Years of research, planning, and development showed early signs
of success when video and still photographs captured two rams
crossing the recently completed wildlife overpasses near the Hoover
It marks a small, but significantly meaningful achievement that
Arizona Game and Fish Department and Arizona Department of
Transportation (ADOT) officials hope will minimize the impacts of
desert bighorn sheep fragmentation through the Black Mountains and
improve traffic safety.
The overpasses are the result of years of collaboration between
ADOT, Game and Fish, the Federal Highway Administration, the
National Park Service, and the Arizona Desert Bighorn Sheep
Society. They are part of a construction project which widened an
existing 15-mile section of US 93 south of the Hoover Dam from a
two-lane road to a four-lane divided highway. The project was
completed before Thanksgiving.
When word arrived almost a decade ago of the planned widening of
Highway 93 and the Hoover Dam Bypass effort, Game and Fish
personnel pondered the fate of bighorn sheep throughout the
The Black Mountains bighorn sheep herd holds the largest contiguous
desert bighorn population in the nation and has supported
transplants to help restore historical populations in Arizona,
Utah, Colorado, and Texas.
Fragmentation and habitat loss remain the leading cause of wildlife
extinction. A four-lane highway in this area was going to increase
the “barrier effect” for bighorn sheep, making it even more
difficult for them to cross safely from one side of the highway to
the other and raising concerns about the long-term sustainability
of the herd.
“There was no question we had to move quickly,” said Bob Posey,
supervisor for the Game and Fish office in Kingman. “We had to
explore the options and build on the knowledge and relationships
we’d gained through our previous coordination with ADOT and Federal
Highways on the highly successful Highway 260 project east of
With several underpasses already planned for wildlife, the problem
wasn’t just whether the crossings would be in the right locations;
it was whether those underpasses would be used by bighorn
Federal Highways provided Game and Fish with the necessary funding
to conduct research near the Hoover Dam and along Highway 68 (from
Kingman to Bullhead City), where several underpasses were already
The results along Highway 68 were surprising.
“What we discovered was that while many bighorn sheep approached
the underpasses, few actually used them to cross,” Posey said. “It
was time to think like a bighorn. It became clear these animals
wanted to remain high, and crossing under a road wasn’t their
“Bighorn sheep prefer to remain above potential dangers. Crossing
under a roadway is avoided by bighorns because it is a great
location for predatory animals.”
The study on Highway 93 not only provided information on where the
bighorns preferred to cross, it concluded they approached the
highway from ridgelines.
When presented with the information, which included approximately
100,000 data points, plans to develop underpasses were scrapped in
favor of three well-designed overpasses with fencing essentially
‘funneling’ sheep to the crossings.
“With current technology, our confidence and scientific predictions
are more effective,” Posey said. “The bighorn sheep themselves
provided all the information. This is wildlife conservation-based
science at its best.
“ADOT strives to have the least possible impact on the environment
when it is building or improving a highway,” said ADOT Public
Information Officer Michele Beggs. “We are very pleased to see the
first photos and video images of the Desert Bighorn Sheep using the
wildlife overpasses, which were built to provide a safe crossing
for the sheep and to protect motorists traveling this busy stretch
ADOT has dedicated nearly half a billion dollars to widening and
improving US 93 from Wickenburg in Maricopa County to Hoover Dam
over the last several years.
“Our long-term vision is to transform this highly traveled route
into a four-lane divided highway through the entire 200-mile
stretch,” said Beggs. “The US 93 series of projects is a priority
for ADOT and has become a significant addition to our state highway
system to more efficiently move people, goods and services.”
The three bridges cost just under $2 million each, and Posey
believes it’s money well spent.
“This was a fantastic collaboration between agencies,” said Posey.
“You get only one shot at this. If, 10 years from now we saw
problems affecting this herd, there’d be nothing left to do but
watch. This was an opportunity to make a bad situation
The research effort took place in three stages: the first to study
movements and underpass use before construction, the second to
study bighorn interaction as construction took place, and the
third, which is currently taking place, will study the
effectiveness of the overpasses.
“This is historic,” Posey said. “As far as I know, these are the
first overpasses built specifically for desert bighorn sheep in the
nation. While animals such as deer and elk will use
well-constructed underpasses, more visual animals, like bighorn
sheep and pronghorn, are more hesitant.
“It’s not enough to just put these overpasses in place. We need to
know how well they work,” Posey added.
While the first two sheep captured on the bridge is reason for
optimism, the overall success of the project will be told over
For more information on the Highway 93 project, visit
www.azgfd.gov/w_c/research_maintain_sheep.shtml (link to the video
is in the right-hand column) or