Biologist Colleen Handel saw her first black-capped chickadee with the heartrending disorder in 1998.
The tiny birds showed up at birdfeeders in Alaska's largest city with freakishly long beaks. Some beaks looked like sprung scissors, unable to come together at the tips. Others curved up or down like crossed sickles.
Handel, a U.S. Geological Survey bird specialist, was sure the cause of avian keratin disorder would be found quickly: contaminated birdseed, a poison targeting spruce bark beetles, maybe some sort of bacterium or fungus.
Years went by. She found herself losing sleep over a mysterious ailment afflicting 6.5 percent of southcentral Alaska's black-capped...