Perhaps of interest:
Contacts: Dr. Ben Gonzales, Veterinarian, (916) 358-1464
Pat Lauridson, Wildlife Biologist, (916) 445-3701
Special Feature News Release
Deadly Bird Disease Can Spread By Birdfeeders
Many Californians connect with nature by providing birds with an
outdoor birdfeeder or birdbath. But what they may not realize is those
same feeders nd baths could be harboring a deadly parasite that is
responsible for illing thousands of mourning doves, band-tailed
pigeons, and other wild birds.
Various statewide outbreaks of trichomoniasis have already caused
mortality in many of California's mourning dove and band-tailed pigeon
California Department of Fish and Game (DFG) avian experts are urging
residents to either thoroughly clean their birdfeeders and baths daily,
or remove them for the remainder of the summer to help stop the spread
of the disease.
"It's probably best to eliminate feeders all together, but if folks
decide to keep them, there are precautions they can take to minimize
the spread of the parasite to healthy birds," said Dr. Ben Gonzales, a
DFG wildlife veterinarian.
Trichomoniasis is a protozoan * a single-celled animal * that causes
mortality in doves and other gregarious species, with varying levels of
ocalized outbreaks documented annually throughout California as well as
in the arts of the U.S.
To help control the disease, DFG biologists are urging residents to:
* Replace all food in birdfeeders and water in birdbaths daily. Clean
up old food around feeders daily, and only use small amounts of food.
* Decontaminate feeders by using a 10 percent solution of household
bleach in water, preferably cleaned just prior to adding new food.
* Spread small amounts of seed out over a large area in the sun,
instead of using bird boxes or feeders. Also vary the location of where
the seed is spread to avoid encouraging a concentration of birds at one
DFG's biologists say the disease is highly contagious and can easily
spread from birds sharing the same feeding or watering areas. Young
doves and pigeons can become infected when fed "crop milk" is produced
by their parents.
"The major concern with the spread of this disease is the impact it
has on local wild bird populations," Gonzales said. Although exact
numbers of bird deaths is impossible to calculate, Gonzales believes
the number to be in the thousands so far this year.
Understanding the spread of disease, including other agents transmitted
at feeding and watering sites, and their impacts on bird populations,
is a major consideration for wildlife professionals who are charged
with the management of wild birds in California.
"Unusual population increases that result from feeding as well as a
concentration of birds around feeders, predispose bird populations to
outbreaks f infectious diseases like Trichomoniasis," Gonzales said.
"This problem occurs rimarily in urban areas in mourning doves."
Environmental conditions are also a factor with the disease. The
parasite enerally poses little threat until temperatures exceed 75
degrees ahrenheit and evening lows are above 50. Outbreaks are
typically documented during the drier seasons
* spring, summer and fall, during the months that many bird watchers
rely on bird feeders and baths.
Birds that are concentrated, feeding at one location, are most
vulnerable to this disease because the parasite is typically passed in
food and water regurgitated from an infected bird. Healthy birds that
ingest such food, or drink the same water as an infected bird, can then
contract the disease.
Nationwide studies suggest that a significant number of doves and
pigeons are currently infected with varying strains of the disease.
Thousands of these birds die each year. Mortality in young birds is of
particular concern. Gonzales said nestlings typically die within four
to 18 days after being infected.
"This disease can impact the number of young birds being recruited into
a population, which then can impact future local populations," said Pat
Lauridson, DFG wildlife biologist and game bird specialist. "If a
parent is infected and the only means of survival of the young is by
that parent, as is especially the case with doves and pigeons, the
young are given a death sentence."
Studies show that the parasite can last for 20 minutes to several hours
in water, and up to five days in bird feed. "This is ample time for the
disease to be transmitted to a healthy parent bird that happens to feed
from the same infected feeder or watering bowl," said Gonzales, who
conducts necropsies on infected dead birds and compiles estimated
mortality rates for DFG.
Doves and pigeons are the two species most documented with the
infection because of their gregarious habits, and their feeding of
young with crop milk, noted Gonzales. The infection essentially affects
their upper digestive tracts. The birds develop lesions in their mouths
and throats that eventually prevent them from eating. Most of these
birds die of starvation but some actually suffocate from the lesions or
when the disease impacts their livers.
"Infected birds will continue to attempt to eat seeds or drink water,
even though their throats are often blocked by the parasite, because
they are starving or dying of thirst, in addition to the infection," he
said. "It can spread like wildfire and to a variety of other bird
species." Falcons and hawks can become infected after feeding on dead
doves, for example. Owls and songbirds can also contract the disease
Most often, however, dead doves and pigeons are found because they tend
to die in the open, whereas other bird species seek cover just prior to
their death. In addition, because of their flocking behavior, doves and
pigeons often die in groups, thereby increasing the chance of a die-off
"The potential impact to local band-tailed pigeon populations in high
outbreak years is worrisome," said Lauridson, who is charged with
developing management objectives for both doves and pigeons in
The band-tailed pigeon, distinguishable by its yellow legs, yellow
bill, and long banded tail, is the only native and the largest pigeon
in North America. And California is home to a geographically unique
population of this bird. The Pacific Coast band-tailed pigeon migrates
from British Columbia to northern Baja, California. It is also a bird
that generally prefers a distinct habitat, the state's conifer, pine
and mixed hardwood forests found at higher elevations.
"The band-tailed pigeon is kind of a majestic bird. Its migratory
behavior and proclivity for forested habitats makes it much different
than the feral pigeons you see roosting in the rafters of a barn,"
Lauridson said. "But all the same, if these birds find an easy food
source such as what feeders provide, they'll return in even larger
numbers to feed alongside other species, which creates an environment
rich for the transmission of the disease and resulting impacts to local
European settlers who brought pigeons and doves to the continent
introduced the Trichomoniasis parasite in the U.S. The avian disease
likely went undetected for centuries. It was first documented in the
Southeastern region of the U.S. between 1949 and 1951. Nationwide
mortality rates at that time were only in the tens of thousands for
mourning doves. Several decades later, the disease spread to other
areas, including the states of New Mexico, Alabama, and Nebraska. In
1988, in California the disease killed more than 16,000 banded-tailed
pigeons. This was the first major U.S outbreak recorded for the
DFG officials remind the public there is always a danger in handling
dead wildlife. Individuals should wear gloves when picking up a dead
bird or other wildlife and always wash with an anti-bacterial soap
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