The most commonly observed physical abnormalities among Alaskan birds are overgrown or crossed beaks.
Return to Ecosystems >> Terrestrial Ecosystems or Wildlife Disease and Environmental Health >> Beak Deformities >> Background of Beak Deformity Research
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. 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.
We conducted a captive study of Black-capped Chickadees 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. 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. Therefore, accelerated keratin growth appears to be the primary mechanism by which deformities develop.
In a normal Black-capped Chickadee, the upper (maxilla) and lower (mandible) parts of the beak are straight and meet at the tips.
In most affected chickadees, the maxilla (the upper) is overgrown and often curves downward. Photos show elongated and decurved maxilla on Black-capped Chickadees.
In some cases, the beak is crossed. Photo collage shows six Black-capped Chickadees with crossed beaks. Photos taken at various times.
Black-capped Chickadees with various forms of beak deformities: a) gap between upper maxilla and lower mandible; b) overgrown part of beak becomes brittle then breaks off and leaves a blunt tip; c) extremely thickened beak; and d) laterally curved beak.
Beak deformities in other species often have a similar appearance but differ slightly among groups. Deformities in woodpeckers, flickers, and nuthatches generally result from extreme overgrowth, without significant crossing or curvature.
Photos show a) Downy Woodpecker; b) Northern Flicker; and c) Red-breasted Nuthatch with beak deformities.
Most affected crows, magpies, jays, and ravens have similar growth patterns as deformed chickadees. Overgrown and downward-curving upper maxillas, severely elongated lower maxillas and mandibles, and crossed beaks are the most common corvid deformities.
Photos show American Crows and a 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; and d) Steller's Jay with longer and curved upward lower beak in La Grande, Oregon, photo courtesy of Susan Daugherty.
Other affected passerine species include Ruby-crowned Kinglet, American Robin, Varied Thrush, Orange-crowned Warbler, and others. Photos show 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 in Anchorage, Alaska, photo courtesy of Rachel Richardson.
Below are other science projects associated with this project.
Beak Deformities in Landbirds
The most commonly observed physical abnormalities among Alaskan birds are overgrown or crossed beaks.
Return to Ecosystems >> Terrestrial Ecosystems or Wildlife Disease and Environmental Health >> Beak Deformities >> Background of Beak Deformity Research
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. 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.
We conducted a captive study of Black-capped Chickadees 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. 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. Therefore, accelerated keratin growth appears to be the primary mechanism by which deformities develop.
In a normal Black-capped Chickadee, the upper (maxilla) and lower (mandible) parts of the beak are straight and meet at the tips.
In most affected chickadees, the maxilla (the upper) is overgrown and often curves downward. Photos show elongated and decurved maxilla on Black-capped Chickadees.
In some cases, the beak is crossed. Photo collage shows six Black-capped Chickadees with crossed beaks. Photos taken at various times.
Black-capped Chickadees with various forms of beak deformities: a) gap between upper maxilla and lower mandible; b) overgrown part of beak becomes brittle then breaks off and leaves a blunt tip; c) extremely thickened beak; and d) laterally curved beak.
Beak deformities in other species often have a similar appearance but differ slightly among groups. Deformities in woodpeckers, flickers, and nuthatches generally result from extreme overgrowth, without significant crossing or curvature.
Photos show a) Downy Woodpecker; b) Northern Flicker; and c) Red-breasted Nuthatch with beak deformities.
Most affected crows, magpies, jays, and ravens have similar growth patterns as deformed chickadees. Overgrown and downward-curving upper maxillas, severely elongated lower maxillas and mandibles, and crossed beaks are the most common corvid deformities.
Photos show American Crows and a 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; and d) Steller's Jay with longer and curved upward lower beak in La Grande, Oregon, photo courtesy of Susan Daugherty.
Other affected passerine species include Ruby-crowned Kinglet, American Robin, Varied Thrush, Orange-crowned Warbler, and others. Photos show 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 in Anchorage, Alaska, photo courtesy of Rachel Richardson.
Below are other science projects associated with this project.