Conservation for the Birds—and Habitat

The Cactus Wren is the largest member of the wren family in North America.  As their name implies, they rely on cactus 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, 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.

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 wildland 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 biodiversity reserve and throughout San Pasqual Valley. In some areas natural recovery of the cactus has been suppressed by competition with exotic plants. As such, active restoration is needed to assist habitat recovery; however, little is known about the coastal cactus wren and its habitat needs or best practices for restoring cactus scrub habitat.

Therefore, researchers at the San Diego Zoo Institute for Conservation Research are working to restore 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.

This past year, Institute researchers have been busy restoring habitat and monitoring the cactus wren population on the reserve. In the winter, teams of volunteers helped to plant a total of 2250 cacti across 15 acres as part of the three year restoration phase of the project. Meanwhile, researchers carefully traversed cactus covered hillsides to complete a series of surveys that revealed a population of about 63 coastal cactus wrens living within the Safari Park’s reserve, confirming that the reserve is one of the last remaining strongholds for cactus wrens in San Diego County.

The Institute is also collaborating with USGS and the Nature Reserve of Orange County to color band and collect genetic material from the birds. The color bands will help researchers monitor the birds’ abundance, distribution and survivorship, and feathers collected during the banding will contribute to ongoing genetics research investigating the impacts of habitat fragmentation.  Furthermore, researchers are also working to set-up an acoustic monitoring program in which will contribute to a better understanding of the birds’ behavior. 

Several ongoing studies throughout southern California are focusing on habitat restoration and understanding population dynamics of the coastal cactus wren. Through the Coastal Cactus Wren Working Group, the Institute for Conservation Research is collaborating with the leaders of these projects to ensure the continued survival of cactus wrens in coastal southern California.