Background

Black-capped Chickadee, photo by Lee Tibbitts

Large numbers of Black-capped Chickadees with abnormal beaks were reported in south-central Alaska in the late 1990s.  More recently, similar beak deformities have appeared in other species throughout the state. At least 29 Alaskan bird species are affected and the geographic extent of the problem appears to be growing.  In addition to Alaskan observations, we have received increasing numbers of reports from the Yukon Territory, British Columbia, and Washington State. 

The most commonly observed physical abnormalities among Alaskan birds are overgrown or crossed beaks.  The severity of the deformities varies, ranging from a nearly indiscernible “overbite” to beaks that are more than double their normal length.  The upper and lower parts of the beak are also frequently crossed or gapped.  Deformities have a variety of effects on birds.  Deformed birds often have difficulty foraging and preening, and may not be able to keep themselves warm and well-fed during cold winter months.  Although some deformed birds breed successfully, they typically encounter more challenges than normal birds.