More about Burrowing Owls

The fence around the Burrowing Owl area in the northeast corner of the park is back up, more or less, and the preserve is ready for its unique feathered guests to come spend the winter.  It has the required features:  plenty of ground squirrel burrows that the owls take over as their homes, rocks to perch on or hide under, and fair amounts of small dry and wet critters for them to eat. But how many Burrowing Owls will come, if any at all, is anyone’s guess.  The trend line isn’t encouraging.  Between 2007 and 2013, the number of visiting owls hovered between three and six.  In 2014 and in early 2015 there were only two.

Their slow decline in this preserve mirrors their statewide retreat in most areas, according to a bird research anthology, “Proceedings of the California Burrowing Owl Symposium,” published in 2007.  Twenty scholarly papers record the immense patience of bird observers up and down the state who spent countless hours looking for Athene cunicularia hypugaea and recording their findings.  On the whole, not good.  These birds nest in the ground, a highly vulnerable location, where loose dogs, cats, raccoons, skunks, cattle, ATVs and human boots can put an end to them.  They rely almost entirely on ground squirrels to dig their nesting holes; where humans undertake campaigns to exterminate ground squirrels, the owls are in trouble.  They also like flat, grassy or bare terrain near water at low elevations, precisely the kind of terrain where developers like to put condos and subdivisions.  Most of the land where owls live is privately owned. Bottom line: the owls are in trouble.

Paradoxically, some kinds of human development make the owls happy.  The largest thriving populations of Burrowing Owls in California today are in the Imperial Valley, on the border with Mexico.  Industrial agriculture turned this desert into an artificially irrigated greenbelt with miles of canals threaded through laser-straight vegetable fields.  Here, along the irrigation canals, the Burrowing Owls flourish like nowhere else in California.  They spend all day in the fields cleaning them of small rodents, lizards, and other little creepy and crawly things.  They’re exposed to high levels of pesticides, but so far without apparent harm. The authors of the monograph estimate that between fifty and seventy per cent of all the Burrowing Owls in California today live in this narrow region.

In the San Francisco Bay Area, these birds were once abundant but at the time of the published surveys there were no more breeding pairs in San Francisco, Napa, Marin, and Santa Cruz counties (only the occasional winter visitor).  Susan Townsend and Colleen Lenihan, authors of a monograph on the Burrowing Owl in the San Francisco Bay Area written in 2003, estimate that breeding pairs are probably gone from southwest Solano and San Mateo counties, and may be disappearing entirely from western Contra Costa, western Alameda, and Santa Clara counties.  The only sites where abundant breeding pairs have been seen are in eastern Alameda and eastern Contra Costa counties, particularly in the Altamont Hills and the Altamont Pass.  However, the development of wind turbine arrays and related ground disturbances and rodent extermination efforts underline the fragility of these owl populations.  Established owl populations were also noted at the San Jose airport and at the NASA Ames Research Center.  The authors report that several mitigation efforts, such as efforts to evict breeding pairs from one tract of land and move them to another, have shown very low success rates, in part because the birds demonstrate high site fidelity and in part because the relocation efforts have been mishandled.

Very little is known and very little is being done by way of mitigation for loss of Burrowing Owl habitat statewide, report Edward Stanton and Sherry Teresa in their contribution to the volume.  Only two sites in California are mandated to maintain owl populations.  One of them is the Dublin Ranch Preserve, and it is very small; at the time of the monograph, a management plan for this land was still being developed.  What is known, the authors write, is that preservation of the ground squirrel population is basic for Burrowing Owl habitat.  Thus, measures that help the ground squirrels, such as excess vegetation removal, also help the birds.  Beyond that, not much is really known.

Removal of Burrowing Owls to allow construction of a golf course in eastern Alameda County is the topic of a monograph by Judy Bendix.  The site contained about eight thousand ground squirrel burrows. Teams of workers installed thousands of simple one-way traps which would allow owls and California Tiger Salamanders (which also inhabit ground squirrel burrows) to exit but not to re-enter.  This effort, Bendix reports, was very expensive.  It did eventually succeed in clearing the area of nesting pairs during golf course construction, and at least some of the displaced birds took up residence nearby.  After the golf course was operational, however, ground squirrels returned and dug burrows on irrigated greens, and some pairs of Burrowing Owls made their nests and successfully raised fledglings on the golf course.  That’s site fidelity.  The monograph does not discuss what if any measures were taken to avoid disturbance of the birds by golf course users and staff.

Another case study reports on Burrowing Owl mitigation efforts at the San Jose airport.  To reduce the risk of collisions between aircraft and birds, airport staff closed off natural (squirrel-made) burrows near runways and installed artificial burrows made of concrete blocks and plastic pipes in less hazardous areas of the airport’s terrain.  A few Burrowing Owls re-excavated closed-off burrows or even dug new burrows without squirrels present, but the artificial burrows proved, on the whole, hugely popular.  The breeding population increased from ten pairs in 1990 to forty pairs in 2002, and nearly three fourths of these pairs in 2002 occupied the man-made burrows.  Still, the birds were choosy; some artificial burrows were occupied for a dozen years, others have been shunned.  No one knows why.  The author cites the airport’s management plan as a success story for Burrowing Owl stewardship.

A less happy story comes from Colonel Allensworth State Historic Park  in Tulare County.  Reconstruction of historic buildings and crowds drawn by special events required efforts to move the existing Burrowing Owl colonies to less disturbed nearby terrain.  Artificial burrows were installed.  However, due to flawed management, inadequate staffing, and inability to control hazards such as packs of off-leash dogs from nearby residences, the owl population declined and, at the time of writing, showed no signs of recovery.

The Burrowing Owl is listed as a Species of Special Concern by the California Department of Fish and Game.  This is a lower classification than endangered species status, but it does point to the need for a statewide conservation strategy.  So say Esther Burkett and Brenda Johnson in their contribution to the volume.  They point to a wide range of stakeholders and a broad array of measures that must be taken for monitoring and managing the birds’ status so as to prevent their further decline statewide.  A petition to list the Burrowing Owl as an endangered or threatened species under the California Endangered Species Act (CESA) was filed in 2003; it eloquently details range contraction and habitat losses.  The petition has been without result so far.  The birds are listed as Endangered in Canada and Threatened in Mexico.

The book concludes with a bibliography containing 230 published sources about the Burrowing Owl.

This scholarly monograph was illuminating about the Big Picture of the birds’ history and about the public policy issues that surround them and largely determine their fate.  But it offers little by way of up-close observation of these charming and beloved creatures.  For that, we can go to other sources on the web.  Just pop “athene cunicularia hypugaea” into Google, or click on this link, to get links to thousands of web sites, images, and other publications on these fascinating birds.

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