New USFWS Study Looks at Number of Birds Killed in Last Year

Photo: Kim Hubbard, for Audubon magazine

Last year’s massive oil spill may have fallen from the front pages, but it’s still top of mind for the U.S. Fish and Wildlife Service. As part of its Natural Resource Damage Assessment and Restoration, the agency continues to crunch numbers and conduct research to determine closer-to-real consequences of one of the nation’s worst environmental calamities.

Hence the start of a three-part USFWS study, funded by BP, that looks at how far and to where an oiled carcass may drift, how long the carcass lasts once it comes ashore, and how efficient it is to survey beaches for dead animals. The end goal: To figure out how many birds the Gulf Oil Spill actually killed.

“With these three studies, you get a probability of the carcass reaching the land, that it persists, and that a searcher finds it. Those three things get combined into a probability of recovery,” says Melanie Driscoll, Audubon’s director of bird conservation for the Gulf of Mexico and Mississippi Flyway. “That probability of recovery doesn’t give you one estimate of the actual mortality. It gives you a range.” One, she adds, that could be rather large.

In other words, it’s not an exact science. But Driscoll says that doesn’t matter, mostly because the results of this research will produce better estimates than are currently available. “What we have right now is a number of birds recovered that everyone assumes is a minimum estimate of mortality,” she says. “Every piece of information you get gives you the ability to get to a truer estimate…. You’ll never know what the real number [of birds killed] is, but you understand the likelihood that you’re approaching a real number.”

To get this data, USFWS conducted five drops, the last of which happened in early August, lowering into Gulf waters 248 bird carcasses and 66 dummies attached to buoys with antennas. The birds can float and the USFWS tracks their paths using radiotelemetry, says agency spokesperson Nanciann Regalado. After two weeks of collecting information, USFWS will analyze the results. (As of press time, Regalado couldn’t say when the USFWS would have final numbers.)

Because the Carcass Drift and Persistence Studies weren’t conducted last year, during the spill, many factors—wind, water temperature, number of tropical storms, etc.—will be accounted for in the modeling process, Regalado says. Also, in no other spill was such a large amount of dispersant used, so that also needs to be included, Driscoll adds. “The study’s not perfect,” she admits. But “you at least have something that is calculated and defensible.”