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
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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
Background of Beak Deformity Research
Species Affected by Beak Deformities
Prevalence, Distribution and Timing of Beak Deformities in Birds
Beak Deformity's Effects on Birds
Possible Causes for Beak Deformities
Literature Cited for Beak Deformities
Links Related to Beak Deformity Research
- Overview
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
Sources/Usage: Public Domain.Figure 3. Normal Black-capped Chickadee close up.(Public domain.) - 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.
Sources/Usage: Public Domain.Figure 4. Elongated and decurved maxilla on Black-capped Chickadees.(Public domain.)
Sources/Usage: Public Domain.Figure 5. A collage of 6 Black-capped Chickadees with crossed beaks. Taken at various times. Upper right taken by Joy Geiselman, lower middle by Rachel Richardson, all by USGS, Alaska Science Center.(Public domain.)
Sources/Usage: Public Domain.Figure 6. Black-capped Chickadees with various forms of beak deformities: a) gap between maxilla and mandible; b) overgrown part of beak becomes brittle breaks off and leaves a blunt tip; c) extremely thickened beaks; and d) laterally curved beaks.(Public domain.) 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.
Sources/Usage: Public Domain.Figure 7. Downy Woodpecker, Northern Flicker and Red-breasted Nuthatch with beak deformities.(Public domain.) 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.
Sources/Usage: Public Domain.Figure 8. Northwestern Crows and Steller's Jay with beak deformities: a) crow with elongated lower beak; b) crow with elongated and curved upper beak; c) crow with longer upper beak in Seward, Alaska, photo courtesy of Charlie Finn; d) Steller's Jay with longer and curved upward lower beak in La Grande, Oregon, photo courtesy of Susan Daugherty.(Public domain.) 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.
Sources/Usage: Public Domain.Figure 9. Passerine species with beak deformities: a) Chestnut-sided Warbler in Newton Centre, Massachusetts, photo courtesy of John Neufeld; b) Yellow-rumped or Myrtle Warbler in Cape May, New Jersey, photo courtesy of John McNamara; c) Slate-colored Junco on Middleton Island, Alaska, photo courtesy of Rachel Richardson; and d) Boreal Chickadee, photo courtesy of Rachel Richardson.(Public domain.) Some deformed birds also have feather or skin abnormalities (Figure 10).
Sources/Usage: Public Domain.Figure 10. Black-capped Chickadee with scaly legs.(Public domain.) See the Multimedia tab for more examples and full size versions of all of the images in the collages above.
- Science
Below are other science projects associated with this project.
Beak Deformities in Landbirds
Over the past 20 years, Alaskans have witnessed a startling increase of beak deformities among Black-capped Chickadees and other species of resident birds. This disease, called avian keratin disorder (AKD), is characterized by debilitating beak overgrowth and other abnormalities of keratinized tissues. Affected birds have difficulty feeding and preening, and may suffer high rates of mortality.Background of Beak Deformity Research
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...Species Affected by Beak Deformities
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.Prevalence, Distribution and Timing of Beak Deformities in Birds
The rates of beak deformities documented in Black-capped Chickadees and Northwestern Crows in Alaska are the highest ever recorded within a wild bird population anywhere.Beak Deformity's Effects on Birds
Birds with beak deformities 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.Possible Causes for Beak Deformities
Beak deformities can be caused by a variety of factors, including contaminants, nutritional deficiencies, disease, parasites, blunt trauma, or genetic abnormalities. We recently identified a novel picornavirus (Poecivirus) in Black-capped Chickadees with avian keratin disorder (AKD). Our results suggest that Poecivirus is the most likely factor responsible for beak deformities in Alaskan birds...Literature Cited for Beak Deformities
Literature Cited in the Beak Deformity web pagesLinks Related to Beak Deformity Research
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