Friday, March 6, 2009
Midsized predators yield up their secrets to biologists.
By PAT BRENNAN
Orange County's bobcats prowl a knife's edge of life and death.
In a hopeful sign for the secretive felines, they appear to inhabit far more of the tiny, damaged fragments of habitat alongside urban enclaves than scientists previously thought.
But to get there, they cross busy streets that can become death traps – the cause of 26 out of 27 bobcat deaths in a 2 1/2-year period in central-coastal Orange County.
"From our mortality surveys, we found they overwhelmingly died by being hit on roads," said U.S. Geological Survey research ecologist Erin Boydston.
The eye-opening findings come in two hefty studies conducted by Boydston and other scientists over three years, both involving bobcat trapping, radio-collar tracking and monitoring with motion-triggered cameras.
"To me, they're right on this precipice in Southern California of maintaining these resident populations," said Colorado State University biologist Kevin Crooks, one of the studies' co-leaders. "But those populations are often isolated. I think it's fair to say they're in trouble, in some circumstances."
The second study tests the oft-repeated pledge by proponents of Irvine's "Great Park" – to create viable wildlife corridors through the property – and finds that it will likely be difficult, if not impossible, for the presently planned corridors to function properly without parallel efforts on adjoining properties.
The corridors would be unlikely to make solid enough links to surrounding wild areas to be useful to bobcats, a key predator, as well as other important species, Crooks said.
Blood, hair and feces samples revealed a more disturbing finding: cats heavily burdened with mange. A previous study by other scientists in the Santa Monica Mountains showed mange on bobcats could be related to consumption of rodents that have ingested chemical rodenticides. In the Great Park study, 10 bobcats were found dead of mange in inland Orange County.
"(A bobcat) euthanized by Animal Control was completely covered with mange, and emaciated," said Lisa Lyren, a USGS biologist and the lead author in the studies.
DNA from the blood samples also shows that bobcats in the interior of Orange County, near the Santa Ana Mountains, are genetically isolated from bobcats in the San Joaquin Hills, near Laguna Beach, likely because of the near impossibility of crossing 26 lanes of traffic at the El Toro Y, where interstates 5 and 405 meet.
A major reason for the studies was to find the corridors bobcats rely on, which could in turn help landowners avoid disrupting them with development and heavy human traffic. Bobcats are present in many wild areas in the San Joaquin Hills and around the Santa Ana Mountains, but the corridors are esssential: separated populations of animals and plants need naturalistic links between islands of habitat to keep up a healthy exchange of genes.
"Connectivity is the key to the persistence of carnivores in Southern California," Crooks said.
But for the bobcat groups separated by the two freeways, one of their only hopes is a long, dark tunnel beneath the interstates, at the El Toro Y, that few animals appear willing to enter.
"If we were going to look for a critical link for this, it would be that underpass," Lyren said.
Not only crossing through the intimidating tunnel, but navigating around homes and businesses on both sides would make the trip extremely difficult for bobcats and other wildlife.
"It's as if you're trying to get a pinball through a pinball machine," Boydston said.
Skylights within the tunnel, as well as thick vegetation cover at the two entrances, are among the measures landscape designers could take to make it more appealing to wildlife, the scientists said, though that was not a focus of their study.
A second passage beneath the 5 freeway appears possible for bobcats at Trabuco Creek, but the animals must travel much farther south to reach it.
Great Park officials would be willing to help pay for improvements outside their property to beef up the wildlife corridors, said Glen Worthington, manager of planning for the Great Park Corp.
"That would be our game plan," Worthington said – although they would likely seek funding partners, such as Caltrans.
He mentioned skylights, as well as a shelf inside the tunnel to allow animals to pass through without walking in mud, as two improvements that could make it a more viable corridor.
"We acknowledge that this is a problematic location," Worthington said. "We just think we can find a way to overcome that."
The genetics showed that somehow, a small number of bobcats occasionally make the journey from outside the San Joaquin Hills to mate within that largely isolated population.
But unless such links to wild areas outside the Great Park boundaries are improved, even a world-class wildlife corridor through the Great Park would be of little use.
"Without addressing all the constrictions along the biological corridor, the function of the entire linkage remains in jeopardy," Crooks said.
The $280,000 cost of the first study was paid for largely by the The Nature Conservancy, the second, at $100,000, mainly by the Great Park Corp. and the Irvine Co. Together, the studies paint a troubling picture of Orange County's bobcats, a favorite species for wildlife watchers and one that, unlike mountain lions, poses no threat to humans.
The radio collars relay bobcat locations using the global positioning system, and later drop off the animals automatically.
Plotting their day to day movements suggests they may be far more adaptable than the scientists had expected. But life in the forgotten pockets of wild habitat scattered along the urban edge is proving hazardous to their health – and, too often, fatal.
"Those seem to be supporting a few individual bobcats, and that is probably a good thing for the system overall – as long as the mortality is not so detrimental that it is driving the whole population down," Boydston said.
That mortality is most apparent on several roadway hot spots, where the scientists found high numbers of bobcat deaths – three or more during the study period. They include Newport Coast Drive in Newport Beach, University and Campus Drives in Irvine, and Alicia Parkway at Aliso Creek Road in Laguna Niguel.
The numbers from the studies are grim: necropsies, the equivalent of human autopsies, revealed that at least 26 of the 27 bobcats found dead during the 30 months of the first study were killed by cars. Of the five bobcat carcasses found during the 17 months of the second study, three had been killed by cars.
The researchers also trapped coyotes for tracking and analyzed coyote carcasses during the second study; all six coyotes found dead during the second study were killed by cars.
While the numbers are telling, they are not a perfect measure of causes of death; Boydston cautions that animals killed by cars are more likely to be found by people than those that die for other reasons. Still, they show the hazards the animals face in an urban setting.
The Santiago Fire of 2007 swept through the area during the second study, and at least one bobcat – one not collared in the study – was found dead of injuries suffered in the fire.
The death illustrates another problem for the cats, Boydston says. Wildfire can push surviving bobcats into areas of poor habitat, or to places where they are more likely to be struck by cars.
"These other kinds of events come in, and that's when the life and death balance becomes even more critical," Boydston said.
It's too late for mountain lions in the San Joaquin Hills, now considered "functionally extinct" there, though a population remains in the Santa Ana Mountains. But it might still be possible to create viable wildlife corridors for bobcats and other predators from the mountains to the ocean.
Crook's colleague at Colorado State, Jeff Tracey, used the research to develop a computer model of bobcat movement that could help land managers: plug in a few perameters, run the model, and see if you've created a working wildlife corridor.
They hope their work will help others find ways to preserve top predators wherever they survive, including mountain lions, bobcats, coyotes and gray foxes.
"It still impresses me, amazes me, that we can still retain this suite of carnivores, ranging from small to large, in coastal Southern California," Crooks said.
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