Species Affected by Beak Deformities

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Black-capped Chickadees

Chickadees are resident throughout Alaska and other parts of their range and are generally associated with deciduous or deciduous/coniferous forests.  They are primarily cavity nesters, excavating holes in rotten wood of softwood trees (Smith 1991) and have several adaptations for surviving the extreme cold and short photoperiod characteristic of winter at high latitudes.  Chickadees often enter a state of regulated hypothermia at night (Chaplin 1974, 1976; Sharbaugh 2001), store and metabolize large amounts of fat daily (Chaplin 1974), and have a well developed spatial memory to relocate cached food (Hitchcock and Sherry 1990, Pravosudov and Lucas 2000, Pravosudov and Clayton 2002).

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Large numbers of Black-capped Chickadees with beak deformities were first reported in the late 1990s and biologists at the USGS Alaska Science Center began research in 1999.  With help from the public, we have documented over 3,000 affected Black-capped Chickadees in Alaska (Figure 1).  The first Black-capped Chickadees with beak deformities were observed in winter 1991-1992.  That winter, single chickadees with elongated beaks were seen in King Salmon and Naknek in the Bristol Bay region and in Wasilla and near Nancy Lakes in the Mat-Su Valley.

In southcentral Alaska, approximately 7% of adult black-capped chickadees are affected, which is an unusually high prevalence of deformities in a wild bird population.

By comparison, few responses from outside of Alaska have been received from inquiries through Project FeederWatch, bulletin boards, and response to national media coverage.  Although they are year-round residents across forested regions of Canada and the northern two-thirds of the contiguous United States, only scattered reports of Black-capped Chickadees with deformed beaks have been documented from outside of Alaska.

Northwestern Crows and Other Corvids

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We conducted a study on Northwestern Crows in southcentral and southeastern Alaska and estimated prevalence of beak deformities to be approximately 17%, the highest rate of gross deformity ever documented in a wild bird population! The total number of affected individuals for this species is second only to that of Black-capped Chickadees. Crows with beak deformities have been reported in south-central Alaska and along the coast to southeast Alaska, British Columbia, and Puget Sound in Washington State (see map; Figure 2). We have been soliciting reports from the public in Alaska, British Columbia, and Washington State and this information helps us to determine the number of birds affected and the geographic scope of these deformities.

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Although we have not yet conducted detailed studies of avian keratin disorder (AKD) among other corvids (the family of birds that includes crows, ravens, jays, and magpies), the frequency of deformity sightings among Common Ravens, Black-billed Magpies, and Steller's Jays suggests that prevalence is higher than normal background level for these species.

Corvids overlap geographically with Black-capped Chickadees, but there are significant differences in habitats used, particularly among Northwestern Crows.  Unlike insect- and seed-eating chickadees, crows normally feed in the intertidal zone on mussels and other filter feeders.  Presence of deformities in this species indicates that factors contributing to beak abnormalities occur across a diverse ecological gradient.

Although we have not yet determined the prevalence of beak deformities among other corvids (the family of birds that includes crows, ravens, jays, and magpies), more than 100 individuals have been documented in Alaska. The frequency of deformity sightings among Common Ravens, Black-billed Magpies, and Steller's Jays suggests that prevalence is higher than normal background level for these species.

Although corvids overlap geographically with Black-capped Chickadees within the same broad region, there are significant differences in habitats used, particularly among Northwestern Crows.  Unlike insect- and seed-eating chickadees, crows normally feed in the intertidal zone on mussels and other filter feeders.  Presence of deformities in this species indicates that factors contributing to beak abnormalities occur in both terrestrial and marine/intertidal systems.

Other Species

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In addition to Black-capped Chickadees and Northwestern Crows, at least two dozen other species have been documented with AKD in Alaska.  Most affected species are year-round residents of Alaska. Black-capped Chickadees have been the most commonly reported, followed by Northwestern Crows, Red-breasted Nuthatches, Black-billed Magpies, Steller’s Jays, and Downy Woodpeckers. Despite their use of habitats similar to nuthatches, woodpeckers, and Black-capped Chickadees, very few Boreal Chickadees and Chestnut-backed Chickadees have been reported with beak deformities.

Among migratory species, relatively few individuals have been documented with AKD in Alaska.  Among these, nearly all were juvenile birds captured or observed during autumn, meaning that they had been produced in the state.  Therefore, we assume that these individuals developed beak deformities while in Alaska and before leaving for wintering areas.

Beak deformities have also been recorded sporadically from waterbirds and raptors, including one Pacific Loon seen near Sitka, one Black-legged Kittiwake near Cordova, two adult Bald Eagles on the Kenai Peninsula, and one nestling Peregrine Falcon on the Colville River in northern Alaska. However, it’s unclear if such deformities are related to those observed in chickadees and crows.

Reports of beak deformities in the broader Pacific Northwest region have also increased in recent years.  Many of these deformities appear to be similar to those that occur in Alaskan birds, suggesting that a large geographic is affected.  The most commonly reported species from the Pacific Northwest include Red-tailed Hawks, Northwestern Crows, Northern Flickers, and Steller’s Jays.   A cluster of Red-tailed Hawks with beak deformities in Puget Sound is currently being investigated. Determining whether a single cause is responsible for beak deformities in multiple species and across a broad geographic area will provide important information about AKD and its occurrence in wild bird populations.