Saving the Coastal Cactus Wren
It is a beautiful cool morning and the gibbons have been singing melodically since sunrise. As I climb onto up onto a rocky outcrop to get a better view of my surroundings, I hear the roar of a lion in the distance. Far below, I can see a herd of antelope grazing on the fresh green grass and a couple of giraffes casually browsing on acacia leaves. Behind me, I hear the sound that I had been hoping for – the rhythmic sewing-machine like song of a California coastal cactus wren.
I grab my binoculars and turn to find that he is only about 80 feet away, perched atop a cactus and singing emphatically to declare his territory. The colored bands on his legs indicate that he was one the nestlings that we banded last spring –now a mature adult with his own territory. His mate is nearby with a wad of dry grasses in her beak, which she proceeds to tuck into a large football-shaped nest protected by spiny prickly pear pads.
When people think of wildlife conservation, images of gibbons or giraffes often come to mind–exotic animals in remote areas of faraway lands. Many people are surprised to discover that there are species in their own backyard that are in trouble. My work with the San Diego Zoo Institute for Conservation Research is focused on saving a songbird that lives literally in the backyard of the San Diego Zoo Safari Park in Escondido, California: the California coastal cactus wren.
The 800-acre biodiversity reserve located on the cactus-covered hillsides overlooking the Safari Park hosts one of the last robust populations of these troubled wrens. The coastal cactus wren is in trouble because the type of habitat that it needs–cactus dominated coastal sage scrub–is rapidly disappearing. This habitat once was found throughout coastal southern California but is now confined to small isolated patches, like the one at the Safari Park. Urbanization, frequent fires, and the introduction of invasive species have each done their part to reduce the amount of quality habitat available to wrens and other native wildlife.
Since habitat loss is the primary cause of its decline, saving this little bird involves saving its habitat. To do so, I and others from the Applied Plant Ecology Division have joined forces with the Animal Ecology Division to determine what exactly the wrens need and the best way of getting it to them. Our goal is to restore cactus in areas of San Pasqual Valley where recent wildfires have taken a toll. Cactus restoration is a long and prickly process.
Each year, we arm ourselves with thick PVC coated gloves and harvest thousands of cactus pads by prying them from mature adult cacti using barbecue tongs. We use these harvested cuttings to grow more cacti. In the winter, we don our thick gloves, hiking boots and rain gear and begin the long process of transporting the cacti out to the sites that we have selected for restoration and planting them in the ground. Each year, we plant 2,250 cacti over 15 acres in order to achieve our goal of restoring 45 acres over the course of 3 years. While hiking up the same hill for the 5th time with an armful of cactus seems tedious, I know that it will be worth it - especially when I hear a cactus wren calling in the distance and imagine that its offspring may one day make that hill their home.
Cactus tends to be a very slow growing plant, so in our planting fury we are experimenting with ways to help the cactus get established and grow faster. The sooner the cactus patches reach the critical height of 3 feet that the wrens need to nest, the better for the population.
Some of the methods that we are testing include surrounding individual cacti with wire cages to prevent herbivores like wood rats from eating them, head starting the cacti in a nursery so that they develop a nice root system before planting them in the field, and hand watering them during summer to encourage faster growth. Each cactus is marked with an individual ID tag and we conduct surveys twice a year to track their health and survival. Coming up with creative ways to encourage growth and seeing how they work out over time is one of my favorite parts if the job.
What I love most about habitat restoration is that you can see the change that you are making. Year by year I can see changes in vegetation taking place as the cacti that I propagated and planted grow taller and begin to fill in the gaps where exotic annual grasses once grew. But I know that the most exciting part is yet to come – a few years from now, I hope to see a pair of coastal cactus wrens building a nest within the protective arms of a large restored cactus patch overlooking the Safari Park’s large field enclosures.
Sara Motheral, Research Technician, Applied Plant Ecology, San Diego Zoo Institute for Conservation Research.