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MANDATORY CREDIT A burrowing owl is seen on the Highway 4-Lone Tree Way construction jobsite near Cavallo Road. (Copyright California Department of Transportation)

ANTIOCH -- A tiny burrowing owl family that threatened big delays for the near half-billion dollar Highway 4 widening project has flown safely out of harm's way.

While working near a new overpass at Cavallo Road this summer, contractors with Bay Cities/Myers discovered that a family of burrowing owls -- mother, father and three owlets -- had made a nest in a burrow near a freeway retaining wall.

The family of raptors left the embankment in late September and the burrows have since been removed, Contra Costa Transportation Authority officials said this week.

"I think it was a happy ending," said Ivy Morrison, an authority spokeswoman. Officials followed "passive relocation" protocols set by the state Department of Fish and Wildlife and California Burrowing Owl Consortium to relocate the owls, she said.

Their presence did not slow down Highway 4 construction, though some work scheduling had to be shuffled.

"Luckily, we were able to follow all the correct procedures and it worked out fine," said Oakley Mayor Kevin Romick, vice chairman of the authority board.

The presence of owls at that location was a bit peculiar, but not a huge surprise.

"Those things happens every time you engage nature," Romick said. "You have to be aware of who might be present and how to work around if you encroach."

When the owls were first spotted, a buffer zone of 250 feet -- marked in spots with temporary orange-colored fencing -- was established around the nest to keep machinery and contractors away.

The burrowing owl's nesting season is from Feb. 1 to Aug. 31, but only after the birds have fully fledged can the buffer zone be removed.

Morrison explained that a field biologist conducted pre-dawn surveys to determine which holes in the area the owls were living in. Around early September, the biologist observed the three owlets had fledged and were seen "flying and hunting," she said.

"That established that they were self-sufficient and could manage on their own," Morrison said.

One-way flap doors were installed on the holes so the owls could safety get out of the burrows, but not back in. A telescoping camera was also used to confirm the holes were empty before they were excavated by hand, Morrison said.

Standing about 10 inches tall and weighing less than a pound, burrowing owls are identified on Fish and Wildlife's list of species of special concern, meaning their numbers are shrinking. One place where they are abundant, though, is in East Contra Costa's grassy hills.

Officials are already using the episode as a learning experience for next year.

Starting in January, Morrison says the biologist will continue doing pre-dawn surveys along the corridor and plug any mammal burrows.

"We're trying to be a little proactive, and discourage them from nesting near an active construction site," Morrison said. "It certainly raised everybody's awareness."

Contact Paul Burgarino at 925-779-7164. Follow him at Twitter.com/paulburgarino.