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TWo biologists on a beach wearing gloves photograph and document a dead sea gull.
Information icon A USFWS biologist documents the GPS coordinates for a dead gull found in Gulfport, Mississippi, during the Deepwater Horizon oil spill. Photo by Bonnie Strawser, USFWS.

Service employees lead studies on toxic and physical effects of oil on birds

Kate Healy, a Southeast region biologist working at the Service’s Fairhope, Alabama, field office sighed deeply when asked to describe her role in assessing the devastating effects of the April 2010 Deepwater Horizon oil spill on birds. “Well, that was tough work… not physically, but emotionally,” she said after a brief pause. “Much of my work involved exposing birds in the lab to the same toxic substance we knew had already killed thousands of birds in the field. But we had to do it. Our job was to estimate the injury the Deepwater Horizon oil spill inflicted on birds across the Gulf of Mexico.”

The Deepwater Horizon Natural Resource Damage Assessment Trustees had the daunting task of assessing injury to the wildlife that live all or part of their lives in the Gulf of Mexico region. The Service led efforts to complete the assessment for avian species.

A biologist in uniform kneels next to a gull carcass to read numbers from a handheld device.
USFWS biologist records a gull carcass on Gaillard Island near Mobile, Alabama, during Deepwater Horizon recovery efforts. Photo by Michael Assenmacher, USFWS.

The trustees relied on two approaches to assess injuries to migratory birds. The Shoreline Deposition Model used data on the deposition of impaired and dead birds on shorelines, such as the chances dead oiled carcasses would make it to shore and the likelihood of them being found by searchers, and other data to estimate mortality across the Gulf.

The Live Oiled Bird Model estimated injury to birds that were oiled, but did not immediately die from the exposure. This second approach relied on four kinds of dosing studies. One used direct oral doses and another involved application of oil to birds’ feathers. The toxicological effects of these kinds of exposure were analyzed and used to estimate the fate of the thousands of bird in the field that were observed with oil on their feathers. Another study looked at the impact of oiled feathers on a bird’s metabolism, thermal regulation, and ability to fly. The final approach was a field-based look at the effects of oiling on flight.

Healy summed up what Service employees found through investigations they either managed or conducted with one word: “Significant.” “The study results, when taken together, indicated that even light oiling, which we had thought some bird could survive quite well, may be far more detrimental than we ever expected,” she concluded.

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