A Black-capped Chickadee with a beak that has grown long and crossed
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. View Media Details
- 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. View Media Details
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
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. View Media Details
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. View Media Details
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. View Media Details
Some deformed birds also have feather or skin abnormalities (Figure 10).
Sources/Usage: Public Domain. View Media Details
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
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 pages
Links Related to Beak Deformity Research
Links, videos and news articles related to beak deformity research
Below are multimedia items associated with this project.
Black-capped Chickadee with a deformed crossed beak
A Black-capped Chickadee with a beak that has grown long and crossed
Red-breasted Nuthatch with an elongated deformed beak
Female Red-breasted Nuthatch with an elongated beak. It was captured in Anchorage as part of the beak deformity research project. Avian keratin disorder (AKD) is a disease 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.
Female Red-breasted Nuthatch with an elongated beak. It was captured in Anchorage as part of the beak deformity research project. Avian keratin disorder (AKD) is a disease 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.
Boreal Chickadee with a mildly deformed beak
A Boreal Chickadee with a mildly deformed beak.
A Boreal Chickadee with a mildly deformed beak.
Black-capped Chickadee with lower elongated and upper curved beak
A Black-capped Chickadee with a severely deformed beak where the upper beak is elongated and curved down while the lower beak is elongated and straight
A Black-capped Chickadee with a severely deformed beak where the upper beak is elongated and curved down while the lower beak is elongated and straight
Black-capped Chickadee with lower elongated and upper curved beak
A Black-capped Chickadee with a severely deformed beak where the upper beak is elongated and curved down while the lower beak is elongated and straight. Avian keratin disorder (AKD) is a disease characterized by debilitating beak overgrowth and other abnormalities of keratinized tissues.
A Black-capped Chickadee with a severely deformed beak where the upper beak is elongated and curved down while the lower beak is elongated and straight. Avian keratin disorder (AKD) is a disease characterized by debilitating beak overgrowth and other abnormalities of keratinized tissues.
Black-capped chickadee captured at an Anchorage banding station
A black-capped chickadee with a normal beak captured at an Anchorage banding station.
A black-capped chickadee with a normal beak captured at an Anchorage banding station.
Black-capped Chickadee with a mildly deformed beak
A Black-capped Chickadee with an upper beak slightly longer than the lower beak. Avian keratin disorder (AKD) is a disease 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.
A Black-capped Chickadee with an upper beak slightly longer than the lower beak. Avian keratin disorder (AKD) is a disease 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.
Slate-colored Junco
A Slate-colored Junco on Middleton Island, Alaska.
A Slate-colored Junco on Middleton Island, Alaska.
Black-capped Chickadee with a deformed beak that has grown long and curved down
A Black-capped Chickadee with a beak that has grown long and curved down. Avian keratin disorder (AKD) is a disease 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.
A Black-capped Chickadee with a beak that has grown long and curved down. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with a crossed beak on a branch
Black-capped Chickadee with a crossed beak on a branch.
Black-capped Chickadee with a crossed beak on a branch.
Normal Black-capped Chickadee
Normal Black-capped Chickadee
Northwestern Crow with deformed top beak in Auke Bay, Juneau, Alaska
Northwestern Crow with deformed top beak in Auke Bay, Juneau, Alaska. Avian keratin disorder (AKD) is a disease 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.
Northwestern Crow with deformed top beak in Auke Bay, Juneau, Alaska. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with a long down-curved elongated top beak
Black-capped Chickadee with a long down-curved elongated top beak. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with a long down-curved elongated top beak. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with an elongated and decurved maxilla
Black-capped Chickadee with an elongated and decurved maxilla.
Black-capped Chickadee with an elongated and decurved maxilla.
Northwestern Crow with an elongated lower beak
Northwestern Crow with an elongated lower beak. It was captured as part of the beak deformity research project. Avian keratin disorder (AKD) is a disease 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.
Northwestern Crow with an elongated lower beak. It was captured as part of the beak deformity research project. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with elongated upper beak
Black-capped Chickadee with elongated upper beak. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with elongated upper beak. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with a long upper beak in the brush
Black-capped Chickadee with a long upper beak in the brush. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with a long upper beak in the brush. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with upper long, curved down beak and crossed
Black-capped Chickadee with upper long, curved down beak and crossed. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with upper long, curved down beak and crossed. Avian keratin disorder (AKD) is a disease 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.
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. View Media Details
- 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. View Media Details
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
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. View Media Details
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. View Media Details
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. View Media Details
Some deformed birds also have feather or skin abnormalities (Figure 10).
Sources/Usage: Public Domain. View Media Details
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
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 pages
Links Related to Beak Deformity Research
Links, videos and news articles related to beak deformity research
Below are multimedia items associated with this project.
Black-capped Chickadee with a deformed crossed beak
A Black-capped Chickadee with a beak that has grown long and crossed
A Black-capped Chickadee with a beak that has grown long and crossed
Red-breasted Nuthatch with an elongated deformed beak
Female Red-breasted Nuthatch with an elongated beak. It was captured in Anchorage as part of the beak deformity research project. Avian keratin disorder (AKD) is a disease 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.
Female Red-breasted Nuthatch with an elongated beak. It was captured in Anchorage as part of the beak deformity research project. Avian keratin disorder (AKD) is a disease 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.
Boreal Chickadee with a mildly deformed beak
A Boreal Chickadee with a mildly deformed beak.
A Boreal Chickadee with a mildly deformed beak.
Black-capped Chickadee with lower elongated and upper curved beak
A Black-capped Chickadee with a severely deformed beak where the upper beak is elongated and curved down while the lower beak is elongated and straight
A Black-capped Chickadee with a severely deformed beak where the upper beak is elongated and curved down while the lower beak is elongated and straight
Black-capped Chickadee with lower elongated and upper curved beak
A Black-capped Chickadee with a severely deformed beak where the upper beak is elongated and curved down while the lower beak is elongated and straight. Avian keratin disorder (AKD) is a disease characterized by debilitating beak overgrowth and other abnormalities of keratinized tissues.
A Black-capped Chickadee with a severely deformed beak where the upper beak is elongated and curved down while the lower beak is elongated and straight. Avian keratin disorder (AKD) is a disease characterized by debilitating beak overgrowth and other abnormalities of keratinized tissues.
Black-capped chickadee captured at an Anchorage banding station
A black-capped chickadee with a normal beak captured at an Anchorage banding station.
A black-capped chickadee with a normal beak captured at an Anchorage banding station.
Black-capped Chickadee with a mildly deformed beak
A Black-capped Chickadee with an upper beak slightly longer than the lower beak. Avian keratin disorder (AKD) is a disease 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.
A Black-capped Chickadee with an upper beak slightly longer than the lower beak. Avian keratin disorder (AKD) is a disease 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.
Slate-colored Junco
A Slate-colored Junco on Middleton Island, Alaska.
A Slate-colored Junco on Middleton Island, Alaska.
Black-capped Chickadee with a deformed beak that has grown long and curved down
A Black-capped Chickadee with a beak that has grown long and curved down. Avian keratin disorder (AKD) is a disease 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.
A Black-capped Chickadee with a beak that has grown long and curved down. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with a crossed beak on a branch
Black-capped Chickadee with a crossed beak on a branch.
Black-capped Chickadee with a crossed beak on a branch.
Normal Black-capped Chickadee
Normal Black-capped Chickadee
Northwestern Crow with deformed top beak in Auke Bay, Juneau, Alaska
Northwestern Crow with deformed top beak in Auke Bay, Juneau, Alaska. Avian keratin disorder (AKD) is a disease 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.
Northwestern Crow with deformed top beak in Auke Bay, Juneau, Alaska. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with a long down-curved elongated top beak
Black-capped Chickadee with a long down-curved elongated top beak. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with a long down-curved elongated top beak. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with an elongated and decurved maxilla
Black-capped Chickadee with an elongated and decurved maxilla.
Black-capped Chickadee with an elongated and decurved maxilla.
Northwestern Crow with an elongated lower beak
Northwestern Crow with an elongated lower beak. It was captured as part of the beak deformity research project. Avian keratin disorder (AKD) is a disease 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.
Northwestern Crow with an elongated lower beak. It was captured as part of the beak deformity research project. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with elongated upper beak
Black-capped Chickadee with elongated upper beak. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with elongated upper beak. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with a long upper beak in the brush
Black-capped Chickadee with a long upper beak in the brush. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with a long upper beak in the brush. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with upper long, curved down beak and crossed
Black-capped Chickadee with upper long, curved down beak and crossed. Avian keratin disorder (AKD) is a disease 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.
Black-capped Chickadee with upper long, curved down beak and crossed. Avian keratin disorder (AKD) is a disease 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.