BY Karyl Carmignani
The tiny data-collecting backpacks on the burrowing owls have to weigh less than five percent of the bird’s body weight to not impinge on its activities.
Night owl by day
Its watchful, unwavering gaze scans the landscape from atop a fence post. Long, thin legs support a dappled tan and white body and swiveling head. Small for an owl, this bird is just shy of a ruler in height. The researcher’s binoculars meet the bird’s laser-focused, golden eyes beneath downy white “eyebrow” feathers. Its curved beak is ready for action. A tiny rustle in the brush prompts the bird to spring from the post and silently glide just above the ground, talons spread. In an instant, the burrowing owl is swiftly airborne, clutching a stunned, soon-to-be-eaten grasshopper. Nearby, four fluffy owlets milling outside a burrow entrance await their next meal.
San Diego Zoo Global is committed to leading the fight against extinction for species around the globe and close to home. The western burrowing owl Athene cunicularia hypugaea of Southern California has been on a collision course with development for decades, with its open grassland habitat coming under siege, as well as ground squirrel control programs significantly reducing burrow availability. The San Diego Zoo Institute for Conservation Research and the U.S. Fish and Wildlife Service (USFWS) are collaborating on a project to improve mitigation strategies for this ground-dwelling, diurnal species.
It’s a multi-pronged, multiple-partner, team effort to better understand the ecology of these birds and to test new strategies to improve the overall efficacy of active and passive relocation protocols for burrowing owls. In recent years, “It has become rather bleak for burrowing owls, with all the development in San Diego County,” said Lisa Nordstrom, Ph.D., associate director of Recovery Ecology at the Institute. “We are hoping to turn around the trajectory for this endearing species.”
A few decades ago, horseback riders in rural San Diego County would inadvertently flush out scores of burrowing owls, which would take to the air in harried haste. These days, this pint-sized raptor is a California Species of Special Concern, a designation to ensure specific conservation protections to reduce further population declines. While there is no halting development, a goal of this project is to collect data on two different translocation methods used in mitigation strategies: passive (the default method used in California), where an excluder door is placed at the burrow entrance, keeping the birds out and “forcing” them to relocate, sometimes to specific areas equipped with artificial burrows; and active translocation, where the birds are collected and physically moved to a safe area, and kept in a temporary field enclosure for one month prior to release (see field enclosure photo above).
However, there is uncertainty about the effectiveness of either of these methods, due to lack of data. This study will compare outcomes for the owls using both methods, as well as a control group. “This program will generate comparative data that people who work with this species have been wanting,” explained Colleen Wisinski, conservation program specialist at the Institute. “Wildlife agencies need these scientific data to better conserve the burrowing owl.”
The program covers a wide range of burrowing owl habitats across four counties in Southern California (Riverside, San Bernardino, Imperial, and San Diego), and while many of the owls breed here, their movements can be unpredictable. To collect robust data, the team is planning to catch and track more than 60 burrowing owls. Using solar-powered satellite GPS telemetry in the form of tiny, lightweight backpacks on the owls, researchers will gather waypoints from the birds every two to four hours and track relocated owls in their new digs, observing movement patterns, breeding success, and survival rates.
Catching the owls can be challenging, but using a tasty mouse as bait or vocal call/playback methods will usually entice them. Each burrowing owl gets a U.S. Geological Survey (USGS) band with a number (like a Social Security number), as well as a colorful alphanumeric “name” that researchers can read with binoculars and a camera. Blood and feather samples are collected, and our Genetics team at the Institute carries out testing to tease out which owls are related. The birds are handled for as short a time as possible (less than 30 minutes) to minimize stress on the animal. Monitoring methods include strategically placed trail cameras, burrow scopes to observe burrow chambers, and researchers observing them with binoculars and spotting scopes.
Burrowing owls are one of the smallest owl species in the world.
Signs and Signals
For translocated animals, “settling” in the new area is critical for reducing mortality rates. “Conspecific cues will signal to other owls that the habitat can support them,” said Sarah Hennessy, postdoctoral associate at the Institute. “We will use visual and auditory cues near the artificial burrows” so the new birds will stick around. Simulated whitewash made with nontoxic white paint in a syringe, squirted around a burrow entrance, resembles natural burrowing owl poop, which other owls will find reassuring. “If there’s a lot of poop around the burrow, owls flying by can see it from the air and know the area is suitable habitat,” she added.
Acoustic playbacks of prerecorded burrowing owl vocalizations will also be used to reassure newcomers that the area is owl-friendly. “These birds are semi-colonial and more likely to live in groups than singly,” said Colleen. This biologically relevant mixture of calls will help to build up a colony of translocated burrowing owls.
When burrowing owls are alarmed, they make a hissing call that sounds like a rattlesnake.
Currently, relocations depend on the installation of artificial burrows, and much work has been done designing the best artificial burrows for the owls. Wooden burrows (as opposed to plastic) have a better microclimate (temperature and humidity) in the chamber. “Artificial burrows are a short-term management tool,” explained Lisa. “Burrows created by squirrels and other animals are the long-term tool.” Researchers will also collect founder birds this year to begin conservation breeding at the Safari Park. This will allow us to produce birds for release into San Diego County to establish new breeding nodes, to dodge local extinction. San Diego Zoo Global is committed to better science, better conservation, and better economic outcomes for this endearing local species. “We are using everything we have learned over the last eight years to maximize success of this conservation program,” said Sarah. It’s something we can accomplish with a little help from our friends.
San Diego Zoo Global would like to thank its valuable partners and supporters: United States Fish and Wildlife Service, San Diego Foundation, California Department of Fish and Wildlife, County of San Diego, City of San Diego (Airports and Public Utilities Divisions), California Department of Transporation, San Diego State University, San Diego Association of Governments, California Energy Commission, Western Riverside County Regional Conservation Authority, Imperial Valley Community Foundation, Imperial Irrigation District, Coachella Valley Conservation Commission, and 29 Palms Band of Mission Indians.
Photos by (from top): SDZG (2); Ron Swaisgood; SDZG; Jacob Hargis; SDZG; Colleen Wisinski; Ron Swaisgood; Colleen Wisinski; Michael Stevens.