RIVERVIEW — Glide into Bird Island Cove after rocking through the chop of Tampa Bay and the change is immediately noticeable: water so calm it could be in a bathtub.
The birds notice it, too. Standing wing to wing on sand spits, they peer into the clear depths for fish, preen their feathers, jabber and squawk. Adult birds coach offspring in first flights.
The little sea sanctuary comes courtesy of Bird Island, a slender, curved finger of soil dotted with trees and shrubs that cradle an aquatic haven half a mile or so from the Riverview shoreline.
"It's important to have this habitat," said Mark Rachal, a field biologist with Audubon of Florida's Coastal Islands Sanctuaries program. "They (wildlife) need a space to do what they do."
But the cove is in danger. Just around the corner, on the island's south side, the land takes a daily beating. Wind and ships surging between bayside ports and the Gulf of Mexico whip up waves that relentlessly slap Bird Island's shore. Toppled trees bear witness to erosion.
That's why Audubon, with $84,500 in grant funding, installed 425 linear feet of low-acid concrete reef balls a few yards off the edge of Bird Island in mid April. The hollow orbs, which look like domes with holes cut in them, are expected to absorb wave energy and boost bird foraging opportunities by attracting oysters, barnacles and small fish.
Each of the 212 structures stands 3.5 feet tall and weighs about 1,200 pounds. Contractor Reef Innovations used a crane to place them carefully side by side, leaving periodic breaks to allow dolphins and manatees an escape route in case they find themselves behind the erosion control line.
Erosion has long been a problem at Bird Island and its neighbor, Sunken Island, a pair of spoil mounds that make up the Richard T. Paul Alafia Bank Sanctuary. Rachal points to the remains of piles of tires, a 30-year-old attempt to battle the tides.
More recently, two attempts to anchor the shoreline with cordgrass failed, Audubon regional coordinator Ann Paul said.
Unlike riprap and other techniques that hug a shoreline, the reef balls placed in the water off the island's edge won't interfere with beach access for horseshoe crabs and other critters that find it difficult to maneuver over rubble, Paul said.
Every year, up to 12,000 bird pairs nest at the Alafia Bank, representing 16 or 17 species. It's the top nesting site in the state for roseate spoonbills, Rachal said, and it's considered a critical wildlife area by the Florida Fish and Wildlife Conservation Commission. Ibis and brown pelicans nest in the trees, while American oystercatchers and other shorebirds scoop out ground nests.
Until heavy storms stripped the mangroves in the late 1980s, Bird Island reigned as one of the most significant coastal nesting sites in the United States. After that, the birds moved their nursery next door to Sunken Island, but they still use Bird Island and its protected cove for foraging and respite.
If the reef balls prove successful, Audubon hopes to reintroduce mangroves to Bird Island, thus providing more nesting choices for the birds, Paul said.
Also watching the project is Hillsborough County's Environmental Protection Commission, which awarded $75,000 in grant money from its Pollution Recovery Fund, a pot fueled by penalties assessed for environmental violations. Officials said the commission awarded the grant to help preserve an important bird rookery.
The Tampa Bay Estuary Program kicked in another $9,500 for the project.
"We are so fortunate to have those bird islands in Tampa Bay," said Nanette O'Hara, spokeswoman for the estuary program. "They are so important not only regionally but for the state and even the country."
Susan Marschalk Green can be reached at email@example.com.