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Oil Spills Are Even Worse for Birds than We Thought

A new study finds that even small smudges of oil can have huge impacts on flight and a bird’s energy budget.

A partially oiled gull near the 2007 San Francisco Bay oil spill

Ingrid Taylar/Flickr

Anyone who has ever seen a picture of a pelican covered in black crude knows that oil spills are bad for birds. The sludge gums up their feathers, neutralizing their ability to repel water and conserve heat, which leads to hypothermia. For seabirds, oil can sink their natural buoyancy and literally drag them into a watery grave. And the birds that try to clean themselves ingest a sticky poison that ravages their livers, lungs, and intestines.

Some lucky ones, however, get away with just a few smudges. And yet, according to a new study published July 1 in the Journal of Experimental Biology, even small amounts of oil can create problems for a bird down the line.

“Feathers are the most important feature of a bird,” says the study’s lead author, Ivan Maggini, an ornithologist at the University of Western Ontario. They allow birds to jump off the ground and soar into the air, plunge at incredibly high speeds, and even shoot in and out of water. But these feats are only possible if a bird’s feathers are unencumbered.

The researchers grabbed up a bunch of supercute shorebirds called western sandpipers and used a paintbrush to dab the tips of their wings and tail feathers with varying amounts of crude taken from the 2010 BP spill. The scientists then threw them into a wind tunnel to see what would happen (but, you know, gently and ethically).

The result? Birds with just a light coating of oil covering less than 20 percent of their body surface had to expend approximately 20 percent more energy than birds flying oil-free. When the researchers added a slightly heavier layer of oil on about 30 percent of the birds’ body surface, including feathers on both the breast and back, the western sandpipers spent upwards of 45 percent more calories to fly than the control group.

A western sandpiper in Nome, Alaska

Mick Thompson/Flickr

Migratory birds, particularly small ones that cover gigantic distances, are even more vulnerable since they rely on fat stores for every leg of their journey. Just like the gas tank in your car, a bird can fly only so far before it needs to refuel, and oil on the wings is the equivalent of getting fewer miles per gallon. Maggini and his colleagues haven’t determined exactly why this is yet, but their best guess is that even tiny blots of oil increase drag—like a greasy black ball and chain, he says.

Couldn’t the birdies just pull themselves up by their birdstraps and work a little harder? The answer is yes and no, but Maggini says, “It’s not true that a bird that survives an oil spill might get over it with no repercussions.”

Western sandpipers with oiled wings will need to stop more frequently on their way north and expend more energy finding food on their stopovers. And while a day here or there might not seem like a big deal to us, for a migrating bird it could mean the difference between a successful breeding season and a colossal waste of time.

Males especially need to get to the breeding grounds early to build scrapes, or depressions used for nests, and guard them until the ladies roll into town and choose their favorite builders. Maggini says early males have been shown to have greater reproductive success.

But striking out with females isn’t the only thing at stake here. Another recent study by Maggini, published in Ecotoxicology and Environmental Safety, shows that western sandpipers with oiled wings are slower to take off when startled—and their escape trajectories are 10 degrees lower. With such sluggish getaways, oiled birds may be easy pickings for predators, vehicle strikes, or other dangers.

Maggini says he and his coauthors were surprised that such small amounts of crude could influence flight mechanics so greatly. Oil spills are obviously environmentally disastrous, but the findings give us new perspective on just how potent the consequences are for wildlife.

The new science arrives as President Trump is calling for the opening of new waters to drilling in the Atlantic and Arctic, two crucial migratory regions for birds from all over the Western Hemisphere—all while rolling back safety regulations that would help prevent offshore disasters like the BP blowout in the Gulf of Mexico, a spill that killed more than a million seabirds. Given that migratory birds are already contending with habitat degradation, heavy levels of mercury released by melting sea ice, and potential food shortages brought on by climate change, maybe it’s a good time to not throw oil into the mix.


onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.

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