Common redpolls, goldfinches, evening grosbeaks and other songbirds are getting sick and dropping dead across at least 15 Midwest and Northeast states, The Grand Rapids Press reported Tuesday.
Salmonella infections, spread by bird feces left at feeders and other places where birds flock, are to blame.
"It's widespread this year," said Bob Humphries, district wildlife biologist for the Michigan state Department of Natural Resources. "It's very difficult to control. With the congregation (of birds) at feeding sites, it's just more easily transmitted."
Connie Sheneman knew something was wrong last fall when she spotted a redpoll staggering near a bird feeder. Disoriented and unable to fly, the small songbird didn't last long.
"It was walking around and acting all sick and weird. It's just really sad," said Sheneman, 43, who lives near Michigan's Big Pine Island Lake. Sheneman since has picked up at least 30 dead redpolls and two goldfinches around the many bird feeders in her back yard.
"They died all winter long. Their eyes get all matted, and they get (their feathers) all fluffed up," she said. "You can see them hobbling around, and they can't hardly fly. It's just really sad."
The salmonella outbreak may have started last fall, though researchers only recognized the regional nature of the problem in January.
"We really have not seen such a die-off over such a wide geographic area in the 25 years that this center has been here," said Kimberli Miller of the U.S. Geological Survey's National Wildlife Health Center in Madison, Wis. The center tracks diseases in free-ranging wildlife across the nation.
This is the first year Michigan wildlife officials have seen the problems spread from house sparrows to other songbirds, particularly redpolls, though finches, evening and pine grosbeaks and cardinals also have been infected.
Since January, the state's wildlife disease laboratory has received more than 270 reports of dead birds in more than two dozen Michigan counties. More than 90 percent of the dead birds were redpolls, a small, finely featured finch marked by a red patch on the forehead.
Wildlife biologist Tom Cooley said songbirds have been hit hard because they're "a flocking-type species that feed as a group and are gregarious. If you attract them into a feeder, you'll have a pretty high concentration."
Sick birds spread the salmonella infection as they "defecate onto the feed while feeding and another bird eats that contaminated feed. That keeps the cycle going," Cooley said.
Although a few western states experience songbird deaths from salmonella every few years, the last major outbreak was reported in New York and some New England states in 1988, Miller said.
It's uncertain why the outbreak is so ntense this year. Experts suspect other factors from the presence of a particularly virulent strain of salmonella to a mild winter that may have aided the bacteria's survival.
Halting its spread could be difficult, wildlife experts conceded. They strongly recommend backyard bird watchers clean and disinfect their feeders once a week with a bleach solution and clean up seeds and feces that spill below and around the feeders.
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