Even light oiling can be harmful to seabirds

see www.sciencedaily.com/releases/2017/10/171012151809.htm

“Many birds and other wildlife die following an oil spill, but there are also other potential long-terms effects of oil exposure on animals. In a recent Environmental Toxicology and Chemistry study that examined blood samples from birds present in the Gulf of Mexico in 2010 and 2011 following the Deepwater Horizon oil spill, even birds with small amounts of oil present on their feathers experienced problems related to their red blood cells.”