On Road to Hoover Dam, bighorns get a bypass

This was on AZCENTRAL.com today, written by Shaun McKinnon of the AZ Republic,
"Along the final few miles of U.S. 93 in northwestern Arizona, as the highway approaches the new Hoover Dam bypass bridge, three smaller concrete spans cross the freshly repaved traffic lanes.
The overpasses are not for vehicles or pedestrians, at least not the two-legged kind. They were built by the state for wildlife, specifically the desert bighorn sheep that roam the rough-hewn Black Mountains.
Ceremony for Hoover Dam bypass bridge
State officials know critics may question the need to build bridges for wildlife or object to the cost, $4.8 million for the three structures. But the two state agencies behind what is thought to be a first-of-its-kind project say the overpasses will help preserve Arizona's largest herd of bighorn sheep and improve highway safety by steering the animals away from traffic.
"You get only one shot at this," said Bob Posey, supervisor for the Kingman office of the Arizona Game and Fish Department. "If, 10 years from now, we saw problems, there'd be nothing left to do but watch. This was an opportunity to make a bad situation better."
The bad situation wasn't all new. U.S. 93 was built decades ago, carrying traffic across Hoover Dam between Arizona and Nevada. The highway cut through the middle of bighorn sheep habitat and isolated the only real water source, the Colorado River, on one side.
The Black Mountains are home to about one-third of Arizona's desert bighorn sheep. Rams from the herd have been transplanted in other parts of Arizona, Utah, Colorado and Texas.
Biologists knew some of the sheep crossed the two-lane highway, 15 harrowing miles of sharp turns and steep inclines, but some sheep stopped and turned around. The fragmented habitat made it difficult for the sheep herd to recover from drought or disease and to breed properly.
"Movement is critical for bighorn sheep," said Zen Mocarski, education manager for the Game and Fish Kingman region. "As we cut animal populations into smaller and smaller segments, we start to see inbreeding. . . . It's not a good thing to have happen."
Losing genetic diversity in a species can hasten its decline. The sheep are important to Arizona's landscape not only for their value as an iconic native species and as popular game animals, but also for their role in maintaining a diverse ecosystem.
A long drought had already contributed to losses in the Black Mountain herd, which shrank from about 1,800 sheep to about 500 in the early part of the last decade. So when the Arizona Department of Transportation decided to widen U.S. 93 to four lanes and add medians and fencing as part of the bigger bypass-bridge project, wildlife officials became involved.
The project initially called for wildlife underpasses, which have been built for deer and elk in other parts of the state, but the Game and Fish Department wasn't sure that was the right option for bighorn sheep.
"Bighorn sheep are very visual," Mocarski said. "They can see movement up to a mile away. Their eyesight is one of their primary defenses, so asking them to go underground, in a dark and dank tunnel, might not work."
Biologists decided to ask the sheep. Working with sportsmen's groups, the agency captured and collared 75 bighorn sheep in areas along U.S. 93 and Arizona 68, the highway between Kingman and Bullhead City.
Underpasses had been built on Arizona 68, so the study enabled the state to collect two kinds of information: Where sheep crossed the highway and whether they used the underpasses.
The underpasses were not popular. And the sheep definitely had strong preferences about where they wanted to cross, locations longtime hunters knew about.
"The sheep have crossed the road at the same several places for as long as I've been out there," said Curt Steinke, vice president of the Arizona Desert Bighorn Sheep Society, a group of sportsmen long active in sheep conservation.
"They want to look down on things," Steinke said. "They're happy when they can see things from above."
The group contributed $60,000 toward the tracking collars and put up more money to help the state monitor the sheep.
With more than 100,000 data points from the collared sheep, the Game and Fish Department and ADOT found three locations, one 12.2 miles from the dam, the second 5.2 miles from the dam and the third 3.3 miles from the dam.
ADOT added the overpasses into the design of the expanded highway. Federal highway money paid 95 percent of the construction costs, both of the overpasses and of the full $71.3 million widening project, ADOT officials said.
The sheep bridges look much like any highway overpass: built of concrete and anchored to ridgelines on each side of the highway. But the surfaces are dirt and have been seeded with native plants. They are not accessible from the highway or from any developed trails.
Mocarski said he knows some people will ask why the government went to so much expense for a few hundred sheep.
"We've already interfered with them," he said. "We've built roads and fences, we drive cars. Now the goal is to manage wildlife."
The question now is whether the sheep will use the overpasses and begin to move more freely across their range.
"Nobody's really ever tried it before, not an overhead bridge," Steinke said.
The overpasses were finished in late January, and fences were removed. On Feb. 1, remote cameras attached to the overpasses snapped the first photographs of sheep crossing the highway.

Read more: http://www.azcentral.com/news/articles/2011/02/21/20110221hoover-dam-bridge-bypass-bighorn-sheep.html#ixzz1Ee55wers