FARMINGTON, Utah (AP) — Crews replacing power poles in a great blue heron rookery at a Utah nature center have made a surprise discovery: a nesting box with three barn owl chicks and three eggs.

The crews' work will be halted until at least October when the owls mature enough to be on their own, said Diana Vos, director of the Great Salt Lake Nature Center at Farmington Bay.

Any further disturbances to the nesting box in the interim could deter the mother from returning, Vos told the Deseret News (http://bit.ly/U1Xy8l).

Rocky Mountain Power crews hauled in six 40-foot poles for installation in the rookery this week after a December windstorm toppled several nesting platforms for the great blue heron.

But the project, designed to replace the toppled platforms and provide sturdier poles for the herons, was abruptly halted after the unexpected discovery of the barn owl chicks.

"What a surprise," Vos said. "We have a nursery, and we couldn't keep doing our stuff."

Inside the nesting box, she said, were "three little heads of barn owls that popped up."

"They can't be more than a few days old," she said.

The new poles and nesting platforms are designed to accommodate the groups of great blue heron that will build nests beginning in February and stay to raise their young.

Standing more than 4 feet tall with wing spans of 6 feet, the giant birds have become a popular attraction at the center.

The nature center is on the extreme edge of the Farmington Bay Waterfowl Management Area, which hosts 60 bird species that build nests there each year. More than 200 species of birds can be spotted at the bay, and some 5 million birds make a stop annually.

The appearance of the barn owl chicks so late in the season is unusual, Vos said.

"It is possible for owls to have more than one brood again in a season but not typical," she said.

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Information from: Deseret News, http://www.deseretnews.com