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By Rick Jervis, USA TODAY
NEW ORLEANS — Pictures of pelicans slathered in oil during last summer's BP oil disaster became iconic images of the event.
How many total 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."
During the 1989 Exxon Valdez oil spill in Alaska, biologists initially counted about 30,000 affected birds, but that number later soared to 250,000 after calculations were made to include birds that were likely impacted but not seen, Driscoll says.
"You can't always tell by sheer number of birds collected what effect on the population will be," she says.
More than 300 species of birds live or pass through the Gulf Coast each year, including some rare and endangered species, making it one of the most important bird habitats in the world, Driscoll says.
Estimating the number of unseen impacted birds is no easy task, especially in the warm, shark-infested waters of the Gulf of Mexico, scientists say.
Last month, federal and state biologists began fanning across the Gulf, trying to come up with a good formula, Driscoll says.
Many factors are being considered. For one, the region's warm temperatures may have disintegrated many of the remains of birds killed by oil before they were found, she says.
Biologists at the start of the disaster agreed not to disrupt sensitive breeding colonies looking for affected birds, opting to wait until after the breeding season ended in September. That left five months for birds to die and disappear without a trace, Driscoll says.
"There are huge areas where searches could have been done without finding any birds," she says.
Another factor is the Gulf's predatory ecology. Sharks and other predators lurking below the surface could have pulled down pelicans or other birds slowed by the oil, says Peter Tuttle, a Fish and Wildlife Service project leader involved in the count.
To measure how often this may have occurred, biologists starting in June will conduct a "carcass drift study," he says. Remains of birds are dumped overboard deep in the Gulf and tracked to see how long it takes them to reach shore — if it all, Tuttle says. The results are factored into the final calculations.
Other tests include dropping bird carcasses in marshes and on barrier islands to time how long they remain in recognizable form, he says. Many of the tests are being done in the Gulf for the first time.
"We don't have a good handle on the Gulf," Tuttle says. "These studies have been done in California and up in Alaska, but haven't been done on the Gulf."
Biologists across the Gulf Coast also are measuring what the long-term impact could be on the reproductive systems of the region's birds, says Todd Baker, oil-spill coordinator for the Louisiana Department of Wildlife and Fisheries, who has been involved in assessing the spill's damage to the ecosystem.
Many of the region's brown pelicans, terns, skimmers and other shorebirds may have escaped direct contact with the oil but are starting to nest in beaches that still have oil lurking just beneath the sand, he says.
Biologists are studying to see whether the birds nest on the oily beaches or find other suitable areas, Baker says.
Scientists also are trying to decipher what effect Corexit, a chemical dispersant sprayed at the underwater oil geyser by the thousands of gallons, and other chemicals could have on birds' long-term reproduction and survivability, says Driscoll, the Audubon Society biologist.
Birds such as the common murre and pigeon guillemot recovered slightly shortly after the Exxon Valdez spill, then saw their numbers plummet the next decade, she says.
