Black-capped Chickadee with a deformed crossed beak
Black-capped Chickadee with a deformed crossed beakA Black-capped Chickadee with a beak that has grown long and crossed
Prevalence, Distribution and Timing of Beak Deformities in Birds
Active
By Alaska Science Center
February 26, 2025
The rates of beak deformities documented in Black-capped Chickadees and American Crows in Alaska are the highest ever recorded within a wild bird population anywhere.
Since the 1990's, prevalence of avian keratin disorder (AKD) has clearly increased in Alaska and now affects an estimated 6.5% (±0.5%) of adult Black-capped Chickadees and 16.9% (±5.3%) of adult American Crows.
Typically, abnormal beaks are relatively rare among adult birds, and background levels are less than 0.5% in normal populations. The prevalence we measured in chickadees was four times higher than the maximum rate previously documented for any passerine (Pomerory 1962). For crows, this estimate was more than 15 times higher.
Based on reports from the late 1990s, two epicenters of AKD among Black-capped Chickadees were first identified: one in the Mat-Su Valley and one in Bristol Bay. Beak deformities initially appeared to be clustered in south-central Alaska, where most chickadees with beak deformities have been observed. However, relatively large numbers of chickadees and other species have recently been observed with deformities in the Fairbanks area of central Alaska. We have also documented chickadees with beak deformities at remote locations in south-central Alaska.
Beak deformities among other species, including crows, appear to be increasing in Alaska and throughout the Pacific Northwest. In addition, recent reports from other parts of North America and Europe, particularly the United Kingdom, suggest that this problem may affect a large geographic area.
Developmentally, birds appear to develop beak deformities as adults, rather than as embryos or nestlings, suggesting that they are not congenital in nature. Very few young birds had obvious deformities, as compared to high rates in adults. Most deformities were very subtle in onset, however, with slight overgrowth or asymmetry of the beak. Based on results from our winter banding study, there seems to be a higher probability of deformities developing during late winter than during other parts of the year.
Sources/Usage: Public Domain. View Media Details
Below are other science projects associated with this project.
Beak Deformities in Landbirds
Over the past 26 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. If...
Links Related to Beak Deformity Research
Links, videos, and news articles related to beak deformity research.
Possible Causes of Beak Deformities
Beak deformities can be caused by a variety of factors, including contaminants, nutritional deficiencies, disease, parasites, blunt trauma, or genetic abnormalities. In 2016, we 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
Physical Description of Beak Deformities
The most commonly observed physical abnormalities among Alaskan birds are overgrown or crossed beaks.
Effects of Beak Deformities 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.
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 by beak deformities 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.
Below are multimedia items associated with this project.
Black-capped Chickadee with a deformed crossed beak
Black-capped Chickadee with a deformed crossed beak
Black-capped Chickadee with a deformed crossed beakA Black-capped Chickadee with a beak that has grown long and crossed
Boreal Chickadee with a mildly deformed beak
A Boreal Chickadee with a mildly deformed beak.
A Boreal Chickadee with a mildly deformed beak.
A Red-breasted Nuthatch captured at an Anchorage banding station
A Red-breasted Nuthatch captured at an Anchorage banding stationA Red-breasted Nuthatch captured at an Anchorage banding station
A Red-breasted Nuthatch captured at an Anchorage banding station
A Red-breasted Nuthatch captured at an Anchorage banding stationA Red-breasted Nuthatch captured at an Anchorage banding station
Black-capped Chickadee with lower elongated and upper curved beak
Black-capped Chickadee with lower elongated and upper curved beakA 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. Over the past 26 years, Alaskans have witnessed a startling increase of beak deformities among Black-capped Chickadees and other species of resident birds.
Black-capped Chickadee with lower elongated and upper curved beak
Black-capped Chickadee with lower elongated and upper curved beakA 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. Over the past 26 years, Alaskans have witnessed a startling increase of beak deformities among Black-capped Chickadees and other species of resident birds.
Black-capped Chickadee with lower elongated and upper curved beak
Black-capped Chickadee with lower elongated and upper curved beakA 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
Black-capped Chickadee with lower elongated and upper curved beakA 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 a mildly deformed beak
Black-capped Chickadee with a mildly deformed beakA 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.
Black-capped Chickadee with a mildly deformed beak
Black-capped Chickadee with a mildly deformed beakA 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.
Black-capped Chickadee captured at an Anchorage banding station
Black-capped Chickadee captured at an Anchorage banding stationA Black-capped Chickadee with a normal beak captured at an Anchorage banding station.
Black-capped Chickadee captured at an Anchorage banding station
Black-capped Chickadee captured at an Anchorage banding stationA Black-capped Chickadee with a normal beak captured at an Anchorage banding station.
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
Black-capped Chickadee with a deformed beak that has grown long and curved downA 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 deformed beak that has grown long and curved down
Black-capped Chickadee with a deformed beak that has grown long and curved downA 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 branchBlack-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 branchBlack-capped Chickadee with a crossed beak on a branch.
Normal Black-capped Chickadee
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, AlaskaNorthwestern 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
Northwestern Crow with deformed top beak in Auke Bay, Juneau, AlaskaNorthwestern 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 beakBlack-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
Black-capped Chickadee with a long down-curved elongated top beakBlack-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 maxillaBlack-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 maxillaBlack-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 upper long, curved down beak and crossed
Black-capped Chickadee with upper long, curved down beak and crossedBlack-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
Black-capped Chickadee with upper long, curved down beak and crossedBlack-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 rates of beak deformities documented in Black-capped Chickadees and American Crows in Alaska are the highest ever recorded within a wild bird population anywhere.
Since the 1990's, prevalence of avian keratin disorder (AKD) has clearly increased in Alaska and now affects an estimated 6.5% (±0.5%) of adult Black-capped Chickadees and 16.9% (±5.3%) of adult American Crows.
Typically, abnormal beaks are relatively rare among adult birds, and background levels are less than 0.5% in normal populations. The prevalence we measured in chickadees was four times higher than the maximum rate previously documented for any passerine (Pomerory 1962). For crows, this estimate was more than 15 times higher.
Based on reports from the late 1990s, two epicenters of AKD among Black-capped Chickadees were first identified: one in the Mat-Su Valley and one in Bristol Bay. Beak deformities initially appeared to be clustered in south-central Alaska, where most chickadees with beak deformities have been observed. However, relatively large numbers of chickadees and other species have recently been observed with deformities in the Fairbanks area of central Alaska. We have also documented chickadees with beak deformities at remote locations in south-central Alaska.
Beak deformities among other species, including crows, appear to be increasing in Alaska and throughout the Pacific Northwest. In addition, recent reports from other parts of North America and Europe, particularly the United Kingdom, suggest that this problem may affect a large geographic area.
Developmentally, birds appear to develop beak deformities as adults, rather than as embryos or nestlings, suggesting that they are not congenital in nature. Very few young birds had obvious deformities, as compared to high rates in adults. Most deformities were very subtle in onset, however, with slight overgrowth or asymmetry of the beak. Based on results from our winter banding study, there seems to be a higher probability of deformities developing during late winter than during other parts of the year.
Sources/Usage: Public Domain. View Media Details
Below are other science projects associated with this project.
Beak Deformities in Landbirds
Over the past 26 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. If...
Links Related to Beak Deformity Research
Links, videos, and news articles related to beak deformity research.
Possible Causes of Beak Deformities
Beak deformities can be caused by a variety of factors, including contaminants, nutritional deficiencies, disease, parasites, blunt trauma, or genetic abnormalities. In 2016, we 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
Physical Description of Beak Deformities
The most commonly observed physical abnormalities among Alaskan birds are overgrown or crossed beaks.
Effects of Beak Deformities 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.
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 by beak deformities 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.
Below are multimedia items associated with this project.
Black-capped Chickadee with a deformed crossed beak
Black-capped Chickadee with a deformed crossed beakA Black-capped Chickadee with a beak that has grown long and crossed
Black-capped Chickadee with a deformed crossed beak
Black-capped Chickadee with a deformed crossed beakA Black-capped Chickadee with a beak that has grown long and crossed
Boreal Chickadee with a mildly deformed beak
A Boreal Chickadee with a mildly deformed beak.
A Boreal Chickadee with a mildly deformed beak.
A Red-breasted Nuthatch captured at an Anchorage banding station
A Red-breasted Nuthatch captured at an Anchorage banding stationA Red-breasted Nuthatch captured at an Anchorage banding station
A Red-breasted Nuthatch captured at an Anchorage banding station
A Red-breasted Nuthatch captured at an Anchorage banding stationA Red-breasted Nuthatch captured at an Anchorage banding station
Black-capped Chickadee with lower elongated and upper curved beak
Black-capped Chickadee with lower elongated and upper curved beakA 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. Over the past 26 years, Alaskans have witnessed a startling increase of beak deformities among Black-capped Chickadees and other species of resident birds.
Black-capped Chickadee with lower elongated and upper curved beak
Black-capped Chickadee with lower elongated and upper curved beakA 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. Over the past 26 years, Alaskans have witnessed a startling increase of beak deformities among Black-capped Chickadees and other species of resident birds.
Black-capped Chickadee with lower elongated and upper curved beak
Black-capped Chickadee with lower elongated and upper curved beakA 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
Black-capped Chickadee with lower elongated and upper curved beakA 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 a mildly deformed beak
Black-capped Chickadee with a mildly deformed beakA 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.
Black-capped Chickadee with a mildly deformed beak
Black-capped Chickadee with a mildly deformed beakA 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.
Black-capped Chickadee captured at an Anchorage banding station
Black-capped Chickadee captured at an Anchorage banding stationA Black-capped Chickadee with a normal beak captured at an Anchorage banding station.
Black-capped Chickadee captured at an Anchorage banding station
Black-capped Chickadee captured at an Anchorage banding stationA Black-capped Chickadee with a normal beak captured at an Anchorage banding station.
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
Black-capped Chickadee with a deformed beak that has grown long and curved downA 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 deformed beak that has grown long and curved down
Black-capped Chickadee with a deformed beak that has grown long and curved downA 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 branchBlack-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 branchBlack-capped Chickadee with a crossed beak on a branch.
Normal Black-capped Chickadee
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, AlaskaNorthwestern 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
Northwestern Crow with deformed top beak in Auke Bay, Juneau, AlaskaNorthwestern 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 beakBlack-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
Black-capped Chickadee with a long down-curved elongated top beakBlack-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 maxillaBlack-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 maxillaBlack-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 upper long, curved down beak and crossed
Black-capped Chickadee with upper long, curved down beak and crossedBlack-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
Black-capped Chickadee with upper long, curved down beak and crossedBlack-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.