Half a dozen Pine Grosbeaks have been found dead or dying in the Whitehorse area in the past couple of weeks, apparently victims of a fungal disease that is sometimes spread by bird feeders.

The robin-sized birds succumbed to aspergillosis, says Bruce Bennett, Wildlife Viewing Biologist with the Yukon government. He shipped one of the small corpses to the Canadian Cooperative Wildlife Health Centre lab in Saskatoon, which returned the diagnosis.

The cause of the disease is Aspergillus fumigatus, a large name for a very small organism -- a fungus much like penicillin.

"It's a very common soil fungus," Bennett explains. It occurs in damp seeds, moldy grass, rotting plant and animal matter, and sometimes in musty seeds and husks around bird feeders.

Particularly in warm and moist conditions, Aspergillus can release huge numbers of microscopic spores in a few days. If a bird breathes in enough of the spores, they grow in its lungs and air sacs, and spread through other internal organs.

"The same fungus can cause respiratory disease in humans so be careful when cleaning moldy feed, particularly in warm damp places," says Bennett.

In birds, the spores produce a condition like pneumonia. Affected birds can still hop and feed, but their lungs are blocked to the point where they can't get enough oxygen to fly, says Bennett.

"They look healthy, but they make a panting, wheezing sound."

Birds like Pine Grosbeaks are susceptible because they root around in seeds and grass, searching for the best food, Bennett explains. In the process, they sometimes breathe in enough Aspergillus spores to cause problems. Smaller birds, like chickadees, usually take one seed at a time and fly off to eat it, reducing their exposure to the spores and limiting the likelihood of contracting the disease.

Bennett doesn't know if seed from a feeder caused the cases that have shown up in Whitehorse recently. The disease can take anywhere from a few days to several months to kill its victim, he explains, so it's hard to pinpoint the source. The Grosbeaks might well have picked up the infection from rotting grass along a roadside or musty straw in a field.

However, since feeders can contribute to the problem, he recommends taking some precautions.

Store birdseed in closed containers that keep it dry, he suggests. If the seed at the bottom of the container looks moldy or smells musty, don't put it out for the birds. And if you throw it on the compost pile, make sure the compost is covered or turned regularly so that it doesn't create another source of infection.

Another good safety measure, Bennett says, is to put only two or three days' supply of seed in the feeder at any one time, and replenish it regularly. That reduces the chances of wet seed accumulating and growing moldy.

The empty husks that collect beneath the feeder can also be a source of Aspergillus, Bennett adds. Rather than being left until spring, they should be raked up before they have a chance to decompose.

Finally, it's a good idea to clean and disinfect the feeder on a regular basis. This helps prevent both aspergillosis and salmonella, another common disease that can spread at bird feeders.

A 10-percent solution of bleach will do the job, says Bennett. Smaller feeders should be immersed in the solution, and larger feeders should be rinsed. After they have been disinfected, the feeders should be dried thoroughly and restocked with clean seed.

"Aspergillosis and salmonella are the most common diseases that can be spread at feeders," says Bennett, "and these are the two things we can easily prevent or minimize."

For more information about bird feeding, or to report a sick bird, call Bruce Bennett, Yukon Renewable Resources, at (867) 667-5331.