Volunteers and Refuge Staff install burrowing owl boxes. Boxes were buried leaving only the entrance tunnel and a vertical pipe out the nest's top visible. The pipe allows biologists to examine the nest's condition with a flexible camera. Photo by Earl S. Cryer and used with permission.

Recontoured pools hold the winter rainfall and provide habitat for vernal pool species such as the endangered San Diego fairy shrimp. Photo by John Martin, SDNWR Biologist.

A burrowing owl enjoys the view from the entrance to its new nest box on San Diego NWR. Photo by Earl S. Cryer and used with permission.

Jill Terp, San Diego NWR

Can you spot them?  You’ll need to look carefully to find these very small ground-dwelling owls.  With mottled brown and white feathers, burrowing owls (Athene cunicularia) – only 19-25 centimeters tall – are nearly invisible in their grassy or bare soil habitat.  The burrowing owl is also difficult to find because it is becoming rare in San Diego County due to loss or conversion of its habitat. 

The Friends of the San Diego National Wildlife Refuges partnered with refuge staff, Sweetwater Authority, and volunteers to improve habitat for burrowing owls.  One year ago for National Public Lands Day on September 29, 2007, ten artificial burrows were installed for the owls’ use on the San Diego National Wildlife Refuge near the Sweetwater Reservoir.  Until recently, the area where the burrows were installed was overgrown with non-native grasses.  With funding from the San Diego Association of Governments, habitat restoration started with removal of several tons of grass thatch that revealed clay soils typical of vernal pools.  The landscape was then sculptured to restore the shallow pools that had been degraded by past farming.

Vernal pools are small ephemeral wetlands that retain water on a seasonal basis.  Vernal means “spring” and these pools typically fill with our late winter or spring rains.  Despite being ephemeral (the pools dry out and remain dry for much of the year) they provide habitat for many rare plants and animals including the endangered San Diego fairy shrimp (Branchinecta sandiegonensis). 

In addition to vernal pools, there are plenty of places for that are high and dry for owl burrows.  Burrowing owls usually rely on colonies of California ground squirrels (Spermophilus beecheyi) since the owls don’t dig their own their burrows.  Burrows are used for nesting, resting, and protection from predators.

As a bird of prey, the burrowing owl catches small rodents and large insects but will also catch reptiles and amphibians.  To find enough prey, the owl requires large areas of open space adjacent or very near the nest burrow.  They spend much of their time close to the nest burrow, but will travel much further to find adequate food for themselves and young.  Burrowing owls hunt by day and night and are most active in the morning and evening.  They catch more insects during the day and more mammals at night. 

The burrow installation goes hand-in-hand with similar restoration taking place on adjacent Sweetwater Authority lands.  There, habitat restoration and placement of burrows has resulted in burrowing owls moving in within a week!  And we had the same success!  Owls were seen using the burrows only 8 days after installation. 

In January 2008, refuge staff worked with the Chula Vista Nature Center and Sweetwater Authority to release some owls that had been born in captivity.  The Nature Center had a female burrowing owl that was captured after she repeatedly preyed on endangered California least terns (Sterna antillarum browni); she was placed on exhibit with a non-releasable male.  Her male exhibit mate is an older bird that suffered a foot injury, which left his toes clenched into a fist.  Staff never intended to have them breed and didn’t think the male would be able to; however, in 2007 nature and the birds' breeding instinct prevailed.  The pair produced five chicks while residing on exhibit. 

Those chicks, now grown, were banded so they could be identified at a distance and placed in a special cage at the vernal pool restoration area.  Called a hack cage, this enclosure helped the owls acclimate to their new surroundings, with hope of improving their chance for survival and increase the odds of having them stay in the area.  The owls were fed and monitored by the Nature Center Bird Crew. At the end of five days, the enclosure was removed and the owls had their first taste of freedom.

After release, biologists John Martin of the San Diego National Wildlife Refuge and Peter Famolaro of Sweetwater Authority monitored the owls.  At least eight owls were detected in September 2008 at the site.  Several of the owls have not cooperated enough to allow checking for leg bands but two captive-bred birds have been seen along with newly fledged young of the wild owls! 

As open space becomes scarcer, habitat restoration and conservation will play an increasingly important role in the survival of animals like the burrowing owl.  Everyone involved in this project hopes that the habitat will someday be home to an even more thriving burrowing owl population in San Diego County.