VALLEJO — The osprey is making a comeback.
The large raptor with an almost exclusive appetite for fish has settled in scattered locations among the decrepid fixtures and structures of Mare Island. What once was a thriving U.S. Naval Shipyard has evolved into a manmade habitat for the sea hawk that has been absent from the surrounding shoreline.
“One-hundred-and-fifty years of Navy has gone wild,” said Myrna Hayes, volunteer Preserve manager with the Mare Island Heritage Trust.
Birdwatchers and citizen scientists were among the crowds that flocked to the Mare Island Shoreline Heritage Preserve this weekend for the second annual San Francisco Bay Osprey Days.
Hayes estimated 900 to 1,000 visitors ventured to the festival for guided hikes, boat tours and presentations all centered on the osprey – a hawk that can measure 2 feet in length with a wingspan up to 72 inches.
“There’s this passion all over the world over the same bird,” she said.
Diane Rooney, who helped lead a viewing hike Sunday in the preserve, said there are many qualities that make an osprey unique.
The osprey is adapted to fishing, she said. Its reversable talons allow the hawk to secure its prey in an aerodynamic manner.
“It looks like they’re surfing on a fish,” she said.
Mare Island’s scattered osprey nests are found atop light poles, industrial cranes, electricity towers and the flattened fronds of a palm tree.
Blogger and photographer Richard Bangert, of Alameda, participated in the guided hike and saw ospreys on various light poles and the irregular palm tree.
“Mostly (they were) just sitting around – preening,” he said.
Tony Brake, of the Golden Gate Raptor Observatory, said the bird is relatively tolerant of humans and its young are known to return after a couple of years to the established nests, which are frequently found on company property.
“The problem with osprey – they tend to build nests on manmade structures,” he said.
Brake said there are methods to protect nest sites and ways to provide an alternative nesting platform as part of a deterrent process.
“We’re trying to get businesses . . . to use these practices,” he said.
Brake hosted presentations this weekend with fellow Observatory member Harvey Wilson titled “Osprey in the Bay: Comeback or Arrival?”
The duo conducted a survey in 2013 that counted the young osprey and nests within 100 meters of the San Francisco Bay shoreline.
Wilson said in the beginning of 1999 only one osprey pair nested on Mare Island. Last year, there were 44 young osprey along the bay’s shoreline, he said.
“The number of ospreys has increased year-by-year all around the bay,” he said.
The bird’s breeding boundary was considered to be farther north in the area of Marin County, Wilson said.
“Since 1999, the boundary is slowly moving south through San Francisco Bay,” he said.
Wilson attributed improving environmental conditions and efforts by municipalities, agencies and organizations to the osprey’s success.
“The bay recovered ecologically and maintained a high standard of environmental quality,” he said. “It’s really a success story.”
Reach Adrienne Harris at 427-6956 or [email protected] Follow her on Twitter at www.twitter.com/aharrisdr.