Researchers with the Cornell Lab of Ornithology in Ithaca, New York have discovered hundreds of pelicans and terns exposed to oil in the largest seabird nesting area of Louisiana. The researchers arrived at Louisiana’s Raccoon Island, home to as many as 10,000 birds, on July 11 and reported their observations to the media on Wednesday.

The Cornell team saw as many as three to four hundred oiled birds on the island, with 30 to 40 of them oiled “head to tail,” in the words of biologist Marc Dantzker, the team’s leader. Dantzker told the Associated Press, “This is a major oiling event of an incredibly important seabird colony. Many of these birds will be dead soon—weeks and months. These blotches are deadly.”

The number of oiled birds discovered by Cornell researchers suggests the official numbers reported by federal agencies responsible for collecting animals contaminated by oil in the Gulf may underestimate the true level of damage done to the region’s wildlife. Lisa Williams, a biologist with the US Fish and Wildlife Service, reports far fewer numbers of oiled pelicans on Raccoon Island than observed by the Cornell team, telling the Associated Press her researchers had only discovered 68 oiled pelicans there.

The latest report issued by the Fish and Wildlife Service indicates a total of 3,128 birds have been collected by rescuers since the oil spill began. Of these, 1,978 were found dead. No less than 1,896 of the birds collected were described as “visibly oiled.” These numbers, which point to a major ecological disaster in the Gulf, may in fact underreport the reality on the ground; birds in nesting areas, as observed by the Cornell team, are not typically included in the official numbers.

Responding to the very low numbers reported by Williams and the Fish and Wildlife Service, Dantzker told the AP, “Come out and look with us. If you’re on the island and using binoculars you will see those birds.”

In a recent statement, Dantzker also reports the birds’ habitat is not well protected. “The island,” says Dantzker, “has a single line of inshore boom on the bay side, and in some places this boom showed signs that oil splashed over the top and there was oil on shore behind these booms. What Gulf-side boom there previously was has been destroyed and is washed up in piles, or deep into the island.”