At a scientific conference this week hosted by the US Minerals Management Service, University of Alaska doctoral student Stacia Backensto said nesting ravens are enjoying a near 90 percent success rate in producing fledglings. That is far higher than the normal fledgling success rate for ravens in similar settings.

The oil-field ravens use industrial scraps to build nests on the undersides of pipelines and on other oil-field facilities, she said. And they are feeding from the Prudhoe Bay landfill to survive during the otherwise food-scarce winters.

But what is good for the ravens may be bad for other wildlife, Backensto said. Ravens are voracious predators known to clean out the nests of other birds and also to scoop up small mammals.

"As predators, they have the potential to impact other birds that are nesting around this facility," Backensto said.

During the decades-long battle to open Alaska's Arctic National Wildlife Refuge to oil drilling, opponents and supporters of the plan have scrutinized the environmental impact of existing and future development on the region's wildlife.

The Senate on Wednesday voted to open the refuge, which lies east of Prudhoe Bay, to oil drilling.

Stan Senner, who works in Alaska for the environmental lobbying group the National Audubon Society, agreed the ravens population at Prudhoe Bay was on the rise. He said annual bird counts conducted at Prudhoe Bay showed a steady increase in ravens, from practically none in the early 1980s to about 100 birds at last count.

But Senner said "ravens don't belong on the coastal plain of the North Slope."

He also cited a 2003 report by the National Research Council on the environmental effects of oil exploration on the North Slope, which said "increased predation (by various animals) on nests is the most apparent effect of oil development on birds that nest in the oil fields."