Often-Fatal Beak Deformity in Birds May Be Due to Virus

A mystery that has baffled scientists for more than a decade might be closer to being solved.

Photo: Avian Keratin Disorder can severely impact a bird's ability to preen -- a behavior crucial to its survival. Here, a black-capped chickadee with a curved beak sits on a branch in Homer, Alaska. Credit: Martin Renner A new clue has been found in the search for the cause of a mysterious disorder that leaves some birds with horribly deformed beaks and often spells death for the animals.

The condition, avian keratin disorder (AKD), has bedeviled researchers for more than a decade, its cause remaining stubbornly hidden.

Now, in research published in the journal mBio, scientists from the California Academy of Sciences, the University of California San Francisco (UCSF), and the U.S. Geological Survey (USGS) have found a new virus they think could be the cause of the condition.

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Birds with AKD have overgrown, misshapen beaks that leave them unable to do two crucial things properly: eat and preen. With beaks that are overly long, crossed or unnaturally curved, food is more difficult for them to handle or obtain. When birds preen, meanwhile, they use their beaks to groom their feathers, rid themselves of mites and other parasites, and spread crucial waterproofing oils evenly over themselves.

"When deformed beaks restrict them from these life-giving activities, birds become cold, hungry, and often die," said Jack Dumbacher, study co-author and California Academy of Sciences curator of ornithology and mammalogy, in a statement.

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AKD was first spotted in Alaska in the 1990s and has since been reported in a number of species in the lower 48 states and Canada as well as Asia and Europe. Crows, chickadees, jays, woodpeckers, and nuthatches are its most common victims.

Previous research has looked at a number of potential causes for AKD – from bacterial or fungal infections to environmental contamination to previously known bird diseases – and come up empty.

Now, though, Dumbacher and his co-authors have discovered a potential culprit: a new virus, discovered through genetic screening for pathogens performed on bird samples from Alaska.

"This new virus is the strongest lead we've had so far as to a likely cause of the unusual cluster of beak deformities," said Caroline Van Hemert, a study co-author and a scientist with the USGS.

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The researchers have named the new virus Poecivirus, in honor of the Alaska bird used in the gene sequencing, a black-capped chicadee (Poecile atricapillus) whose species was also the first ever found with the disorder.

"We don't know if Poecivirus is causing this pathology, but we do know that this virus is not limited to chickadees," said the study's lead author Maxine Zylberberg, a UCSF researcher. She noted that while the virus was found in every chickadee with AKD they examined, it was also found in beak-deformed nuthatches and crows.

Next up, the team plans to study how AKD is transmitted, including nailing down definitively that it's caused by the newfound Poecivirus.

"More work is needed to determine if Poecivirus is causing AKD, but the evidence suggests that it is a strong candidate," said Zylberberg.