Awestruck, wildlife ecologist Robert Burton surveys a maze of tunnels and underground chambers that was once the burrow of an endangered giant kangaroo rat.
Such a burrow can be up to 7 feet deep and cover an area of 30 square feet. Biologists call these intricate underground labyrinths precincts. They are used by the small rodents to escape predators, store food and avoid the scorching summer heat of the Carrizo Plain.
“They’re absolutely amazing,” Burton said. “We didn’t know they could be so elaborate. Kangaroo rats have probably been using this precinct for decades.”
The burrow was excavated by workers at the California Valley Solar Ranch, a 250-megawatt photovoltaic plant under construction north of the Carrizo Plain National Monument. Any kangaroo rats found in the burrow were captured and relocated to new, artificial dens nearby.
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In what the U.S. Fish and Wildlife Service says is an excellent cooperative effort, Burton and his team will relocate as many as 304 giant kangaroo rats in order to make way for installation of new solar panels.
The work will also shed new light on the ecology of the endangered rodents and could be used as a template for solar plants proposed to be built in areas that also have giant kangaroo rats, such as the Panoche Valley in San Benito County.
“One of the great successes so far in this project is the private/public partnership that has made this conservation effort successful,” said Robert Moler, spokesman for the Fish and Wildlife Service in Sacramento. “This partnership effort is a great example of how energy companies can work with the USFWS for future solar projects.”
As its name implies, the giant kangaroo rat is the largest of some 20 kangaroo rat species found in the American Southwest. They hop using a long tufted tail and powerful hind legs. Adult rats can reach lengths of about 7 inches and weigh 7 ounces.
They are endangered because only about 2 percent of their grassland habitat remains and is fragmented. SunPower will conserve 12,000 acres in and around its solar plant to be used as endangered species habitat.
The process of relocating kangaroo rats begins when biologists survey an area where solar panels are slated to be installed for evidence of active burrows. On the surface, a burrow is just a small cluster of vertical and horizontal holes, belying the complex underground structure beneath.
Once a burrow is located, as many of the rats as possible are captured using small baited box traps.
Some of the animals avoid these devices, so after about six days of trapping, workers begin slowly and carefully dismantling the burrow.
Any rat remaining in the burrow eventually breaks cover as the diggers approach and tries to hop away. Biologists capture them by hand, implant an identification chip and collect a tuft of fur for later genetic testing.
“They’re pretty docile once they’ve been caught,” Burton said.
Within about 15 minutes, the rat is placed in a new artificial burrow nearby. The new den consists of a buried box with two cardboard tubes that slant up to the surface of the ground.
Five pounds of feed — enough to last the rat about six months — is also included. All of this is surrounded by a mesh enclosure, the sides of which extend about a foot underground.
The idea is to force the rat to dig new tunnels to escape the enclosure. This sizable expenditure of time and effort coupled with the food cache will likely make the rat adopt the enclosure as its new burrow rather than try to return to its old den.
The effort appears to be successful, said Brian Boroski, vice president of H.T. Harvey & Associates, the Fresno-based ecological consulting firm conducting the capture and relocation program.
Of the 217 giant kangaroo rats relocated so far,
only 31 have gone missing from their new burrows. These missing animals could have fallen prey to predators or taken up residence in a different burrow, Boroski said.
The first rats were relocated in September 2011, and new burrows have already been established near the artificial ones. These were likely built by the offspring of the first relocated animals. Rats have also established new burrows beneath the newly installed solar panels.
Biologists hope to limit the number of rats relocated to 250, well below the 304 animals allowed under the company’s federal permit. This was accomplished by carefully locating solar panel arrays, roads and other disturbances away from rat burrows, Boroski said.
The California Valley Solar Ranch is one of two large commercial solar plants under construction in California Valley. It is already producing 22 megawatts of power, and that output should rise to 130 megawatts by the end of the year, said Ingrid Ekstrom, SunPower spokeswoman. Construction is scheduled to be complete by the end of 2013.
The other solar plant is the 550-megawatt Topaz Solar Farm. It is expected to begin feeding power into the electrical grid early next year and will finish construction in early 2015.
When both plants were proposed in 2008, it was clear that endangered species would be the main environmental concern. The Carrizo Plain contains some of the last grassland habitat in the state and has one of the highest concentrations of endangered species in California.
San Joaquin kit foxes are the main concern with the Topaz plant. Operators there have a plan to conserve that endangered species. The plan consists mostly of making the plant friendly for kit foxes but not coyotes, their main predator.
The California Valley plant also has four kit foxes. SunPower has a conservation plan for them, as well, Moler said.
“We have seen no project-related kit fox injuries or fatalities,” he said. “We have seen many of the species occupying and raising young within the onsite conservation lands in close proximity to the project.”
But giant kangaroo rats are far and away the main challenge at the SunPower plant. Boroski has some 40 wildlife biologists, including Burton, working on various aspects of the project.
Under the plant’s first design, about 90 percent of the kangaroo rats living in the 1,500-acre footprint would have been impacted. Over the years, the layout received four major revisions and multiple smaller redesigns. The layout that received final county approval in April 2011 avoids 90 percent of the kangaroo rat precincts.
The amount the company is paying for its mitigation work is not available.