When talking about corridors and linkages, for example, engineers think of moving people from Point A to Point B, said Siobhan Nordhaugen, a special projects consultant with the Arizona Department of Transportation.

Conservationists use those terms when discussing ways to keep animals moving throughout their ranges.

At an Oro Valley forum last Thursday, Nordhaugen sought to draw that contrast as she spelled out an ADOT study’s findings on wildlife corridors throughout Arizona. The agency plans to take animals’ needs into accounts as it makes plans to build and expand roadways in the future.

That new concept of transportation planning drew the interest of 100 or so Oro Valley residents concerned about balancing the concerns of humans and wildlife, especially as the town begins annexation talks with the state about Arroyo Grande, a 14-mile stretch of undeveloped desert crucial to animal movements between the Santa Catalina and Tortolita mountains.

ADOT’s plans to widen a 4.4-mile stretch of North Oracle Road, from Calle Concordia to Tangerine Road, to six lanes will probably include an animal underpass of sorts, according to Nordhaugen.

Preliminary plans show construction of a 12-foot-tall, 32-foot-wide passage beneath Oracle, linking Catalina State Park with Big Wash. The 190-foot-long passage should allow animals to move safely from one mountain range to the next, Nordhaugen explained.

Conservationists hope the state agency builds more underpasses along Oracle Road, said Carolyn Campbell, executive director of the Coalition for Sonoran Desert Protection.

Campbell’s group, which sponsored the Oro Valley forum, has concerns with the way Arroyo Grande may be developed. To Campbell and others, the area is priceless, not in terms of real estate value, but in terms of its importance to many animal species.

Mule deer forage in the Catalina and Tortolita foothills, often crossing a busy Oracle Road. Other animals, from small to large, also cross the multi-lane highway.

It’s this “fragmentation” that worries biologist Trevor Hare, of the Tucson-based Sky Island Alliance. The group seeks to preserve animal movements in the network of mountain ranges in Southern Arizona.

“We know that fragmentation is the main threat to species’ biodiversity,” Hare said.

When hemmed in by development, members of a species can die out as inter-breeding and competition for limited resources increase.

Throughout the state, ADOT has begun researching ways to limit such fragmentation as well as animals’ and humans’ often-fatal encounters on roads. Though only one-third of the solution, road placement and engineering have become key tools to preserving some of the state’s more sensitive species, according to Ray Schweinsburg, a research manager for the Arizona Game and Fish Department.

Animals don’t cross roads willy-nilly, Schweinsburg said. They do so at predictable points. It requires extensive study to determine exactly where.

Schweinsburg pointed to ADOT’s construction of two elk underpasses along Route 260 near Payson. After studying where elk crossed, he explained, ADOT then built a series of fences designed to “funnel” the massive animals into the underpasses and safely across the road.

In 2004, before the fencing and underpasses were installed, 51 collisions of elk between vehicles occurred, according to Schweinsburg. The next year saw only eight wrecks.

“We know we need fencing,” he added. Otherwise, animals have no way of knowing such underpasses were designed specifically for them.

Of course, Schweinsburg noted, not all species use the crossings in the same way, or at all.

Whether the proposed ADOT animal underpass on Oracle will work remains uncertain.

Hundreds of mule deer, for example, likely move between the Catalinas and Tortolitas, according to scientists. Throughout the Tucson region, mule deer numbers remain low. Game and Fish Department helicopter surveys in 2003 and 2004 found 2,621 mule deer, numbers well below the five-year average of 3,263 in such surveys.

Game officials blamed the decline then on drought and development.

Also, scientists know that mountain lions frequently cross Oracle Road. One University of Arizona study of mountain lions in 2004 and 2005 tracked a radio-collared male on a 400-square-mile trek around the Catalinas and Tortolitas.

“We need to document where these corridors occur,” said Acasia Berry, acting director of the Sky Island Alliance. “We certainly know that the Northwest is where a lot of these linkages are threatened.”

Development of Arroyo Grande will only heighten scientists’ concerns about wildlife connectivity, Berry said. Proposed underpasses and other engineered fixes can do but so much, she added.

“None of these solutions are ideal. They’re not solutions. They’re mitigation.”