The death of more than 50 bald eagles in two states has scientists looking for answers before more harm comes to the majestic birds brought back from near-extinction over the past 20 years.
“Something is killing them quickly,” said Thomas Roffe, a veterinary medical officer in charge of field investigations at the National Wildlife Health Center in Madison.
Nine birds died this year in southern Wisconsin and 27 more have died in southwestern Arkansas since November. No one knows why.
“Why only bald eagles? It worries us that we might be seeing something here that’s only the tip of the iceberg,” Roffe said.
Environmentalists express the same concern, recalling the drop in raptor populations before DDT was banned in 1972. The pesticide and other chemicals ingested through their prey weakened the birds’ shells, hampering reproduction.
In another 15 eagle deaths in northwestern Wisconsin last April, investigators blame poison - possibly laid by fishermen or hunters irked at the birds’ fish- and game-eating habits.
The national symbol, instantly recognizable by its cap of snowy white feathers and up to 7-foot wingspan, was declared an endangered species in 1967. It retains that status in most of the country, but in Washington, Oregon, Wisconsin, Minnesota and Michigan the population has increased enough to boost its status to protected.
In Arkansas, the eagle deaths involved some toxin that damaged the birds’ brains, while the Wisconsin deaths this year involved one that harmed the birds’ livers, Roffe said.
The mass deaths involve otherwise healthy birds, Roffe said, unlike the 20 to 25 documented Wisconsin eagle deaths each year that are due to lead poisoning or other easily explained causes.
Tests ruled out lead poisoning, pesticides and biological causes, and the center is trying to figure out what’s going on.
One thing ruled out early was the toxic farm pesticide carbofuran - the chemical that killed the 15 eagles last April, said Lynn Creekmore, a disease research specialist with the wildlife health center.