How many  birds were killed, injured or otherwise affected by the millions of gallons of oil that rushed toward shorelines?

That’s one of the major questions federal scientists and state biologists are wrestling with as they approach the anniversary of the disaster. The Deepwater Horizon rig exploded and sank off Louisiana’s coast April 20, killing 11 crewmembers and unleashing more than 170 million gallons of crude into the Gulf of Mexico. The oil lapped into marshes, beaches, barrier islands and other nesting places for thousands of birds that inhabit the Gulf.

The official count is 8,065 live and dead birds affected by the spill, according to U.S. Fish and Wildlife Service reports. That number includes 932 pelicans and 3,300 laughing gulls, the reports show.

The total count is certain to spike dramatically, says Melanie Driscoll, the National Audubon Society’s director of bird conservation for the Gulf of Mexico, who has assisted in the bird counts, consisting of birds that volunteers and workers actually saw. Thousands more hit by the crude likely sank to an unrecorded death in the marshes, bayous and deep waters of the Gulf, she says.

“Injury to animals is not just a death count,” Driscoll says. “It’s also something that could affect their fitness or longevity or reproductive ability for years to come.”