VACAVILLE (CBS13) — Much-needed infrastructure repairs in Vacaville are up in the air over concerns about a threatened bird.

“These bridges were built back in the 50’s,” said Caltrans spokesman Vince Jacala. “It’s something that we have to update and take care of.”

The Midway and Meridian bridges, which cross Interstate 80 just east of Vacaville were scheduled to be updated together this week. The plan was to demolish the Midway overpass and construct a new one that met modern seismic standards. Then do the same for the Meridian bridge.

“We had to shift our construction focus,” said Jacala. “Our construction focus right now is to work on the Meridian Bridge instead of the Midway Bridge.”

The change is because biologists made a discovery. A Swainson’s Hawk is nesting in the trees next to the Midway Bridge.

“Caltrans can’t do any work within 600 feet of their nest,” said Jacala.

“Everybody that builds in California and the Central Valley knows the rules of the game,” said Judith Lamare, the president of the Friends of the Swainson’s Hawk.

The birds have been on the state’s threatened list since the 1980s and are protected.

“Historically there were about 17,000 Swainson’s hawks. Today, there are about 4,000 breeding Swainson’s hawks,” said Lamare.

She says 80 percent of the birds nest and mate within 70 miles of Sacramento. Heavy equipment and construction is not allowed near their habitat during this time.

“[It] can be very harmful to the young,” said Lamare.

Caltrans was preparing to start work on Midway bridge on Wednesday.

“In a perfect world, someone would have spotted them earlier,” said Jacala.

But during a secondary inspection last week, the nest was found and the Midway Bridge project was shut down.

“We may push that project off later in the year or indefinitely,” said Jacala.

The Meridian Bridge project will begin on Friday. Route changes can be expected in the area for the next three to six months.