Across most of the lower 48 states, bald eagles increased nearly 2 percent annually from 1986-2000, according to an analysis released by the U.S. Geological Survey.
The analysis was based on more than 10,000 eagle sightings during midwinter surveys in 42 states.
Results of 15 years of the Midwinter Bald Eagle Survey, which involves several hundred scientists and trained volunteers who count eagles from land, water and air, have just been published by the federal agency and Boise State University scientists.
Bald eagles, distinctive from other eagles by their gleaming white heads, live only in North America. The bird has served as the national symbol of the United States since Congress chose it in 1782.
In the middle of the last century, populations declined dramatically due to the accumulation of the pesticide DDT in fish, a staple of the eagle's diet. The pesticides gradually poisoned adult birds and caused females to produce thin-shelled eggs that broke easily, destroying the embryo.
The National Wildlife Federation started the annual survey in 1979, a year after the bald eagle was listed as an endangered species in 43 states. In 1992, the survey was turned over to government scientists.
In 1995, the bald eagle had recovered enough to be reclassified as "threatened" throughout the lower 48 states. Proposals are pending to remove the bird from the list entirely.
"Eagles are one of the great success stories of the Endangered Species Act," said Tom France, director of the Northern Rockies office of the National Wildlife Foundation. "With the protections we have given them and their habitat, they'll soon be ready for delisting."
During the latest study period, eagle numbers increased an average of 6.1 percent in the Northeast; 1.5 percent in the Southeast, and 1.1 percent in the Northwest. The Southwest declined by 0.7 percent.
Scientists are unsure why there was such a dramatic increase in the Northeast.
"We can only speculate," said Karen Steenhof, survey coordinator and a research scientist at the USGS Forest and Rangeland Ecosystem Science Center. "It might be the increasingly warmer winters, which meant more open water," allowing the fish-hunting birds more access to prey.
Steenhof cautioned that the analysis is not conclusive and there is still concern about areas where the birds are not increasing, such as the Southwest.
By Chuck Oxley