Physical Description of Beak Deformities
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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.
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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.
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.)
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.
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.
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.
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).
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...
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Date published: August 21, 2018Status: Active
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...
Attribution: Region 11: Alaska, Alaska Science Center -
Date published: August 20, 2018Status: Active
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.
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Date published: August 18, 2018Status: Active
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.
Attribution: Region 11: Alaska, Alaska Science Center -
Date published: August 17, 2018Status: Active
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.
Attribution: Region 11: Alaska, Alaska Science Center -
Date published: August 16, 2018Status: Active
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...
Attribution: Region 11: Alaska, Alaska Science Center -
Date published: August 15, 2018Status: Active
Literature Cited for Beak Deformities
Literature Cited in the Beak Deformity web pages
Attribution: Region 11: Alaska, Alaska Science Center -
Date published: August 14, 2018Status: Active
Links Related to Beak Deformity Research
Links, videos and news articles related to beak deformity research
Attribution: Region 11: Alaska, Alaska Science Center
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.
Avian keratin disorder of Alaska black-capped chickadees is associated with Poecivirus infection
BackgroundAvian keratin disorder (AKD) is an epizootic of debilitating beak deformities, first documented in black-capped chickadees (Poecile atricapillus) in Alaska during the late 1990s. Similar deformities have now been recorded in dozens of species of birds across multiple continents. Despite this, the etiology of AKD has remained elusive,...
Zylberberg, Maxine; Van Hemert, Caroline R.; Handel, Colleen M.; DeRisi, Joseph L.Novel picornavirus associated with avian keratin disorder in Alaskan birds
Avian keratin disorder (AKD), characterized by debilitating overgrowth of the avian beak, was first documented in black-capped chickadees (Poecile atricapillus) in Alaska. Subsequently, similar deformities have appeared in numerous species across continents. Despite the widespread distribution of this emerging pathology, the cause of AKD remains...
Zylberberg, Maxine; Van Hemert, Caroline R.; Dumbacher, John P.; Handel, Colleen M.; Tihan, Tarik; DeRisi, Joseph L.Blood serum chemistry of wild Alaskan Black-capped Chickadees (Poecile atricapillus) with avian keratin disorder
We measured serum chemistries in wild Black-capped Chickadees (Poecile atricapillus) from Alaska to test for potential differences associated with beak deformities characteristic of avian keratin disorder. Lower uric acid in affected birds was the only difference detected between groups, although sample sizes were small. This difference could be...
Van Hemert, Caroline R.; Handel, Colleen M.Elements in whole blood of Northwestern Crows (Corvus caurinus) in Alaska: No evidence for an association with beak deformities
A recent outbreak of beak deformities among resident birds in Alaska has raised concern about environmental contamination as a possible underlying factor. We measured whole blood concentrations of 30 essential and nonessential elements to determine whether any were associated with beak deformities in Northwestern Crows (Corvus caurinus). We tested...
Van Hemert, Caroline R.; Handel, Colleen M.Avian malaria in a boreal resident species: long-term temporal variability, and increased prevalence in birds with avian keratin disorder
The prevalence of vector-borne parasitic diseases is widely influenced by biological and ecological factors. Environmental conditions such as temperature and precipitation can have a marked effect on haemosporidian parasites (Plasmodium spp.) that cause malaria and those that cause other malaria-like diseases in birds. However, there have...
Wilkinson, Laura C.; Handel, Colleen M.; Van Hemert, Caroline R.; Loiseau, Claire; Sehgal, Ravinder N. M.Isolation of a complete circular virus genome sequence from an Alaskan black-capped chickadee (Poecile atricapillus) gastrointestinal tract sample.
We report here the genome sequence of a circular virus isolated from samples of an Alaskan black-capped chickadee (Poecile atricapillus) gastrointestinal tract. The genome is 2,152 bp in length and is most similar (30 to 44.5% amino acid identity) to the genome sequences of other single-stranded DNA (ssDNA) circular viruses belonging to the...
Hanna, Zachary R.; Runckel, Charles; Fuchs, Jerome; DeRisi, Joseph L.; Mindell, David P.; Van Hemert, Caroline R.; Handel, Colleen M.; Dumbacher, John P.Environmental contaminants and chromosomal damage associated with beak deformities in a resident North American passerine
A large cluster of beak abnormalities among black-capped chickadees (Poecile atricapillus) in Alaska raised concern about underlying environmental factors in this region. Metals and trace elements, organochlorine pesticides, polychlorinated biphenyls (PCBs), and polychlorinated dibenzo-dioxins and polychlorinated dibenzofurans (PCDD-Fs) were...
Handel, Colleen M.; Van Hemert, Caroline R.Macroscopic, histologic, and ultrastructural lesions associated with avian keratin disorder in Black-capped Chickadees (Poecile atricapillus)
An epizootic of beak abnormalities (avian keratin disorder) was recently detected among wild birds in Alaska. Here we describe the gross, histologic, and ultrastructural features of the disease in 30 affected adult black-capped chickadees (Poecile atricapillus). Grossly, there was elongation of the rhamphotheca, with varying degrees of lateral...
Van Hemert, Caroline R.; Armién, A. G.; Blake, J.E.; Handel, Colleen M.; O'Hara, T. M.Stable isotopes identify dietary changes associated with beak deformities in Black-Capped Chickadees (Poecile atricapillus)
A large number of beak deformities of unknown etiology have recently been reported in Black-capped Chickadees (Poecile atricapillus) and other resident avian species in Alaska. We investigated the potential association between diet and beak deformities. We analyzed carbon (δ13C) and nitrogen (δ15N) isotopes in whole blood of Black-capped...
Van Hemert, Caroline R.; Handel, Colleen M.; O'Brien, Diane M.Evidence of accelerated beak growth associated with avian keratin disorder in black-capped chickadees (Poecile atricapillus)
We recently documented an epizootic of beak deformities in more than 2,000 Black-capped Chickadees (Poecile atricapillus) and other wild bird species in North America. This emerging avian disease, which has been termed avian keratin disorder, results in gross overgrowth of the rhamphotheca, the outer, keratinized layer of the beak. To test the...
Van Hemert, Caroline R.; Handel, Colleen M.; O'Hara, Todd M.Microanatomy of passerine hard-cornified tissues: Beak and claw structure of the black-capped chickadee (Poecile atricapillus)
The microanatomy of healthy beaks and claws in passerine birds has not been well described in the literature, despite the importance of these structures in avian life. Histological processing of hard‐cornified tissues is notoriously challenging and only a few reports on effective techniques have been published. An emerging epizootic of beak...
Van Hemert, Caroline R.; Handel, Colleen M.; Blake, John E.; Swor, Rhonda; O'Hara, Todd M.A natural experiment on the condition-dependence of achromatic plumage reflectance in black-capped chickadees
Honest advertisement models posit that only individuals in good health can produce and/or maintain ornamental traits. Even though disease has profound effects on condition, few studies have experimentally tested its effects on trait expression and even fewer have identified a mechanistic basis for these effects. Recent evidence suggests that black...
D'Alba, L.; Van Hemert, Caroline R.; Handel, Colleen M.; Shawkey, M.D.Below are multimedia items associated with this project.
Steller's Jay with deformed beak at a bird feeder
A Steller's Jay with a deformed beak at a bird feeder. This photo was from an observation report of the Alaska Science Center's Beak Deformity project.
Chestnut-sided Warbler with deformed beak
A Chestnut-sided Warbler with an unusually long beak sitting in a tree. This photo was from an observation report of the Alaska Science Center's Beak Deformity project.
Northern Flicker with a grossly crossed beak at a suet block
Northern Flicker with a grossly crossed beak hanging from a suet block. This photo was from an observation report of the Alaska Science Center's Beak Deformity project.
Northern Flicker with a grossly crossed beak in a tree
Northern Flicker with a grossly crossed beak sitting in a tree. This photo was from an observation report of the Alaska Science Center's Beak Deformity project.
Northern Flicker with a grossly crossed beak
Northern Flicker with a grossly crossed beak. This photo was from an observation report of the Alaska Science Center's Beak Deformity project.
Northern Flicker with a grossly crossed beak in the grass
Northern Flicker with a grossly crossed beak in the grass. This photo was from an observation report of the Alaska Science Center's Beak Deformity 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.
Black-Capped Chickadee with Beak Deformity
Typical beak deformity in a (Poecile atricapillus) affected by avian keratin disorder in Anchorage, Alaska
Boreal Chickadee with a mildly deformed beak
A Boreal Chickadee with a mildly deformed beak.
Steller's Jay with lower beak longer than upper beak
A Steller's Jay with a deformed beak, the bottom being longer than the top. This photo was from an observation report of the Alaska Science Center's Beak Deformity project.
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