Avian keratin disorder (AKD) is an emerging disease among wild

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

characterized by overgrowth and deformities of

beak The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for pecking, grasping, and holding (in probing for food, eating, manipulating and ...

s. Cases were first observed among

black-capped chickadee The black-capped chickadee (''Poecile atricapillus'') is a small, nonmigratory, North American passerine bird that lives in deciduous and mixed forests. It is a member of the Paridae family (biology), family, also known as tits. It has a distin ...

s in

Alaska Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...

in the late 1990s, and it has spread rapidly since then. The cause of AKD is unknown, but may be '' Poecivirus'', a species of

virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...

within the family ''Picornaviridae'' that gained ICTV recognition in 2020.

Symptoms

In AKD, accelerated growth of the keratinized outer layer of the beak (the

rhamphotheca The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for pecking, grasping, and holding (in probing for food, eating, manipulating and ca ...

) causes elongation and crossing of the

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

s of the beak. This is debilitating and often deadly, as it obstructs the birds' ability to feed and preen themselves, with the resulting dirty and matted

plumage Plumage () is a layer of feathers that covers a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage differ between species and subspecies and may vary with age classes. Within species, there can b ...

unable to play its role in

thermoregulation Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...

. One potential secondary symptom is the formation of lesions on various other keratinized tissues. Areas affected include the skin, legs, feet, claws, and feathers. Since AKD is not yet well understood, it has not been determined whether these lesions are strictly a secondary symptom or part of a

systemic disorder A systemic disease is one that affects a number of organs and tissues, or affects the body as a whole. It differs from a localized disease, which is a disease affecting only part of the body (e.g., a mouth ulcer). Examples * Mastocytosis, incl ...

. A recent study suggests a possible connection between the avian disease Poecivirus and AKD. This study noted that all those affected with AKD also were affected with Poecivirus and suggests Poecivirus may be a possible cause of AKD.

Prevalence

Initially, AKD was reported in only two species of Alaskan bird, the

tree sparrow The Eurasian tree sparrow (''Passer montanus'') is a passerine bird in the sparrow family with a rich chestnut crown and nape and a black patch on each pure white cheek. The sexes are similarly plumaged, and young birds are a duller version o ...

and a single specimen of the

white-winged crossbill The two-barred crossbill or white-winged crossbill (''Loxia leucoptera'') is a small passerine bird in the finch family Fringillidae. It breeds in the coniferous forests of North America and the Palearctic. Taxonomy The two-barred crossbill was f ...

. While overgrown and crossed beaks have been identified in upwards of 30 species within Alaska alone, many of those have had only a handful of individuals affected. Other than black-capped chickadees, the species most affected are various

corvids Corvidae is a cosmopolitan family of oscine passerine birds that contains the crows, ravens, rooks, magpies, jackdaws, jays, treepies, choughs, and nutcrackers. In colloquial English, they are known as the crow family or corvids. Currently, 13 ...

nuthatch The nuthatches () constitute a genus, ''Sitta'', of small passerine birds belonging to the family Sittidae. Characterised by large heads, short tails, and powerful bills and feet, nuthatches advertise their territory using loud, simple songs. Mo ...

es, and

woodpecker Woodpeckers are part of the bird family (biology), family Picidae, which also includes the piculets, wrynecks and sapsuckers. Members of this family are found worldwide, except for Australia, New Guinea, New Zealand, Madagascar and the extreme ...

s. In addition, surveys of Northwestern and

American crow The American crow (''Corvus brachyrhynchos'') is a large passerine bird species of the family (biology), family Corvidae. It is a common bird found throughout much of North America. American crows are the New World counterpart to the carrion cro ...

populations have indicated the possibility of regional clusters of AKD: between 2007 and 2008, the prevalence of AKD across Alaska populations of the Northwestern Crow reached nearly 17%, and up to 36% in the

Kenai Peninsula The Kenai Peninsula ( Dena'ina: ''Yaghenen'') is a large peninsula jutting from the coast of Southcentral Alaska. The name Kenai (, ) is derived from the word "Kenaitze" or "Kenaitze Indian Tribe", the name of the Native Athabascan Alaskan tribe ...

. A 2010 study estimated that in the years between 1999 and 2008 up to 6.5% of Alaska Black-capped Chickadees had bill deformities associated with AKD.

References

{{Commons category, Avian keratin disorder Bird diseases