Some of the most devastating pictures after big oil spills are of seabirds coated in black sludge. But a new study reveals that even a small amount of oil could cause major damage to bird populations like the western sandpiper. Just a smudge on their wingtips and tails makes it much harder for them to fly than normal birds, researchers have found, which could prevent them from reaching their breeding grounds in time.
The findings are significant because they suggest that even minor oil spills can have a big impact, says Christy Morrissey, avian ecotoxicologist at the University of Saskatchewan in Saskatoon, Canada, who was not involved in the research. “There are ongoing small oil spills around the world that continue to affect shoreline habitats,” she says. “They don’t necessarily make the news, but still they’re happening.”
For years, scientists have been trying to estimate how small amounts of oil would affect bird flight, and in 2013, a team of ecologists at the University of Western Ontario in London, Canada, set out to find out. The researchers used western sandpipers, one of 93 shorebird species that saw their numbers decline after the 2010 Deepwater Horizon oil spill in the Gulf of Mexico. For months following the 1-million-metric-ton-spill, it was common to find birds on the beach with lightly oiled feathers, says ornithologist and study lead author Ivan Maggini. “We figured that just having oil on wings’ feathers might affect their main function, which is flight.”
The team trained 24 western sandpipers to fly inside a wind tunnel for 2 hours at a stretch. Then, using a small paintbrush, the researchers applied a smudge of crude oil from the Deepwater Horizon well on the wingtips and tails of half the birds and flew them alongside birds whose feathers were oil-free. Using a magnetic resonance scanner, a noninvasive instrument that can peer deeply inside the body, the scientists measured the amount of fat in each bird before and after the 2-hour flight test—a proxy for how much energy the birds spent. Sandpipers with oil on their wingtips and tails—less than 20% of their body—consumed 22% more energy than oil-free birds, the team reports today in the Journal of Experimental Biology.
When the researchers also spread oil on the birds’ backs and bellies—around 30% of the total body surface—the increase in energy use per flight soared to 45%. What’s more, half the birds with oil on their wingtips, tails, and bodies repeatedly attempted to land and did not complete the flight test. Landing, Maggini says, is the “most obvious sign that they’re getting tired.” Moderately-oiled birds also flapped their wings more frequently and with broader strokes than oil-free birds, which likely made flight more energy expensive. According to Maggini, the presence of oil on wingtips, tail, and body might increase the drag the birds experience—a bit like people trying to run with ankle weights.
“If birds use more fuel, they’ll need additional time to replenish their energy reserves,” Maggini says. For those birds, refueling might take up to an extra week at each stopover. When migrating from the Gulf of Mexico to Alaska, an oiled western sandpiper could be delayed up to 45 days, the team calculated. “In the Arctic and the North Slope of Alaska, most nests are initiated within a 2-week period,” says Brad Andres, national coordinator of the U.S. Shorebird Conservation Plan in Lakewood, Colorado. “It’s a tight window: Birds have to get up there, court, do their breeding rituals, lay eggs, raise young, and get out before snow comes in September,” he says. If birds arrive to their breeding grounds late, they’re not going to be able to reproduce, he says.
The findings suggest that even small oil spills could have a dramatic impact on seabirds. 2016 alone saw one large tanker spill in the Gulf of Mexico, discharging over 5000 metric tons of gasoline and diesel, plus four medium-sized spills elsewhere. But the problem with small spills, which account for the vast majority of incidents, is that they often go unreported, Andres says. That makes it hard to calculate the damages due to lost reproduction. Every year, as many as several million birds could be affected, he says.
That’s bad news for birds already suffering, Morrissey says. For reasons still under investigation, most shorebird populations have declined about a 50% over the last 30 years, she says. “We need to consider the consequences of the demand for more oil and what that does to the environment.”
Still, says Morrissey, more research needs to be done to determine precisely how small amounts of oil affect the birds. It’s possible, she says, that the oil isn’t hurting the birds by increasing drag, but by poisoning them via accidental ingestion. Either way, it’s bad news.