WILDLIFE CORRIDORS

The rapid expansion in urban areas throughout much of California is resulting in fragmentation of natural areas. Islands of natural areas that are too small for most large and medium sized species to survive in and are more vulnerable to competition from domestic cats and introduced urban species such as black and Norwegian rats. Introduced species have increased crowding of native species and altered the nature of ecosystems. Animals that require large habitat areas must be able to move from one isolated patch to another in order to find enough food resources and to limit inbreeding. To avoid the loss of wildlife, biologists have advocated the maintenance of “wildlife corridors” connecting isolated patches of natural habitat.

Examples of isolated area occur in our own area as urban development expands up the outlying canyon areas. Roadways tend to connect one canyon with another - thus creating barriers to movement. The several hundred-acre area now bisected by the Canyon Overlook Trail in Wood Ranch is an example. The area is completely isolated by housing and roadways. In order to move in and out of the area, larger species must cross roadways at the peril to life and limb. Coyotes, deer, raccoons and other animals are doing just that. However, they also tend to end up flat on the roads. Freeways, because of their size and chain link fencing, are nearly impassible.

Isolated pockets of natural areas are also impacted by domestic cats and dogs, which roam into those areas and pray on birds and rodents. The edge effect also works the other way in that coyotes, deer, bobcats, skunks, field and deer mice, and even mountain lions forage to one degree or another into the urban fringe. Those missing cats that are taken by coyotes and owls may have become victims by roaming into the wild areas or in their own back yards.

Little is known about the effectiveness of  wildlife corridors. One study suggests that most animals will not use small culverts under roadways. Many species are, however, known to use large culverts, such as the “wildlife corridor” under the freeway above Corriganville. Wildlife overpasses have been suggested for fostering movement in and out of the Santa Monica Mountains over the 101 Freeway. However, those studies that have examined this option have not been encouraging. Riparian corridors hold the most promise. However, those corridors tend to concentrate exotic species, such as cats, rats and house mice. So, without wide areas, riparian corridors have limited benefits. Hopefully, we will gain a greater understanding about what works and doesn’t - before it’s too late.

                                                                                    Mike Kuhn

12-7-04