Winged Warnings: Twisted beaks
Scientists exploring mysterious deformities focus on new virus
ANCHORAGE, Alaska – Home from work, Sandra Talbot headed straight for her favorite spot, a window overlooking the bird feeder. The winter light sparkled off the snow cushioning the white spruce and birch forest around her house. She watched the commotion of songbirds, vying for the best seed or chunk of peanut butter.
Amid the pack, one stood out: a bird with a beak curved like a piece of macaroni. The black-capped chickadee looked dirty and unkempt. It couldn't preen, and it had to awkwardly tip its head to the side to pick up a piece of suet.
Talbot, a wildlife geneticist at the U.S. Geological Survey and a backyard birder, was stunned. She doubted the bird would live much longer.
"When you see one that's so deformed, you have a visceral reaction," she said. "It's hard not to have thoughts that if it's something in the chickadee's environment, it's in our environment, too."
Talbot's backyard observation on that winter day 16 years ago tipped off scientists that something was awry in the bird world, triggering a full-scale investigation into one of the most perplexing and enduring avian mysteries of recent decades.
Deformed beaks have been observed in 6.5 percent of adult chickadees captured in Alaska.
Today, deformed beaks have been discovered in more than 2,500 of Alaska's chickadees, or 6.5 percent of captured adults, and in 29 other species in south central Alaska. For crows, the disfigured beaks are even more prevalent, at 17 percent, the "highest rate of gross deformity ever documented in a wild bird population," according to the USGS. A strikingly similar condition has been discovered in other birds throughout the world, including recently in the United Kingdom.
Although they've ruled nothing out, scientists now are focusing on sequencing the genome of a mysterious virus detected in Alaska's deformed chickadees.
"We found an interesting new species of virus. It's a candidate," said University of California, San Francisco, disease ecologist Maxine Zylberberg. "If we find the virus is the immediate cause of the disease, it gives us a starting point to explore the ecological factors at play that are allowing this virus to emerge now."
Beak deformities go back decades, serving as some of the first indicators that common chemicals had ecological consequences. Shocking sights of mangled beaks in dead embryos and surviving chicks led scientists to hidden pollution sites around the country. In the Great Lakes in the 1970s, researchers linked crossed beaks and other deformities in herons, eagles and terns to industrial chemicals called polychlorinated biphenyls, or PCBs. Also, selenium poisoning in California's Central Valley caused deformities in shorebirds and waterfowl in the 1980s. Diseases and diets also have distorted bills.
But Alaska's disorder appears to be a new kind of outbreak: It doesn't show up until birds are at least six months old, at the time of sexual maturation, which suggests a novel threat. Scientists don't know if it's a latent defect, probably triggered by a pathogen or chemical, that is programmed into the embryo or if the exposure comes later in life.
Residing year-round in the state and announcing the changing seasons, chickadees are iconic birds to Alaskans.
"Something new could have emerged in birds that never has been described before," said James P. Ludwig, a field biologist who found Great Lakes birds maimed by contaminants in the 1960s. "It's going to take time to unravel this mystery."
Not a fluke
When Talbot first saw the deformed bird outside her house, she called her USGS colleague, Colleen Handel, who had been studying chickadees and other songbirds. Handel went over to the Talbot house to see it.
"At first I thought it was a bird carrying a twig in its mouth," Handel said. They clipped its beak so it would have less trouble eating. She remembers shrugging it off, thinking "these things happen."
But soon after, Handel noticed a newspaper photo shot by a reader in the Matanuska Valley, 35 miles from Anchorage, showing a chickadee with a deformed beak. The photo accompanied a writer's letter making the point that handicaps strike bird and human alike.
A USGS researcher removes a crow from a trap. USGS
"I looked at the photo," Handel said, "and thought it was really odd that there was another bird with a deformed beak. It was a red flag to me. I guess that's the serendipity of science."
Handel called local birding groups and the media asking people to be on the lookout. She was inundated with reports. The black-capped chickadee is popular with birders for its oversized rounded head, puffy shape and "feebee" whistle. Its boldness and curiosity brings it to backyard feeders. To Alaskans, chickadees are iconic birds: Curious and acrobatic, the 5-inch bird with its distinctive white cheeks and black cap and bib is a year-round resident of Alaska, and its changing calls announce the seasons. "They mean something to us like wolves and brown bears and the scent of balsam poplar in the spring," Talbot said.
With so many sightings, Handel knew the deformed beak wasn't a fluke of nature. Her team started capturing chickadees in funnel feeder traps and in mist nets, and examining and releasing them. Fortunately for the researchers, chickadees are easy to study because they generally stay in the same place once they've found a mate.
Reports of overgrown beaks in red-tailed hawks and other raptors also started coming in from the Pacific Northwest, where the nonprofit Falcon Research Group began gathering data. The USGS team hasn't confirmed the similar condition as the same disorder.
Bird beaks have intrigued scientists since Darwin noted different bird species on the Galapagos Islands based on the size and shape of their bills.
A normal chickadee beak, like the one on the right, is short and not curved.USGS
In normal chickadees, the upper and lower beaks are stubby and meet at the tips. They're adapted to pecking seeds and insects and probing tree cavities. In deformed chickadees, the upper beak is elongated and often curved downward.
Handel's team took X-rays, and discovered that the accelerated growth was occurring not in the bone beak itself but in the keratin, a layer of fibrous protein that covers the bone. It's a thick, cornified layer called the rhamphotheca, particularly adapted to foraging and containing sensory organs that detect prey.
Research wildlife biologist Caroline Van Hemert joined the USGS team, and launched a two-year study with Handel and toxicologist Todd O'Hara. They discovered that the keratin layer in deformed birds was growing at twice the rate of normal birds. Sometimes only the upper beak grew faster; other times the lower beak would also grow faster but at not so rapid a pace. Sometimes the beaks would twist and cross. If too long, they would break off, but the elongation would return in about six weeks. None of the chickadees with normal beaks died during the study. But some with the disorder died, leading the researchers to suspect a weakening effect.
Observations in the wild added to the picture of the sick birds. The affected chickadees couldn't clean their feathers, so they had trouble staying warm in winter. They couldn't feed fast enough to replace the one-tenth of their 10-gram weight lost every day.
Somehow, many lived to mate, bearing normal young and exhibiting amazing adaptations to compensate for the loss of use of their beaks. A parent with a deformed beak, for instance, would pass a bill-load of insects to a normal-beaked parent to feed the young.
Of captured crows in southeast Alaska, 17 percent had deformed beaks like this one.
Some of the affected birds have lesions in other tissues sheathed by keratin, including skin, claws and feathers.
Backyard birders haven't reported a drop in numbers of chickadees. But researchers worry that deaths connected to avian keratin disorder may be chipping away at the population. To add to the worry, they also see deformed beaks in many crows, magpies and woodpeckers.
Searching for the cause
Finding the cause has been an endurance test of checking leads, discarding some and pursuing others. Testing for chemical contaminants and infectious diseases haven't turned up any connection: There has been no elevated exposure to PCBs, dioxins, chlorinated pesticides or mercury, all chemicals known to harm birds.
Unlike the predatory birds in the Great Lakes that accumulated PCBs from fatty fish, chickadees eat insects and small seeds, which are less likely sources of chemicals. Because chickadees also come to feeders, Handel tested a variety of commercial sunflower seeds and found no harmful substances.
At first Handel suspected airborne chemicals from a wildfire northwest of Anchorage in 1996, a few years before the appearance of the deformed chickadees. But now, since the defects are turning up beyond the original location, the fire is an unlikely culprit.
Nevertheless, Handel hasn't put to rest the possibility of dioxins released during combustion of trees. "There are wildfires all over, but not the same kind of deformed beak clusters that we've got here. The question is, what's unique to Alaska?"
A researcher measures a captured chickadee's beak.Dennis McAfee
Looking for evidence of disease, Handel sent off samples to wildlife laboratories, including the University of Minnesota, where researchers used an electron microscope to search for unusual pathogens. Van Hemert studied the structure of abnormal beaks and worked with the pathologists. No bacterial, viral, fungal or parasitic infections were found.
Then John Dumbacher at the California Academy of Sciences contacted Handel after reading her papers in journals. He offered genetic techniques to detect viruses. "The disorder appeared to be spreading rapidly, and some of these sick birds were turning up in places with no known impact" of environmental toxicants, Dumbacher said.
In other research, a bornavirus causing a widespread wasting disease in parrots, macaws and cockatiels was uncovered using a gene-sequencing technique designed by professor Joseph DeRisi and his team at University of California, San Francisco. Dumbacher and DeRisi decided they also would search on the molecular level for a hidden virus in chickadees.
Zylberberg, formerly at California Academy of Sciences and now in DeRisi's laboratory, used a powerful computer capable of reading hundreds of gigabases of genetic data in a single sequencing run. She had to build a new sequence of genes by stitching together pieces that she got using the new methodology. Then she compared a new genome of a virus to existing viruses, and found that it hadn't been identified. This new virus was only 30 percent similar in its genetic code to its closest virus relative, which also is found in birds.
Half of the deformed chickadees had the virus, while only a very few healthy chickadees did. Now the next step is to grow a stock of the virus in bird cell lines, so Zylberberg can conduct experiments to understand its biology.
The new virus may cause avian keratin disorder just as the bornavirus caused the parrot's wasting disease. But Zylberberg cautioned that just because a bird has a virus doesn't mean it's causing the disorder. Birds weak from avian keratin disorder may be susceptible and pick up the virus, or weakening from the virus may leave them susceptible to the disorder.
Climate change, transformation of land use and chemicals used in various industries can lead to weakening of immune function. "Or it could be chance," she said.
Another intriguing possibility is identifying the genes that control growth of the keratin layer, then tracking down causative agents that might be driving the abnormal beak growth patterns. The hitch is that no researcher has found the key genes involved. "We first have to identify which genes are involved in the keratin growth, and then figure out what possible agents could be causing the changes. It's likely that there's some little gene that is switched on or switched off that fails to suppress or accelerates the growth of the keratinized cells in the beak," Handel said.
Scientist Caroline Van Hemert frees a bird from a mist net. Dennis McAfee
The USGS scientists in Anchorage plan to try "next generation" techniques that sort through the genetic code of individual birds with and without the keratin disorder. "There are likely to be many, many differences between the two groups, however, so it will not be an easy task to determine which are functionally related to the disorder," Handel said.
In the meantime, scientists elsewhere, particularly in the United Kingdom, wonder if several dozen other species of birds with deformed beaks are suffering from the same disorder as Alaska's chickadees.
"It's like when you're talking about cancer. There are many different kinds," Handel said. "They have similar clinical signs but they might be caused by a multitude of different factors. Until you know what's causing it or how the disorder operates, you can't say for certain that it is the same disorder."
Van Hemert untangled the black-capped chickadee from the fine mist net set in a birch forest. She was trying to free the feet first. Its upper beak jutted out grotesquely in an extravagant overbite.
She was leading the bimonthly six days of fieldwork to measure chickadees' weight, blood, age and beak length.
Van Hemert releases a chickadee.Dennis McAfee
"For something so small and delicate, they're incredibly feisty. Sometimes they try to bite to defend themselves. When they're annoyed, they raise their back head feathers," she said.
In two days of trapping, this was Van Hemert's first deformed bird. The same chickadee had been caught and examined a year earlier, based on its leg band. But back then, its beak was normal.
She worries about the birds, and hopes the mystery is soon resolved as the scientists painstakingly follow all leads. "We know what it's not. Until we know the culprit, we don't know what it is."
Twisted Beaks is the tenth installment in our Winged Warnings series. Check out the rest of the series here.