Carbon from oil has been found in marine species, but this is the first time evidence of oil from the spill was found in a terrestrial vertebrate species.
Researchers collected sparrows from areas documented to have been contaminated and areas that did not receive any oil. The birds were collected from the Barataria Basin one year after the spill, which occurred in April 2010.
“These birds are not migrants, and their habitats are restrictive, meaning they just can’t move to a wooded area or retreat to the levees. They reside in a salt marsh habitat,” said Philip Stouffer, one of the researchers on the project. According to Stouffer, the presence of carbon from oil in both their feathers and their gut contents indicated it was from a chronic or long-term exposure.
Because the birds are year-round residents, they could not have gotten the oil from another source, Stouffer said. Sources of the oil could have come from any food source consumed by the bird, including insects, small invertebrates and seeds, he said.
The researchers used sophisticated equipment to determine the oil in the sparrows was from the Deepwater Horizon spill. Stouffer said an examination of hydrocarbons in marsh sediment confirmed the Horizon spill as the source through a process called oil source fingerprinting.
Samples of the feathers and stomach contents were sent to Rafter Radiocarbon Lab in Lower Hutt, New Zealand, to be analyzed.
Researchers are not sure of the implications of finding the oil in the sparrow, Stouffer said. Data from other research indicate that reproductive success initially was lower in areas that were oiled, but success rates recovered several years after the spill.
Other research indicates that oiled areas also had a reduction in organisms such as insects, spiders and other invertebrates that play an important role in the diets of the seaside sparrow. This decline in food resources, along with habitat loss from the oiled areas could have played a significant role in reproductive failures for the first few years after the spill, Stouffer said.