Burrowing owls get new homes after sprawl pushed them out - The San Diego Union-Tribune
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After sprawl drove them away, San Diego burrowing owls get new homes at Ramona Grasslands

 Christina Schaefer and Trish Jones Mondero inspect the entrance of an artificial burrow for owls in the Ramona Grasslands
Christina Schaefer and Trish Jones Mondero inspect an entrance to an artificial burrow that leads to a nesting box for owls at the Ecological Preserve at the Ramona Grasslands on Nov. 12.
(Nelvin C. Cepeda/The San Diego Union-Tribune)
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Small rare owls are getting a new home on the Ramona Grasslands Preserve, after decades of urban sprawl nearly eliminated them from San Diego County.

Last winter the San Diego Habitat Conservancy introduced 24 burrowing owls to their new digs on the preserve through a reintroduction project with the San Diego Zoo Institute for Conservation Research and state and federal resource agencies.

The breeding pairs honeymooned in artificial burrows, and guarded over clutches of eggs until the chicks hatched, adding the next generation of owls to an area where they had all but disappeared.

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In January biologists will transfer several more pairs in hopes of expanding the population of the little, long-legged owls.

“The chicks that are born here hopefully will come back to breed,” said Christina Schaefer, a private biologist and conservancy board member, standing beside a man-made burrow on the sunny plain.

The Ramona grasslands are the second site in San Diego County slated for burrowing owl reintroduction. In 2020 researchers released eight young owls to Rancho Jamul Ecological Reserve in hopes of expanding a fledgling colony there.

With brindled, brown and cream fur and round, lemon-yellow eyes, burrowing owls are small in size, around seven to 10 inches tall.

They need short, open grassland to hunt for prey — mostly insects, small lizards or rodents — and to hide from predators such as coyotes or great-horned owls.

Western burrowing owl
Western burrowing owls, keeping an eye, or two eyes, on things.
(San Diego Zoo Global.)

They also require grasslands for shelter. Burrowing owls are the only North American owl species to nest underground and make their homes in tunnels dug by ground squirrels.

“They use the California ground squirrel as their ecosystem engineers,” Schaefer said. “Ground squirrels dig the burrows, and the owls move into them.”

Over the years, however, people have been exterminating squirrels as pests, leaving fewer to dig new burrows. Meanwhile housing construction and other development has consumed much of the flat, open real estate the owls prefer.

Two years ago zoo researchers said there were only about 75 breeding pairs left in the county. Schaefer said they’re so rare it’s hard to tell how many remain.

The Ramona Grasslands County Preserve is the largest remaining expanse of open, grassy plains in San Diego County. The 3,521-acre preserve is sort of a living library of biodiversity with vanishing habitat types, including grasslands, wetlands, vernal pools, coastal sage scrub and oak woodlands. It hosts hundreds of unique plants and wildlife, ranging from ephemeral fairy shrimp and endangered arroyo toads to bald eagles and hawks.

“We’re trying to conserve and preserve and manage these high-quality lands,” said Don Scoles, executive director of the San Diego Habitat Conservancy, a nationally accredited land trust that acquires and protects land and manages 31 open-space preserves in the county.

Within the Ramona Grasslands is a 210-acre mitigation bank, where developers can buy credits to compensate for projects that affect protected habitat. This is where the burrowing owls are settling in.

To get started, the conservancy had to identify the right land, with grassy habitat and appropriate soil for burrows, and without nearby perches for larger owls and other predators.

A young long legged burrowing owl that was being release in to the wild on to the Rancho Jamul Ecological Reserve o
A young long legged burrowing owl that was being release in to the wild on to the Rancho Jamul Ecological Reserve on Wednesday, January 29, 2020.
(John Gibbins/John Gibbins)

The grasslands evolved with native grazing animals, including deer and pronghorn antelope, so the land managers mimic that by selectively grazing the site with cattle. This keeps grasses short enough for the owls to find prey and avoid predators.

Although the grassy plain is pocked by rodent holes, researchers constructed artificial tunnels and nest chambers for the breeding birds. Each burrow hosts one pair and consists of two reinforced entrances leading to a plywood box buried underground.

Researchers will place the breeding pair in a burrow and cover it with a portable aviary, a wire mesh enclosure that temporarily keeps the owls in place for several weeks until they reproduce. Once they have a clutch of eggs, researchers can remove the aviary and the owls will stay put of their own accord until the chicks are fledged, Schaefer said.

Weighted buckets cover holes above the nest chambers. While the pair are brooding and rearing chicks, researchers can lift the buckets to check on the young owl families and deliver frozen mice to feed the new parents.

Getting the pair comfortable in their new home is an easy sell, when you consider that the alternative is a smaller rodent hole, Schaefer said.

“They love the artificial burrows,” Schaefer said. “They prefer those over squirrel burrows. Because who doesn’t like a villa over a cabin?”

 in Ramona, CA., Christina Schaefer and Don Scoles from a distance scout out their next burrowing owl nesting site
At Ecological Preserve at the Ramona Grasslands on Friday, Nov. 12, 2021 in Ramona, CA., Christina Schaefer and Don Scoles from a distance scout out their next burrowing owl nesting site to inspect.
(Nelvin C. Cepeda/The San Diego Union-Tribune)

The birds are social creatures, so researchers play recordings of burrowing owl calls to help them feel at home until the colony becomes established.

There are about five owls living at the site now; the rest of the transplants migrated after breeding. Researchers hope that some of last winter’s chicks will return to start their own families at their birthplace. When the owls begin using the site for multiple generations, researchers will know the reintroduction efforts are working.

“What makes it successful is not that we relocated them, but that they breed and return to the area they’re from” Schaefer said. “Burrowing owls have a very strong homing instinct.”

Researchers hope not only to maintain but also to enrich the grasslands, helping reestablish some of what has disappeared from San Diego’s natural environment.

“Our goal is to preserve what we have so we don’t lose it,” said Trish Jones Mondero, a spokeswoman for the project. “But we also want to expand the biodiversity. We want to make sure we have higher biodiversity in 20 years.”

Although burrowing owls require extensive care during the reintroduction process, that’s intended to be temporary. Subsequent generations will have to locate burrows, seek mates and feed themselves during the breeding period. Biologists hope the population will grow naturally and expand to adjacent areas.

“Eventually we go away, and they do this all on their own,” Schaefer said.

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