While avian cholera is lethal to waterfowl and other water birds, it does not affect humans. Avian cholera (not related to human cholera) is a common disease of North American waterfowl and results from infection with the bacterium Pasturella multocida. It spreads rapidly from bird-to-bird and can kill thousands of birds in a single incident. A bird infected with avian cholera dies quickly. Avian cholera die-offs in waterfowl commonly occur during the winter months in California, especially during cold spells and fog.

"California and many other states experience waterfowl die-offs from avian cholera annually," said Dan Yparraguirre, Department of Fish and Game (DFG) wildlife biologist. "California is the winter home and migration area for over 60 percent of the waterfowl that winter in the Pacific Flyway. The Midwinter Waterfowl Survey indicates that between four and six million waterfowl occur in California, making this state, particularly the Central Valley, one of the most important wintering areas for waterfowl in North America."

Cold weather and high concentrations of waterbirds create ripe conditions for incidents of avian cholera. California currently has three recent occurrences at Butte Sink Wildlife Management Area (Colusa County), Merced National Wildife Refuge (Merced County), and a suspected incident at Clear Lake (Lake County). More occurrences are possible as the winter continues, especially in the Central Valley which is a primary destination for overwintering waterfowl, although normally losses diminish in late February as migration southward begins.

Dense concentrations of birds enhance the transmission of the bacteria which spreads rapidly through bird to bird contact, contact with secretions, or ingestion of contaminated food or water. Though avian cholera does not affect humans, people should avoid contact with any sick bird or animal. Diagnostic tests conducted on birds involved in the die-offs at Butte Sink and Merced confirmed avian cholera, and preliminary results indicate the presence of Pasturella at Clear Lake.

Signs of sickness from avian cholera in birds include:?Į?Ģ A sudden die-off of many birds?Į?Ģ Lethargy?Į?Ģ Convulsions?Į?Ģ Swimming in circles?Į?Ģ Throwing the head back between the wings?Į?Ģ Erratic flight such as flying upside down or trying to land a foot or more above the water?Į?Ģ Mucous discharge?Į?Ģ Soiling or matting of the feathers around the vent, eyes, or bill?Į?Ģ Pasty, fawn-colored or yellow droppings?Į?Ģ Blood-stained discharge

Over the last 30 years in California, documented bird losses due to diseases and pollution ranged from a low of 10,500 in 1977-78 to a high of 169,300 in 1991-92. The majority of the bird losses in 1991-92 consisted of 150,000 eared grebes that died due to avian cholera at the Salton Sea. Average annual loss of migratory birds to disease in California is about 25,000 birds. These figures are for birds picked up and disposed of, and the actual losses are greater. In 2005, the last full year of available data from the National Wildlife Health Center, of the nearly 12,000 birds picked up in California, most diagnosed causes of mortality were: petroleum spills (5,000); salmonellosis (2,400); botulism (1,800) and starvation (1,500).

The DFG and the U.S. Fish and Wildlife Service work closely and quickly in responding to any water bird die-off in California which involves the prompt removal and disposal of dead birds. Samples are collected for diagnostic testing to verify presumptions of avian cholera and to test for other diseases such as avian influenza. Dead wild birds should be reported to 877-968-2473.