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Burrowing owls are the only North American bird of prey that nests exclusively underground. (Steve Mandel)

The Little Owls That Live Underground

Burrowing owls can thrive amid agricultural development and urbanization—so why are they imperiled?

smithsonian.com

It’s almost midnight and a lone white pickup truck sits atop a grassy hill on a remote tract of government land near Dublin, California, that is used as a military training base. In the driver’s seat, biologist Jack Barclay hunkers down over a night-vision scope that amplifies light 30,000 times. Barclay is watching two quarter-size pieces of glowing reflective tape that mark a trap he has concealed in low weeds 100 yards away. He has brought a truckload of equipment to this site to band some of its few remaining burrowing owls.

Barclay sees a flicker of movement. Now. He presses a remote-control button, and a spring-loaded net arcs over the owl. Barclay sprints to the net and slips the owl headfirst into a plastic-coated can that once held frozen grape juice. The bird inside the can is still; only its legs protrude. Slits in the can’s side allow Barclay to examine the owl, and he records that this is a female. Under her breast feathers he sees a burgundy-colored “brood patch” of bare skin with abundant blood vessels that enables her to transmit heat efficiently to her eggs and young. Barclay attaches identifying bands to the owl’s legs and within minutes releases her.

Barclay began his career working with the Cornell Laboratory of Ornithology on an innovative program to reintroduce the peregrine falcon to the Eastern United States, from which the bird had disappeared. The reintroduction effort, which released captive-bred peregrines into the wild, was so successful that the program concluded its work in the mid-1980s.

Barclay eventually moved to California and joined an environmental consulting group. In 1989, he began monitoring birds at the San Jose International Airport, where a burrowing owl colony had set up housekeeping near the tarmac. The owls fascinated him and became his passion; he has devoted the past 20 years to working on burrowing owl conservation.

“I’ve always been interested in birds of prey,” he said. “Burrowing owls represent an interesting conservation challenge. It’s a high-profile bird that generates a lot of interest.”

Burrowing owls are playful, nine-inch-tall birds with bold, lemon-colored eyes. They are the only North American bird of prey that nests exclusively underground. Although they are called “burrowing” owls, the birds prefer to let other animals do the digging; they then show up as uninvited guests and appropriate the burrow. Because burrowing owls are active during the day, they are a highly visible species.

The owls often decorate their burrow entrances with dung, animal parts, bottle caps, aluminum foil and other trash. Scientists suspect the behavior may benefit the birds by attracting insects or signaling to other owls that the nest is occupied. During breeding season, a pale, sun-bleached male stands guard at a burrow entrance and brings food to the female, who attends to six or eight chicks in their underground sanctuary.

Strange as it seems, close-cropped fields near airport runways, like where Barclay first studied the birds, offer good burrowing owl habitat. The low-cut grass dotted with ground squirrel tunnels mimics the owl’s native rangelands that were kept short by grazing animals or prairie dogs.

In many places where burrowing owls could thrive, however, ground squirrels have been eradicated. Where this has happened, biologists sometimes install artificial burrows for the birds, often with volunteer assistance from an informal network of amateur burrowing owl enthusiasts. Barclay has published plans for an artificial burrow that is used in many locations. It is constructed from four-inch-wide flexible plastic piping that runs underground to a nest made from an irrigation valve box that’s roughly the size of a toaster oven. The bottomless molded-plastic valve box allows for a natural earthen floor, while the removable top provides easy access for biologists to monitor the birds.

In recent decades, as agricultural development and urbanization have spread across Western North America, the once-numerous burrowing owl has declined in vast areas of the Great Plains and Canada.

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