Wrens and Restoration
The cactus wren is the largest member of the wren family in North America. As their name implies, they rely on cactus—especially prickly pear and cholla—for nesting, foraging, and protection.
Unlike most other birds, cactus wrens use nests year round for roosting (sleeping); they build a covered, football-shaped nest with grasses and other vegetation. If you are lucky enough to live in an area with cactus wrens, you might hear their strident song that sounds like a sewing machine.
Cactus wrens are fairly common in the desert, however, here in Southern California they are declining because they rely on a very unique and rare habitat—cactus scrub. There are several small populations of coastal cactus wren in San Diego, Orange, Riverside, Los Angeles, and Ventura Counties, but they are becoming more and more isolated from each other because of urbanization and habitat loss.
In urban areas, they face an array of predators that they wouldn’t normally have to deal with—especially domestic cats. Cats are very able predators and birds are one of their favorite treats.
Population isolation can be a problem because of decreased genetic diversity, which can lead to decreased disease resistance, problems caused by inbreeding, and increased susceptibility to catastrophic events (like wild fires). Basically, all of a species’ eggs end up in just a few baskets—no pun intended.
In 2007, the Witch Creek Fire damaged much of the cactus scrub habitat at the Safari Park’s 900-acre native species reserve and throughout San Pasqual Valley. Natural recovery of cactus scrub habitat has been very slow, and in some areas recovery is further suppressed by the invasion of exotic grasses and wild mustard which compete with native plants. Because of limited recovery, tall cacti are not abundant and are required by coastal cactus wren for nesting.
Active restoration is needed to assist habitat recovery for the coastal cactus wren; however, little is known about the coastal cactus wren and its habitat needs or best practices for restoring cactus scrub habitat. Therefore, we will be restoring 45 acres of cactus scrub habitat in an experimental framework, while monitoring cactus wren abundance, distribution, survivorship, and productivity over the next five years to investigate cactus wren habitat requirements and their response to restoration.
Not only are we studying coastal cactus wrens at the Safari Park, but there are several ongoing studies throughout Southern California focusing on habitat restoration and understanding population dynamics. Through the Coastal Cactus Wren Working Group we are collaborating with the leaders of these projects to ensure the continued survival of cactus wrens in coastal southern California.