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Deformed Chickadees Baffle Bird Experts

In 1991, a man living in King Salmon noticed three black-capped chickadees with beaks curved like fishhooks. Since then, hundreds of people from Southcentral Alaska have seen chickadees with overlong beaks that make it difficult for the birds to feed. The drastic increase in sightings has biologists worried that something is very wrong in Southcentral.

As of late March 2000, biologist Colleen Handel of the U.S. Geological Survey in Anchorage has received more than 400 reports of black-capped chickadees with deformed bills in Anchorage and the Mat-Su valley. The magnitude of the problem becomes a bit clearer when Handel points out that bird-watchers throughout the rest of North America reported just eight sightings of chickadees with similar ailments since 1986.

Handel said 60 percent of the sightings have been in the Mat-Su valley and another 35 percent of those reports have been in Anchorage. People have also seen the deformed chickadees in Kenai, Soldotna, Homer, Valdez, King Salmon, and near Matanuska Glacier. Further north, Greg and Susie Zimmerman of Fairbanks saw a chickadee with a deformed bill in their yard. Theirs is the only reported sighting north of the Alaska Range. During the most recent Christmas Bird Count in Southcentral Alaska, one-third of the people with black-capped chickadees at feeders reported seeing one or more deformed birds.

"That was pretty shocking," Handel said.

Chickadees don't seem to be the only species developing bill problems. Handel said she has logged more than 60 reports of 15 other species with deformed bills, but black-capped chickadees are by far the most commonly reported. What's causing black-capped chickadees to grow beaks that are long and curved?

Handel said chickadee beaks grow a lot like fingernails, with a growing outer sheath that is usually worn down as a bird pecks at food. Something is causing the tips of chickadee beaks to become crooked, and the misalignment prevents the tips from being worn. The overgrown beaks could be the effect of a bird crashing into a window and breaking the bone beneath the beak, but Handel said she's found no evidence of impact in afflicted chickadee specimens people have brought to her lab.

A more likely culprit sweeping through the chickadee population is either an infection or exposure to a chemical pollutant. Researchers tested chickadees last year and found signs of PCBs-an industrial waste product from electronics manufacturing-in all birds, regardless of whether their beaks were deformed. The testers found very low concentrations of DDE, a byproduct of the pesticide DDT, in all of the affected birds. A research biologist, Handel now finds herself in the role of detective. She and other researchers are following several clues. Since chickadees live their entire lives within a few square miles, whatever is causing them to be disfigured must also reside in Alaska. Maybe it's birdseed from a contaminated source. Perhaps the birds have picked up insecticide from trees sprayed for bark beetles. Other possible sources of contamination are fire retardant dropped from aircraft or airborne pollutants from other continents, but these are just speculations.

This summer, several hundred volunteers will install chickadee nest boxes in their yards throughout Southcentral. Handel and her colleagues will look for deformities in newly hatched birds. They will also examine nesting chickadees for evidence of disease or contaminants that researchers didn't find last year. Handel thinks it's possible that the birds captured in the winter had cleared their system of the contaminants or disease by the time the scientists checked. More frequent tests this year might turn up the smoking gun in the mystery of the Southcentral chickadees. If you have seen any chickadees with deformed bills, Handel would like the details. Email her at colleen_handel@usgs.gov or call her at (907) 786-3418.