Concrete and Asphalt ‘Cages’



Living in Southern California can be problematic with crowded conditions, urban sprawl and nightmarish traffic. These challenges present a double and triple whammy to urban wildlife that must navigate, circumvent and survive in a landscapethat wasn’t here 50 years ago.

Discussing how “Urbanization Isolated Wildlife” on June 18 at 2 p.m. at the National Park Service Visitor Center in Thousand Oaks will be Dr. Katy Semple Delaney, an ecologist who has recently published a study on this phenomenon.

Delaney has focused her attention on the genetic makeup of four specific animals in small scrubland patches and parks surrounding Thousand Oaks and State Route 23 – an area that was pretty much large swaths of wilderness in the 1960s.

Delaney, along with folks from the U.S. Geological Survey, examined and compared the DNA of three common lizards – the Western fence, side blotched and Western skink – as well as a small songbird, the wrentit.

                              WRENTIT — PHOTO BY TOM GREY — USED WITH PERMISSION

Delaney says she chose non-endangered species because she wanted to see the effects of urbanization on commonly-found animals – critters that are surviving well in the big scheme of things. These animals also represent different ecological niches and range of mobility. For example, Western skinks tend to be secretive debris dwellers, while Western fence lizards are fast-running, more mobile animals.

“We looked at little habitat islands that were isolated from each other by houses, roads and development,” Delaney says about this 10 mile area that has seen, throughout the decades, enormous changes from a rural countryside to heavily people-populated.

Delaney discovered that urbanization brought two important aspects to surface: first, animals get “stuck” in an area, unable to move beyond the preset boundaries. (She may call it “stuck,” but we’re going to call it “in the jailhouse.”)

“We found this true especially with the lizards, but it was surprising that the bird also stayed in its habitat island,” she says, offering a possible explanation as the small wrentit isn’t a big-winged flyer.

The second finding is that in these isolated patches, animals tend to be closely related to one another. Inbreeding. That terror word for biologists everywhere. “Even if there are patches of the same animal not that far away, there is not a lot of migration back and forth,” says Delaney.

And who can blame ‘em? What animal wants to brave a freeway with big monster metal vehicles? What animal wants to cross over backyards with high fences not to mention cats, dogs and kids with sticks? Asphalt parking lots, concrete walls, brick buildings – not exactly high on the skink’s list of travel stops on its way to visit relatives on the other side of the shopping center.

So, with their natural habitats fragmented, animals are staying put, breeding with each other, and in some cases, according to Delaney, going “extinct” on those habitat islands. “Some populations of fence lizards have just disappeared from certain areas,” she says.


If you remember your Darwin, you know that when animals inbreed, they lose their genetic diversity which, in turn, raises the bar of extinction down the road. Mixing the pot is always good.

While Delaney expected to find such patterns in her study, she was stunned by the speed of evolution. “To see this kind of change on a small scale – really about 50 generation – was surprising,” she says. “It’s happening faster than we thought.”

Armed with this research, Delaney hopes to expand her reach to include other critters – maybe more specialized species in the area like bobcats and coyotes – to see how these animals are dealing with urban barriers that, in a sense, cage them.

From a practical point of view, what can developers, government officials, urban architects and the like take from this study? “There needs to be ways for animals to cross roads safely, corridors that connect populations together,” she says. She points to the successful European greenway system, green spaces that connect natural areas, which allows animals a way to safely cross the road.

After all, if a chicken can safely cross a road, why can’t a Western skink?

Find out more details about Delaney’s upcoming discussion here.

— Brenda Rees