Data show thousands of animals using RTA wildlife crossings

This year, cameras on the State Route 77 wildlife crossings north of Tucson have observed two milestones for the first time in the five-year duration of the overpass and underpass structures: a white-tailed deer crossing the overpass in January and a first crossing of either structure by a mountain lion in June.

Those were notable, unique sightings. Otherwise, mule deer, javelina, coyote and bobcat make up 98% of the crossings at the overpass and underpass, totaling nearly 15,000 documented crossings in five years.

When the Regional Transportation Authority formed and its Citizens Advisory Committee evaluated potential categories to direct funding, the CAC considered a request from the Coalition for Sonoran Desert Protection to spend some of the sales tax collections to construct wildlife crossings. The 20-year, voter-approved RTA plan includes funding for wildlife crossings to reduce vehicle-wildlife collisions and provide connectivity between large blocks of open space.

Representatives of the RTA’s Wildlife Linkages Committee, which included a coalition member, worked with the Arizona Game and Fish Department to evaluate the wildlife connections between the Tortolita and the Santa Catalina mountain ranges, and to plan one of the biggest urban wildlife crossing projects in the state: the underpass and overpass to allow large and small wildlife species to cross Oracle Road, or State Route 77.

The RTA spent $11 million on the overpass, underpass and fencing to direct animals to the safe crossing sites when the Arizona Department of Transportation widened the busy road from four lanes to six lanes in 2016.

“The RTA opened up a lot of opportunities for wildlife crossings,” because it provided a funding source, said Jeff Gagnon, statewide connectivity biologist for the Arizona Game and Fish Department.

AGFD has monitored the Oracle crossings sites with cameras ever since they opened for use and has observed steady or increasing use by the four most commonly detected large species at the crossings, according to regular reports on the data gathered from the cameras.

Mule deer prefer the overpass and have steadily increased their usage of it every year, while more coyotes and javelinas have used the underpass. Bobcats use both without a strong preference, and all four species have been documented by trail cameras using both types of crossings. The trail cameras at this site are set to detect these larger animals, though smaller species do show up on camera occasionally.

“We’re interested in everything we detect,” said Colin Beach, AGFD senior research biologist.

The department monitors other crossings throughout the state, and some are more heavily used. But the RTA project in southern Arizona continues to provide learning opportunities.

“This is kind of new for us, in particular, in that this is a fairly urban setting we’re working in,” Beach said.

The animals that are used to urban areas, “they’re not as skittish, they just tend to use something that you wouldn’t normally think they would use as much,” Gagnon said. “They’re not scared, because they’re around people so much,” compared to animals that do not live in an urban wildlife interface.

Nearby to the west, almost 10,000 animals have used the five wildlife underpasses along Tangerine Road since they were constructed with RTA funding as part of the Tangerine widening project in 2018.

The five underpasses entail varying designs and sizes, and because they have a lower height clearance, the size of a drainage culvert rather than a large underpass, the trail cameras are placed closer to the ground and can pick up images of large and smaller animals.

Together with the Oracle crossing sites, the Tangerine crossings help animals in the Tortolita to Catalina corridor area safely cross the roads, which are otherwise dangerous barriers to migration.

“Things like a mountain lion, which have very low population densities, they need to be able to traverse these large distances,” Beach said. “In order for those populations, as a whole, to persist, they need to be connected. They need to be able to cross highways and pass through urban areas. We know they move around in those areas, but it’s valuable to be able to actually document that connectivity.”

Gagnon said there is a learning curve for the animals.

“It’ll take time for them to learn it and then, once they learn, you start to see them bringing their young through, and I think it just kind of carries forward from there as they learn to use it as part of their movement range. They can now utilize it, and once they learn how to use it, they’ll continue to use it for as long as it’s there.”