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.
Return to Ecosystems >> Terrestrial Ecosystems or Wildlife Disease and Environmental Health >> Beak Deformities >> Background of Beak Deformity Research
- Beak Deformity and Banded Bird Observation Report
- Beak Deformity Home
- Background
- Species Affected
- Physical Description
- Prevalence, Distribution and Timing
- Effects on Birds
- Possible Causes
- Photo Gallery - see the Multimedia tab
- Publications - see the Publications tab
- Links
- Landbirds
In a normal Black-capped Chickadee, the upper (maxilla) and lower (mandible) parts of the beak are straight and meet at the tips (Figure 3). In most affected chickadees, the maxilla is overgrown and often curves downward (Figure 4). In some cases, the beak is crossed (Figure 5) or shows a gap between the maxilla and mandible (Figure 6a). The overgrown part of the beak may be thin and brittle and sometimes breaks off, leaving a blunt tip (Figure 6b). Other birds have extremely thickened (Figure 6c) or laterally curved (Figure 6d) beaks. The deformities appear to result from overgrowth of the rhamphotheca, the outer surface of the beak which is made of keratin. Like human fingernails, the rhamphotheca grows throughout a bird’s life and is constantly worn down through pecking and feeding. X-rays of affected birds indicated that neither the cranium nor the underlying bones of the beak itself were malformed.
We conducted a captive study of Black-capped Chickadee to measure rates of beak growth in birds with AKD. We found that the beaks of affected birds grew, on average, twice as fast as those of birds with apparently normal beaks. Therefore, accelerated keratin growth appears to be the primary mechanism by which deformities develop.
Beak deformities in other species often have a similar appearance, but differ slightly among groups. Deformities in woodpeckers, flickers, and nuthatches (Figure 7a-c) generally result from extreme overgrowth, without significant crossing or curvature.
Most affected crows (Figure 8), magpies, jays (also Figure 8), and ravens, have similar growth patterns as deformed chickadees. Overgrown and downward-curving maxillas, severely elongated maxillas and mandibles, and crossed beaks are the most common corvid deformities.
Other affected passerine species, including Ruby-crowned Kinglet, American Robin, Varied Thrush, Orange-crowned, Chestnut-sided (Figure 9a) and Yellow-rumped (Myrtle) warblers (Figure 9b), Savannah and Lincoln’s sparrows, Dark-eyed and Slate-colored Junco (Figure 9c), Pine Grosbeak, Common Redpoll, Boreal Chickadee (Figure 9d), and Pine Siskin, typically exhibit beaks with crossed tips and/or varying amounts of overgrowth.
Some deformed birds also have feather or skin abnormalities (Figure 10).
See the Multimedia tab for more examples and full size versions of all of the images in the collages above.
Below are other science projects associated with this project.
Beak Deformities in Landbirds
Below are multimedia items associated with this project.
Below are publications associated with this project.
Handel, C. M., L. M. Pajot, S. M. Matsuoka, K. A. Trust, J. M. Stotts, J. Terenzi, and S. L. Talbot. 2006. Potential Role of Environmental Contaminants in the Pathology of Beak Deformities among Black-capped Chickadees in South-central Alaska. Unpb. final rpt. Project ID: 1130-7F22. U. S. Geological Survey, Alaska Science Center, Anchorage, AK.
Beak deformities in Northwestern Crows: Evidence of a multispecies epizootic
Epizootic of beak deformities among wild birds in Alaska: An emerging disease in North America?
Alaskan birds at risk: Widespread beak deformities in resident species
Use of buccal swabs for sampling DNA from nestling and adult birds
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.
Return to Ecosystems >> Terrestrial Ecosystems or Wildlife Disease and Environmental Health >> Beak Deformities >> Background of Beak Deformity Research
- Beak Deformity and Banded Bird Observation Report
- Beak Deformity Home
- Background
- Species Affected
- Physical Description
- Prevalence, Distribution and Timing
- Effects on Birds
- Possible Causes
- Photo Gallery - see the Multimedia tab
- Publications - see the Publications tab
- Links
- Landbirds
In a normal Black-capped Chickadee, the upper (maxilla) and lower (mandible) parts of the beak are straight and meet at the tips (Figure 3). In most affected chickadees, the maxilla is overgrown and often curves downward (Figure 4). In some cases, the beak is crossed (Figure 5) or shows a gap between the maxilla and mandible (Figure 6a). The overgrown part of the beak may be thin and brittle and sometimes breaks off, leaving a blunt tip (Figure 6b). Other birds have extremely thickened (Figure 6c) or laterally curved (Figure 6d) beaks. The deformities appear to result from overgrowth of the rhamphotheca, the outer surface of the beak which is made of keratin. Like human fingernails, the rhamphotheca grows throughout a bird’s life and is constantly worn down through pecking and feeding. X-rays of affected birds indicated that neither the cranium nor the underlying bones of the beak itself were malformed.
We conducted a captive study of Black-capped Chickadee to measure rates of beak growth in birds with AKD. We found that the beaks of affected birds grew, on average, twice as fast as those of birds with apparently normal beaks. Therefore, accelerated keratin growth appears to be the primary mechanism by which deformities develop.
Beak deformities in other species often have a similar appearance, but differ slightly among groups. Deformities in woodpeckers, flickers, and nuthatches (Figure 7a-c) generally result from extreme overgrowth, without significant crossing or curvature.
Most affected crows (Figure 8), magpies, jays (also Figure 8), and ravens, have similar growth patterns as deformed chickadees. Overgrown and downward-curving maxillas, severely elongated maxillas and mandibles, and crossed beaks are the most common corvid deformities.
Other affected passerine species, including Ruby-crowned Kinglet, American Robin, Varied Thrush, Orange-crowned, Chestnut-sided (Figure 9a) and Yellow-rumped (Myrtle) warblers (Figure 9b), Savannah and Lincoln’s sparrows, Dark-eyed and Slate-colored Junco (Figure 9c), Pine Grosbeak, Common Redpoll, Boreal Chickadee (Figure 9d), and Pine Siskin, typically exhibit beaks with crossed tips and/or varying amounts of overgrowth.
Some deformed birds also have feather or skin abnormalities (Figure 10).
See the Multimedia tab for more examples and full size versions of all of the images in the collages above.
Below are other science projects associated with this project.
Beak Deformities in Landbirds
Below are multimedia items associated with this project.
Below are publications associated with this project.
Handel, C. M., L. M. Pajot, S. M. Matsuoka, K. A. Trust, J. M. Stotts, J. Terenzi, and S. L. Talbot. 2006. Potential Role of Environmental Contaminants in the Pathology of Beak Deformities among Black-capped Chickadees in South-central Alaska. Unpb. final rpt. Project ID: 1130-7F22. U. S. Geological Survey, Alaska Science Center, Anchorage, AK.