By Donna Beth Weilenman
Staff Reporter

Mare Island’s first “San Francisco Bay Osprey Day” celebration will give the public a chance this weekend to see the magnificent birds during their nesting season, said Myrna Hayes, executive director of Mare Island Heritage Trust and Volunteer Preserve manager.

And though it’s called “Osprey Day,” it’s not just a one-day event. It takes place both Saturday and Sunday.

The event will let island visitors take guided car, walking and boat tours and be part of a “citizen science” gathering at the preserve’s visitors center, where they’ll see slide shows of images by Eric Dugan and Tim Buckley.

And because fish makes up nearly all of an osprey’s diet, fish tacos will be available for purchase.

The festival celebrates a change in osprey behavior, Hayes explained.

“Until recently, osprey have been described as occasional visitors to San Francisco Bay by wildlife management agencies,” she said, but several nesting pairs have been seen in the Bay Area, particularly at the confluence of the Napa River-Mare Island Strait and the Carquinez Strait, and on and near Mare Island.

That caught the attention of the Golden Gate Raptor Observatory, Hayes said.

“Osprey have been nesting in very small numbers for more than a decade in the Bay, but for the second season volunteer monitors for the Observatory have documented osprey nesting on the Bay in much greater numbers,” Hayes said.

In fact, Tony Brake and Harvey Wilson, members of the wildlife research organization, determined that the number of hatched osprey chicks increased from 17 in 2012 to 45 in 2013.

Because of this significant increase and a growing public interest in ospreys, the Mare Island Heritage Trust decided to organize the first San Francisco Bay all-osprey event, Hayes said.

The trust manages the Mare Island Shoreline Heritage Preserve, where many osprey nests have been built.

Trust members decided the public should have an opportunity to take a two-hour morning boat trip along the Mare Island shore to see the nests for themselves, as well as to watch soaring adult and fledgling ospreys in the sky.

Event attendees may ride aboard Dolphin Charters’ River Dolphin for $20 each, and join in free guided car tours of nests on Mare Island, as well as walking tours in the Mare Island Preserve.

“On all of the outings, the public will see nest sites up close,” Hayes said. Field guides from the Golden Gate Raptor Observatory, the Audubon Society, Mare Island Heritage Trust and other groups will accompany visitors, she said.

The lunchtime citizen science gathering at the visitors center is a slide show program by local photographers Dugan and Buckley, after which Brake and Wilson will describe their observations and lead a discussion about future needs for programs that monitor, band and record ospreys.

They’ll also explain how members of the public can participate in observing and protecting ospreys that are making their home in the Bay Area.

After the science gathering, those interested may participate in afternoon and evening guided osprey-viewing outings in the preserve.

“In talking together with our volunteers and Tony and Harv from the observatory, we really felt like this was the time to get an event together,” she said.

Another reason the trust organized the Osprey Day festival is “so that we would have a jump-start on what we need in place for the next nesting season, which starts about April and reaches its peak in late June and early July,” Hayes said.

She said preserve strollers already are returning from their walks and reporting their observation of nests with both adults and young. “We have been seeing the numbers of nests and chicks just grow exponentially in our preserve,” Hayes said.

The ospreys are building nests on the island’s abandoned Navy shipbuilding cranes, now idle, and abandoned light poles and other structures, “including the most amazing one of all, a palm tree,” Hayes said.

She said the preserve has an added bonus for bird viewing: its many trees close to the river, where the young birds perch as they learn to fly. They also use the island’s abundance of lightning rods that were placed throughout the former Naval Ammunition Depot that is now the preserve acreage.

The preserve was established when the first parcels were transferred to Vallejo in 2002 by a grant from the Legislature through the California State Lands Commission, stipulating that the property be used for a public trust, such as a park. More land was transferred in 2010. The remainder of the 215-acre site is being cleaned by the U.S. Navy.

Visitors to the preserve may walk or ride bicycles on a paved roadway trail that has 14 interpretive stops along its three-mile round-trip route that leads to the top of Mare Island Hill and beyond.

Among the features of the preserve are scenic vistas of seven Bay Area counties, including Mount Diablo, Mount Tamalpais and Mount St. Helena, the Carquinez Strait, Sonoma and Napa valleys, and the U.S. Navy’s first cemetery in the Pacific, founded in 1858.

Benicia Plein Air artists are exhibiting their paintings alongside interpretive displays at the visitors center in a former munitions storage magazine, Building A-167.

Admission to the preserve is free, both on Osprey Day dates as well as other times throughout the year. But donations are accepted, and are used to help volunteers keep the preserve open.

The San Francisco Bay Osprey Day festival starts at 10 a.m. Saturday and Sunday at the preserve.

The preserve, on Mare Island’s southern end at 1595 Railroad Drive, is open 10 a.m. to an hour after sunset Fridays through Sundays, including the Osprey Day festival. Parking, the main trailhead and the visitors center are at the intersection of Railroad Avenue and 167 O’Hara Court, on Mare Island, Vallejo.

Those interested may call 707-249-9633 or visit the organization’s website, www.mareislandpreserve.org.