The recent avian cholera outbreak at Clear Lake is nothing new. Avian cholera kills hundreds of thousands of ducks annually throughout the nation.
In fact, it”s one of the most common diseases to strike wild waterfowl.
The last outbreak at Clear Lake was in 2004 when more than 8,000 ducks died. In the Sacramento Valley, cholera outbreaks have killed thousands of ducks and geese in past years.
Avian cholera is caused by a bacterium called “Pasteurella multocida” Type 1. The bacteria can be transmitted by bird-to-bird contact from secretions or feces of infected birds. The disease also can be spread by ingesting food or water containing the bacteria. Aerosol transmission may also occur. The bacteria can survive up to four months in soil and water.
Avian cholera is highly contagious and can spread rapidly. The most used preventative method is to collect the dead carcasses. In some cases, the Department of Fish and Game (DFG) will use air boats to disperse the healthy birds. That won”t happen at Clear Lake and the primary method will be to collect and bury the dead birds.
As was the case back in 2004, the disease will be gone when the ruddy ducks leave the lake and continue their northward journey. Most of the ruddy ducks will be gone by late February.
The ruddy duck has been the primary carrier of avian cholera at Clear Lake and 90 percent of the infected birds are ruddy ducks, the reason being that they tend to form tight flocks and raft in the middle of the lake. When birds are that close together, it only takes one or two ducks that have the disease to infect hundreds of others. It would be like if 100 people were crammed in a small room and a couple of others walked in carrying the flu and began to sneeze. In the end, a good portion would become infected.
Ruddy ducks are classified as diver ducks. Hunters rarely kill a ruddy duck because they are considered poor eating. They tend to stay out in the middle of the lake in small flocks of up to 50 birds. Their primary diet is vegetable matter, but like all diver ducks, eat small fish, small crustaceans and midge larva.
Ruddy ducks belong to a class of ducks called stifftails. There are only six species of this type in the world and three live in North America. They are a small gray-brown duck weighing from 1-2 pounds and can be identified by the white check patch. When disturbed they would rather dive then fly. When they do fly it”s usually low over the water and at high speed. They are unusual in that they only migrate at night.
Approximately 40 percent of the ducks infected with fowl cholera die. The birds normally succumb within 10-12 hours after contacting the disease. At times, death comes so quickly from cholera that birds have been known to fall out of the sky. In fact, it”s rare to see sick birds because death comes so quickly. The other birds that don”t die become carriers of cholera and can infect any bird they come into contact with. The disease isn”t spread to humans.
Ruddy ducks only use Clear Lake during the winter months and the population can vary from a couple of thousand birds to more than 15,000. The main buildup starts during the months of January and February when the ducks are headed north. They use Clear Lake as a resting area.
The big fear among wildlife biologists is that the cholera will spread to other species of water birds that are now at Clear Lake. There are presently 50,000 western grebes, not to mention seagulls, pelicans, cormorants, osprey, coots and other ducks and geese on the lake. Most of these birds are located in the Clearlake Oaks Arm and the Redbud Arm. Ruddy ducks have been sighted among the grebes and gulls. If the disease spreads to these birds, the results could be devastating.
The DFG doesn”t want local residents to handle the dead ducks. If you find dead birds, call 275-8862 and report the location and a DFG team will pick up the carcasses.
