Avid bird watchers in Southcentral Alaska may be familiar with black-capped chickadees with deformed bills, and those that aren't soon may be because the number of birds affected appears to be on the rise.
"The deformed birds were first observed in 1991, but since then more than 1,300 affected chickadees have been reported in Alaska, representing more than 1,000 individual birds," said Colleen Handel, a research wildlife biologist with the USGS Alaska Science Center in Anchorage.
"By comparison, only 10 black-capped chickadees were reported throughout the rest of North America during the same time period," she added.
These small passerines range throughout most of sub-arctic Alaska, Canada, and in the Lower 48 can be found as far south as Texas and as far east as North Carolina and Tennessee.
Black-capped chickadees aren't the only birds to suffer the strange deformity, according to Handel.
"We have records of 150 other birds (with deformed bills) in 25 species from Southcentral Alaska," Handel said.
Photo by Joseph Robertia
Chickadee with normal beak stops at an area bird feeder.
Photo by Joseph Robertia
These include not just the song birds, but downy and hairy woodpeckers, a peregrine falcon, and most recently a bald eagle in Kenai.
The beaks of normal birds are short and stubby, but the bill deformities can range from hardly noticeable to grotesquely overgrown. It can be bill's top or bottom mandible that is affected, or sometimes both. The abnormal bill will be elongated and curved sharply back toward the body.
These unusual bill shapes inhibit the natural behavior of chickadees in a number of ways. These birds may have trouble feeding on seed since they can't crack the shells. They may resort to twisting their heads to feed, relying on hulled seed, shaved suet or peanut butter.
Birds with longer than average bills may also appear unkempt because they can not properly preen their feathers. Since birds rely on their plumage for insulation in the winter, birds with poor feather condition are probably more susceptible to illness and even death during cold winter nights.
Unfortunately, scientists still haven't been able to pinpoint the cause of the deformities.
"Several tests have been done on seed to check for contaminants, but these all came back clean," Handel said.
She said other tests for viruses and mites that can cause this type of deformities came back negative.
Even tissue samples taken to check for lindane, a chemical used to spray for spruce beetle, came back clean.
However, in other tests conducted on adult birds, juveniles and eggs, low concentrations of PCBs (poly chlorinated biphenyls) were present. DDE, a major breakdown product of DDT, was also found in the birds.
"This is no smoking gun," according to Handel. "We don't know if they're related. Nothing is for sure yet. We still need to conduct further testing of these and other chemicals."
The only thing they do know for sure is that all of the deformed birds have been found to have genetic damage to their DNA. Unfortunately, the source of this damage is still unclear.
"Bill deformities can be caused by a lot of things," Handel said.
Another oddity to the case is that the deformities seem to occur developmentally -- in other words, later in the bird's life cycle.
Handel has looked at several hundred nest boxes and has found no definitive signs of the deformities in chicks. However, many of these chicks were banded and upon recapture months later had developed the long beaks. The youngest bird so far recorded with the anomaly was six months old.
In the future Handel hopes to continue testing to determine the cause of the problem. She will be looking at investigating possible nutritional inhibitors that could cause metabolic imbalances, further testing for possible viruses, as well as testing for other classes of chemicals.
In the meantime, Handel has asked that anyone spotting a deformed bird to please report it, so they can continue to map occurrences of when and where birds are seen. This includes all species, not just black-capped chickadees.
Reports should include the species, when it was seen, the date and location, what the deformity looked like and which mandible was affected, and if the bird had a band. If banded, please record the color of the band and which leg it was on.
Reports can be called in locally to Liz Jozwiak at the Kenai National Wildlife Refuge at 262-7021, or to Handel directly at (907) 786-3418.
More information on black-capped chickadee deformities can be found on the Web at www.absc.usgs.gov/research/bpif/chickadees.html.
© 2018. All Rights Reserved. | Contact Us