A bird researcher has found northern gannets returning to a large nesting colony south of St. John's are faring well despite concerns that a massive oil spill that began in the Gulf of Mexico a year ago would dramatically cut the area's population.

Northern gannets from six colonies in Newfoundland and Labrador and Quebec migrate to winter in the Gulf annually.

Bill Montevecchi, a Memorial University researcher who has been tracking the birds' journey to the Gulf of Mexico and back again, said Tuesday hundreds of the gannets were likely killed by oil that spilled after a rig explosion on April 20, 2010.

A year later at the Cape St. Mary's colony in eastern Newfoundland, Montevecchi said he believed there are signs that some of the thousands of birds that return to the province to lay just one egg each year have been damaged by the spill.

"We think we saw a few birds that had a few spots of oil on them over there." he said.

Despite some signs of oil, Montevecchi said he's optimistic about the future of the colony, but he would keep an eye on what happens there in the future.

It's still not clear what impact returning to the Gulf of Mexico year after year will have on these birds.

"I have a really good feeling. I have a real concern for what happened, and we should minimize those occurrences," Montevecchi said. "There might be some population effects."

Scientists who studied the Exxon-Valdez spill in Alaska suggest the worst might not be over.

Wildlife ecologist Dan Esler, with the Centre for Wildlife Ecology in Delta, B.C., found that lingering residual oil from that spill continued to show up in harlequin ducks.

"Those affects had a sort of demographic trickle-down effect for another decade after that. So a full two decades after the oil was spilled, we hadn't seen a full population recovery," he said.

Esler said it could take years or decades to know the true environmental toll on the Gulf spill.