Researchers, trackers study deer populations
LOS PENASQUITOS CANYON —— For a decade, governments throughout San Diego County have bought into the idea that wildlife and development could coexist, if enough open space was preserved with corridors built between them to allow animals to roam.
Local governments used the theory when federal environmental laws required them to develop so-called habitat conservation plans.
The plans identify which land can be developed and which should be preserved so native plants and animals can survive and, perhaps, thrive.
The question is, does it work?
Researchers from San Diego State University and a group of animal trackers, many of them from North County, have teamed up to find out.
On the front lines of the research are Southern mule deer, the only large plant-eaters native to San Diego County. Their droppings, called scat, can be collected so researchers can extract genetic information to figure out where individual deer have been living and whether they use the corridors that connect larger swaths of open space.
The corridors are important, scientists say, to provide wildlife with enough room to roam in their quest for food and mates. If deer use the corridors, researchers figure, so will other wildlife.
"Much of the time, it's not so easy to find where deer have been," said naturalist Karen Larsen-Gordon, a member of the San Diego Tracking Team that is working on the project. "We look either for tracks or for browse, signs that animals have been eating."
Finding fresh scat
Larsen-Gordon and a partner waded through a field of waist-high dry grass in Los Penasquitos Canyon last week, quickly finding signs of deer. In the middle of an area of flattened grass the size of a couch, Anna Gateley-Stanton bent down and examined her prize —— pellets of deer scat.
"It's hard to find the fresh stuff," she said. "It can't be more than 48 hours old."
Gateley-Stanton slipped on green latex gloves and scooped the pellets into a plastic box. Larsen-Gordon recorded the exact location of the find, using coordinates from a Global Positioning System radio.
The San Diego Tracking Team is a nonprofit organization that trains volunteer trackers to survey wildlife. Together with ecologists at San Diego State University, they are studying the size and health of deer populations around North County.
Andrew Bohonak, an assistant professor of biology at San Diego State, says the technique of collecting genetic material from scat allows researchers to follow individual deer around the county's open spaces without touching or even seeing them.
As humans continue to build roads, homes and shopping centers on what was open space, San Diego governments have designed wildlife corridors that sometimes include tunnels to pass under busy highways that would otherwise present a danger to animals trying to cross them.
Biologists have been studying the tunnels in Southern California for the last decade, trying to figure out the optimum size, design and location for them.
For example, a dump-truck-sized tunnel under Interstate 5 that was designed to connect Torrey Pines State Preserve with Los Penasquitos Canyon Preserve to the east, turns out to be too forbidding for deer, especially with recent construction nearby, according to Bohonak's studies.
As a result, a small population of around 20 deer living at Torrey Pines is trapped there, according to genetic analysis performed by Bohonak and former graduate student Shea Valero, now a wildlife biologist for the U.S. Department of Agriculture. The situation can lead to inbreeding, making the deer susceptible to disease and other problems.
A nonfunctional corridor
Valero and Bohonak recently submitted their results to the research journal Conservation Genetics. The paper describes three choke points or bottlenecks that seemed to constrain the movement of wildlife between open space areas. The choke points are :
- The underpass near the merge of Interstate 5 and 805, south of Del Mar;
- A fence-lined corridor across Highway 94 in southern San Diego County;
- An underpass under Highway 52 near Mission Trails Regional Park.
Deer are not passing through the I-5/805 underpass, although they are moving along the other two corridors, the researchers found.
Their findings contrast with an earlier study from 2001 by Valero and fellow graduate student Sierra Hayden, which identified tracks of deer, bobcats and coyotes around the 5/805 underpass.
"It shows that all the construction around the freeway since then has made that corridor nonfunctional," Valero said.
Although the deer at Torrey Pines don't move east, they're genetically similar to the deer living 15 miles away, near Mission Trails Park. That hints that in the past, Torrey Pines deer might have migrated southeast, perhaps through Marine Corps Air Station Miramar land, she suggested.
After testing the DNA techniques on a small scale, Bohonak is scaling up by collaborating with the tracking team. Together, they'll collect deer scat samples at 14 different locations, from Torrey Pines to Sycamore Canyon in Poway.
"I've been working on the molecular biology techniques for a while, but the tracking team is in a unique situation," Bohonak said. "They know more than almost anybody else about tracking wildlife in Southern California."
The tracking team was founded by airline pilot Barry Martin. After working in Los Penasquitos Canyon for a decade, the team is beginning to spread its efforts throughout the county.
Duane Boney, a team member and Escondido city park ranger, has worked with five volunteers to monitor wildlife at the city's Daley Ranch open space preserve for the last year.
"We've got a core group of people that are pretty gung-ho, but we'd like to get some more," he said. "Not all of us are natural scientists, but we all like being detectives."
Boney said he's eager to begin looking for tracks around and within three 15-foot-high wildlife tunnels that were recently installed under Valley Center Road.
The land east of Daley Ranch used to be a thoroughfare for wildlife, according to Boney. But increasing traffic on Valley Center Road has cut off Daley Ranch from large areas of open space to the east. Five mountain lions crossing the road were killed by cars in the 1990s, he said.
The county's recent $50 million project to widen Valley Center Road has blocked animals from moving between Daley Ranch and the undeveloped land around Valley Center to the east, Boney said.
Individuals and groups
The genetic scat tests have their limitations. The San Diego State's genetic studies only look at deer, so information on other species is incomplete.
In contrast, direct observation —— using infrared cameras or looking at animal tracks around and inside wildlife corridors —— could identify several kinds of animals at once.
Where the genetic studies have an advantage is that they can identify individual animals and determine how they are related to each other, Valero said.
"You can fit the two kinds of studies together and really get the best of both worlds," she said.
A very direct way to monitor deer would be to put radio-transmitter collars on individual animals —— a technique that UC Davis researchers have been using on mountain lions in Cuyamaca Rancho State Park for the last four years. Cost and manpower is a problem, however. Each collar costs $5,000 and putting one on an animal requires a team to capture and sedate it, Valero said.
"The important thing about the scat (genetic) studies is that they're not invasive," she said.
For information about the San Diego Tracking Team, visit http://www.sdtt.org/.
Contact staff writer Quinn Eastman at (760) 740-5412 or firstname.lastname@example.org .