A place to come back to

On a foggy morning in April, researcher and bird bander Fred Bassett removed a pale-faced bird with a dark eye-line from a mist net at Fort Morgan State Historic Site near Gulf Shores, Alabama, and held it up for visitors to see.

It was a Swainson’s Warbler, a species that breeds in the southeastern United States and spends the winter in the Bahamas and on Jamaica, Cuba, and other Caribbean islands.

Beautiful and secretive, the bird ranks high on many birders’ wish list, but this one was more significant than that. It was part of the first set of spring migrants to return over the Gulf of Mexico since the Deepwater Horizon rig exploded and sank in April 2010, causing the worst oil spill in U.S. history.

Bassett, whose work with hummingbirds I described in the December 2010 issue (see “Winter Hummingbirds in the Gulf,” page 18), had not observed a reduction in numbers of migrants. “We’re not seeing anything different,” he says, “but most of these birds are land birds. They’re coming back from the tropics, and they don’t light on water. The spill had a heavy impact on seabirds and shorebirds, but beyond that, we just don’t know.”

His uncertainty puts him in good company. It’s been more than a year since the explosion killed 11, injured 17, and released about 200 million gallons of oil into the Gulf. Yet scientists are still struggling to understand how all that oil, and the two million gallons of chemical dispersants that were added to it, affected bird populations.

The scale of the task is daunting.

Oil washed ashore from the Texas-Louisiana border in the west all the way past Pensacola, Florida, in the east, affecting more than 1,000 miles of coastal territory. The list of habitats put at risk includes:

— Sandy beaches, wintering grounds for 40 percent of our population of the threatened Piping Plover and nesting grounds for terns, Wilson’s and Snowy Plovers, American Oystercatcher, and Black Skimmer;

— Salt marshes, breeding grounds for Brown Pelican, egrets, herons, Roseate Spoonbill, and many other birds;

— Tidal mudflats, used by godwits, sandpipers, dowitchers, yellowlegs, Red Knots, and other migrating shorebirds;

— Open ocean, feeding grounds for Wilson’s and Band-rumped Storm-Petrels, Audubon’s and Cory’s Shear­waters, Masked and Brown Boobies, Northern Gannet, terns, and other seabirds. Common Loons and millions of scaup, teal, and other wintering ducks also rely on the Gulf waters.

Seventeen recognized Important Bird Areas were threatened. And in Louisiana, the state hit hardest, oil contaminated marshes and barrier islands for which little baseline data existed, making damage estimates impossible.

Barn Swallow to frigatebird
The number of scientists trying to determine just how many birds were harmed is large. J. Christopher Haney, chief scientist at Defenders of Wildlife, has been crisscrossing the deep Gulf of Mexico for months aboard NOAA research ships under contract with the Fish and Wildlife Service. When a colleague spotted Brown Boobies and Sooty Terns within a few miles of the still-gushing well in June 2010, Haney knew he had evidence that species invisible from land were directly in harm’s way.

Other researchers are looking at the number of oiled birds recovered as a percentage of total birds affected. Figures released on April 20, 2011, by the Fish and Wildlife Service put the number of birds recovered at 9,193, of which 4,389 were visibly oiled. Of the oiled birds, almost half, 2,303, were collected dead. The casualties included a surprising variety of species, ranging from Barn Swallow to Magnificent Frigatebird. Of the birds that were found alive, 1,252 were later released.

Michael Seymour, a nongame avian biologist with the Louisiana Department of Wildlife and Fisheries, says that most of the birds recovered in his state came from just two species: Brown Pelican and Laughing Gull. “Of 1,500 live oiled birds sent to rehab,” he says, “the majority were Brown Pelicans. They’re big and easy to see, and they have some white on them, so the oil would stand out. We also saw a large number of Laughing Gulls. They nest here by the tens of thousands, so you expect them to be heavily affected by the oil. They’re smaller than the Brown Pelicans, so there’s less chance of someone finding them. In third place, I saw Royal Terns, including chicks that were apparently oiled in the colony.”

Melanie Driscoll, director of bird conservation for Audubon’s Louisiana Coastal Initiative, surveyed contamination on islands in Barataria Bay, an estuary of national significance located between Bayou Lafourche and the Mississippi River delta. “We found one to five percent of birds of all species in colonies were contaminated by oil,” she says. “We had parents bringing oil to the young birds in the nest. We were looking at colonies in mangrove swamps where the oil got into the edges of the area. Juvenile pelicans that got out to the edge of the colony got oiled.”

Driscoll’s worst fears were not realized, but she sounds a cautionary note: “Given that our initial fear was complete failure of the colony, the situation was not as bad as we feared, but the problem is, we’re seeing only oiled birds that lived long enough to get back to the colony, not those that were lost at sea. We’re looking at a large area of open water and some small islands.”

Seymour explains that a formula is being developed based on the number of dead birds recovered to determine how many birds were killed. “We know there were birds scavenged, lost at sea,” he says. “We also know that in the case of marsh birds, especially the secretive ones, we weren’t finding them where they were dying in the marsh. We’re working on the numbers now; it will involve taking the total number of birds in a population, seeing how many were found dead, and coming up with a coefficient to determine the probability of detection.”

After the tanker Exxon Valdez struck a reef in Prince William Sound, Alaska, in 1989, spilling about 11 million gallons of crude oil, the number of dead birds recovered was estimated to represent 10-30 percent of the total killed. The BP spill affected a vast area of open water — the area closed to fishing encompassed 88,522 square miles, or about a third of federal waters in the Gulf — where finding dead birds was much more difficult, if not impossible. (And trouble lurked below the surface, too: Researchers have confirmed the presence of a plume — a wide, thick cloud of minute oil droplets as much as 22 miles long — between 3,200 and 4,200 feet down.)

Whatever the final number turns out to be, the public will have to wait to learn it: Numbers gathered as part of the ongoing Natural Resources Damage Assessment won’t be released until they are introduced as evidence in a lawsuit filed by the Justice Department against BP and eight other defendants.

By spring 2011, scientists were shifting their focus from the number of birds killed to the potential for rebound in species that had suffered damage to breeding colonies, such as Brown Pelican. Although massive pelican die-offs were reported last summer on the islands off Louisiana, researchers who visited the coast in September 2010 returned cautiously optimistic.

In a report based on data compiled by the scientists, the National Audubon Society called the gulf “the largest uncontrolled science experiment in our country.” Some of the news was encouraging: Scientists tallied nearly 10,000 individual birds, including large populations of Brown Pelicans, both juvenile and adult. But the birds were observed not to be moving from their preferred habitat even after it had been contaminated by oil, and so were still facing exposure to oil and dispersants.

Seymour says it’s too early to tell whether the pelican population will recover. “We’re going to have to watch this for years. After the Exxon Valdez, we found long-term effects with the Black Oystercatcher — the chicks were smaller and less likely to survive. We don’t know if we’ll see the same in gulls, terns, and pelicans.”

A species’ potential for rebound depends heavily on whether its food supply has been compromised. James Fraser, professor of wildlife in Virginia Tech’s Department of Fish and Wildlife Conservation, is studying the Gulf Coast’s overwintering population of Piping Plover and trying to determine whether the bird’s food resources were contaminated.

“We’re estimating survival of individually banded birds over a wide area — from Louisiana’s barrier islands all the way to Dauphin Island, Alabama,” he says. “The birds overwinter out on the beaches, on intertidal flats, and on the back beaches. The flats produce what they eat — which, in winter, is mostly [bristled, burrowing marine worms known as] polychaete worms. There’s a potential effect on the food chain, but it would be premature to say.”

William Monty Graham, senior marine scientist at the Dauphin Island Sea Lab and assistant professor at the University of South Alabama, offers encouraging news. He notes that, although oil carbon entered the coastal food web during the spill, his studies so far do not indicate the presence of toxins: “Oil is 85 percent carbon, found in thousands of different molecules. Toxic components are usually seen in the form of PAH — polycyclic aromatic hydrocarbons — which we associate with gasoline and which usually enter the watershed by runoff from pavement.”

Graham is studying oil-eating bacteria that were eaten in turn by zooplankton, resulting in the zooplankton taking up carbon-12. He has not found significant amounts of toxins, but he notes that even toxic components of carbon are organic, a fact that makes them less of a risk to the food chain than metals such as lead and mercury: “Organic components such as carbon tend to metabolize, and the higher you go up the food chain, the easier they are to metabolize. Since birds are vertebrates, they tend to metabolize organic compounds, even toxins, readily.”

Besides the potential effect on the food chain, scientists are focused on habitat degradation. Seymour says that beaches were not the only areas affected: “Once oil gets in a marsh, there’s little you can do to clean it up.” Beyond the danger to birds that become oiled through contact with marsh vegetation, a major concern is the oil’s effect on the productivity of the marshlands.

Ecosystem ecologist Just Cebrian and senior marine scientist Ken Heck, both of the Dauphin Island Sea Lab, are currently in the midst of a multi-year study on the state of marshes and underwater seagrass beds in Mississippi and Alabama. Cebrian says that while marshes and grass beds in Louisiana saw “substantial” damage, the areas he is studying have fared better. “The oil hitting Mississippi and Alabama was degraded [that is, it was depleted of its more volatile components] and didn’t come ashore in big quantities. We’ve been trawling in the seagrass beds and setting tidal traps to study marsh dwellers. So far, both the grasses and marshes seem to be doing well, and so are the fish and shrimp in the seagrass beds.”

A football field a day
Contamination is not the only threat facing marshlands, especially in Louisiana. “We’re losing a football field of marsh habitat every day” through erosion, says Kevin Norton, Louisiana state conservationist with the Department of Agriculture’s Natural Resources Conservation Service (NRCS). He was already considering a plan to utilize agricultural land to create shallow-water habitat when the spill struck.

The timing could not have been worse. “Hurricane season was approaching,” Norton says. “The spill had enormous potential to impact critical wetland habitat prior to the migration season. We were looking at a scenario with birds landing in an oil-impacted marsh with inadequate food supply, which could have been devastating.”

NRCS responded with a $20 million initiative that paid landowners to manage their land to enhance water habitat for migrating birds. The aim was not to change migration patterns. “We realized you can’t interrupt a bird’s natural instinct to migrate,” Norton says, “so our goal was to provide quality shallow-water habitat to slow migration and to provide abundant food, so that birds that did reach an impacted marsh could back up and get to a food supply.”

The goal was to include up to 150,000 acres in the states involved; by early 2011, the program had enrolled 470,000 acres, 193,700 of which were in Louisiana.

According to aerial studies conducted by the Louisiana Department of Wildlife and Fisheries, in 2010-11 some 1.4 million ducks wintered in southeastern Louisiana. The habitat program couldn’t keep the waterfowl out of oiled marshes, but it proved valuable in combating a threat that had nothing to do with oil. “As it turned out, the marsh was not impacted by oil as heavily as it was by drought,” Norton says. “Our water level was way down, and salinity was encroaching on the freshwater marshes. Thanks to the program, we provided mudflat, shallow-water, and deepwater habitat for a wide variety of birds, not just migratory waterfowl.”

Norton considers the program a success: “We have a monitoring effort ongoing. During fall 2010 migration, we saw huge numbers of Blue-winged Teal. This winter, we saw a wide variety of birds. We looked at the total migratory scene in designing the program, and as a result, we found dowitchers, sandpipers, Willets, and avocets in large numbers on the mudflats.”

David Ringer, Audubon’s communications coordinator for the Mississippi River and Gulf of Mexico, says that habitat degradation can be deadly for spring migrants: “Birds coming in spring are desperate for the first land they can find. One of the main areas used by these migrants is the Mississippi River delta, a ragged fringe of habitats sticking out into the Gulf. The area is vitally important for shorebirds and raptors as well as songbirds. The Indigo Buntings, Ruby-­throated Hummingbirds, and Chimney Swifts that people see all through the eastern United States probably passed through this affected area.”

Although spring migration proceeded normally in places like Fort Morgan, Alabama, where bander Fred Bassett captured his Swainson’s Warbler, observers in the Louisiana marshes described a grimmer scenario. Visiting the area just before the one-year anniversary of the spill, Audubon’s Melanie Driscoll says she was “incredibly disappointed” to find oil still washing up on the shores of Grand Isle, which is a part of the Barataria Terrebonne Important Bird Area and an important rest stop for spring birds.

She found evidence of habitat loss — heavily oiled marshland showing no signs of new growth. The marshes are key habitat for year-round species such as Seaside Sparrow as well as migrants like the Red Knot. Greg Butcher, director of bird conservation for the National Audubon Society, says the spill’s effects on long-range migrants may never be known because once they leave the coast, they disperse over a wide range.

Efforts to restore habitat are underway. One, a submerged breakwater reef installed in Bayou la Batre, Alabama, to protect aquatic vegetation and create habitat for oysters, is being hailed as a model for the sort of recovery effort that could make a difference in the long-term health of the Gulf’s bird populations.

Ringer says that such projects are crucial. “Birds are resilient if they have healthy habitat and if the food webs are intact. Birds can overcome disasters — but only if they have a place to come back to.”

Kathie Farnell is a writer and independent radio and television producer based in Foley, Alabama. She also wrote about Fred Bassett’s work with hummingbirds that winter along the Gulf Coast.

Originally Published August 26, 2011