An update on fishhook chickadee beaks

An update on fishhook chickadee beaks

Over 26 years ago, my friend Ned Rozell wrote about a startling new deformity seen in Alaska's black-capped chickadees:

"In 1991, a man living in King Salmon noticed three black-capped chickadees with beaks curved like fishhooks," Rozell wrote. "Since then, hundreds of people from Southcentral Alaska have seen chickadees with overlong beaks that make it difficult for the birds to feed. The drastic increase in sightings has biologists worried that something is very wrong in Southcentral."

Since 1999, biologists with the U.S. Geological Survey's Alaska Science Center have cataloged over 3,000 reports across Alaska of so-called avian keratin disorder in black-caps, which they cite as "the highest concentration of [visible] deformities ever recorded in a wild bird population."

Normally, black-capped chickadees have a fairly short beak with a top and bottom that cleanly meet at the tip, a pointy contrast to their dark, round head and perfectly toasted-marshmallow bodies.

A diseased bird's beak grows long due to the unregulated accumulation of keratin, a tough protein that also makes up scales, hair, nails, feathers, horns and skin. Elongated beaks, which can measure up to 1.5 inches long, or nearly six times the expected length, may also dramatically curve down or crisscross.

In his column from 2000, Rozell left us with several speculations about the cause of the bizarre beaks, including chemical exposure, contaminated birdseed or altered growth after a window collision. Since his column was published, biologists have homed in on the most likely cause: a novel virus.

The scientists who discovered this virus in black-capped chickadees named it poecivirus, a nod to the species' Latin name, Poecile atricapillus. In their 2016 study, 100% of birds with avian keratin disorder carried the virus, whereas only 20% of birds with normal beaks were infected. Later work further confirmed a strong association between carrying poecivirus and beak deformation.

As Rozell noted, long, twisted beaks are not suited to pecking and preening, and affected birds appear to have higher mortality rates than healthy birds.

According to the Alaska Science Center, death rates may be highest during winter's shortest, coldest days. To survive and maintain a body temperature 150 degrees Fahrenheit above air temperature, black-capped chickadees must eat 10% of their body weight in food - seeds, dormant insects, other cached snacks - every day. Beak deformities can tip the chickadee off this knife-edge of survival.

A less obvious reason for the increased deaths is the birds' inability to keep their feathers clean and tidy. Dirty and matted feathers do not insulate as well, and affected chickadees with near-black breast feathers have been found dead near homes in the winter.

For a black-capped chickadee lover, of whom there are many in Alaska, it can be difficult to look at photos of black-caps suffering from this disease. Do we need to be worried about the future of our most charming and chattery winter songbird?

According to the Alaska Science Center, around 6.5% of adult black-capped chickadees in Alaska are affected by avian keratin disorder. Having the disease doesn't prevent egg laying, incubation and hatching, but fewer eggs hatch on average from nests where the female has a beak deformity. If the male has the deformity, fewer nestlings survive, likely due to difficulty in foraging and bringing food back to the baby birds.

While these mortality and breeding trends are concerning, black-capped chickadee populations are currently secure, according to the Alaska Department of Fish and Game.

The USGS Alaska Science Center continues to monitor the prevalence of the disease and to invest in research to understand how poecivirus contributes to beak deformities, how the virus is transmitted and its prevalence in other Alaska bird species.

Have you seen a black-capped chickadee or other bird species with a misshapen bill? You can report a beak deformity observation via the center's website: https://bit.ly/beak-deformity.

Since the late 1970s, the University of Alaska Fairbanks Geophysical Institute has provided the Alaska Science Forum column free in cooperation with the UAF research community. Sara Wilbur is a communications coordinator for the Geophysical Institute public information office.