Burrowing owls become more rare around the county

Article Date: 2010-11-07   Source: http://www.signonsandiego.com   Comments: 0

By Lily Leung

San Diego, California, U.S.A. - Burrowing owls in San Diego County - counted at 500 to 600 about 30 years ago - now number in the double digits at only a handful of sites.

Over the years, their continuing decline across California, the American West and Canada has been linked to the reduction of food sources, disappearance of habitat and deaths of burrowing mammals that historically have provided the owls shelter.

The burrowing owl's dire circumstances re-emerged this fall when scientists released new data showing a 27 percent decline in their population in the Imperial Valley, where 70 to 80 percent of burrowing owls found in California live. Less than 50 pairs of the owls now live in San Diego County, where their population has declined more than 90 percent.

The dwindling population could signal something is dangerously wrong with the ecosystem.

''Burrowing owls are like the miner's canary,'' said Jeff Lincer, research director of Wildlife Research Institute, a Ramona-based group that studies the burrowing owl.

Despite the dwindling population, conservationists and government agencies have recently reported pockets of good news - such as breeding activity at some sites as well as signs of use at artificial burrows.

The burrowing owl, unlike most owls, live and nest underground, usually in burrows dug by rodents. It is among the smallest of the owls, with a length of 8.5 to 11 inches.

Last week, two researchers with the California Department of Fish and Game visited 25 artificial burrows near the Sweetwater Reservoir maintained by two conservation agencies - to collect burrow data, from size to building material.

The researchers said they are attempting to create the first database of all artificial burrows in the San Diego region.

Fish and Game officials hope to collect enough meaningful data to determine the ideal nesting conditions of a burrowing owl, in an effort to promote breeding.

The information collected also will be used to update the California Natural Diversity Database, an inventory of the status and locations of rare plants and animals in the state.

Data collection played a key role in a recent study of the burrowing owl in the Imperial Valley, where most of them reside along irrigation drains and canals.

In that study, researchers counted 3,557 pairs in 2008, down from 4,879 pairs of in 2007.

Lincer said a 10 to 15 percent variation by year is expected, but ''we didn't imagine it to be that big.''

He added: ''It's certainly something we need to investigate.''

In the late 1970s and early 1980s, about 250 to 300 pairs of burrowing owls called San Diego County home.

The population began to drop as housing spread and more roads were built. The birds fell victim to passing cars. Many ended up living in irrigation canals in El Cajon.

In 2007, the number stood at only 46 pairs. The remaining owls live at the North Island Naval Air Station, the Ramona Grasslands, several areas in Otay Mesa and wildlife refuge lands.

The owls have largely disappeared from Los Angeles and Orange counties.

In recent years, biologists and conservation workers have seen glimmers of hope.

For example, Sweetwater Authority officials reported seeing burrowing owls attempting to breed last spring, a rare incident, said Pete Famolaro, the authority's watershed manager.

And on one occasion, they saw a ''plump California kingsnake'' in one of the artificial burrows, suggesting that there were eggs or young for the snake to chase after, Famolaro said.

''We've been able to recover a small population,'' he said. ''It's made a difference.''

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