June 8, 2009
Smithsonian scientists have determined just what forced Captain Chesley “Sully” Sullenberger to land U.S. Airways Flight 1549 in the Hudson River on January 15: migratory Canada geese that had probably come to the area looking for food and open water in response to a cold snap and snow on their wintering grounds.
When I spoke with Carla Dove, head of the Feather Identification Lab at the National Museum of Natural History, the day after the incident, little was known about what caused the crash except that birds were likely behind it. But she spoke about the importance of finding the culprits:
If we know what species of birds are causing the problem, causing damage to aircraft, then we can give that information to the airfields and they can do something to prevent that from happening [in the future].
Determining the species wasn’t all that difficult. Dove and her lab received nearly 100 samples of material in three batches from the two engines, one of which had sat at the bottom of the Hudson for nine days. They used morphological analysis and DNA barcoding to determine that Canada geese (Branta canadensis), a bird that averages eight pounds in size, had struck the plane’s engines. (This was a relief to engineers, as the Airbus 320 had been designed to withstand birds of up to four pounds.)
But were they migratory geese or residents of the area?
Dove turned to Peter Marra, an ornithologist at Smithsonian’s Migratory Bird Center at the National Zoo. In his own research on population abundance of migratory and resident birds, he had been using a technique called stable isotope analysis that lets scientists make inferences about animals’ lives, like what they have been eating. One isotope, deuterium, varies by latitude.
Marra calls the feathers recovered from a plane after a bird strike another “black box recorder” that can provide information about what happened. In the case of Flight 1549, those feathers would tell where the birds had come from. Because migratory Canada geese molt before they migrate, their new feathers are laden with the deuterium of their last home (either their breeding or wintering grounds, depending on the time of year). Resident birds, though, will have a different deuterium signature that reflects their home grounds.
Marra and Dove compared the deuterium signatures in the feathers from Flight 1549 with samples from two known migratory subpopulations and six resident geese. Their analysis indicates that the birds that struck the Hudson plane were migrants from the Labrador region subpopulation. However, it wasn’t the right time of year for them to be migrating through New York. Instead, the scientists hypothesize that the birds had been in their wintering grounds but that freezing temperatures and snow on the ground prompted them to search for open water and food. (Airports, often built on former wetlands, are tempting areas for many bird species.) Exactly where the geese had been wintering is still a mystery, however. “These patterns of migration are really unknown for many species,” Marra says.
Also still to be determined is the exact number of birds that hit each engine. The scientists determined that one engine held DNA from at least one female and one male bird, while the other had DNA from at least one female.
There are thousands of reported birds strikes every year, but the FAA estimates that this reflects only about 20 percent of the total, as reporting is not currently required. Dove and Marra would like to see more reporting in addition to better data on the migratory patterns of birds. “We’re sharing the skies” with billions of birds, Marra says. They can be managed to minimize the danger around airports, but more data is needed to create better tools for bird management, says Dove.
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