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Black-capped Chickadee with a deformed beak at a feeder - photo by Lee Tibbitts, USGS
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 30 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 other parts of North America and Europe. 

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.  Affected 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 birds with beak deformities breed successfully, they typically encounter more challenges than normal birds.

Abnormal beaks are relatively rare among adult birds, with most published reports being of single anomalous individuals (Craves 1994).  Prevalence of beak deformities in Black-capped Chickadees and Northwestern Crows is much higher than typical background levels for a normal, wild population.  Based on reports from around the state, deformities in other Alaskan species also appear to be unusually common and warrant further investigation.

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Page Last Modified: December 6, 2016