Posted Friday, November 5, 2004

Eared grebes dying at Great Salt Lake from avian cholera

SALT LAKE CITY — An outbreak of avian cholera has killed about 30,000 eared grebes on the Great Salt Lake.

Eared grebes are small diving birds. Each fall, about 1.5 million eared grebes congregate on the Great Salt Lake as they migrate south. The lake is a critical fueling stop for the birds. Every year, the Great Salt Lake provides the 1.5 million grebes with enough food that they're able to double their weight on route to the southwestern states and Mexico.

Avian cholera is killing eared grebes at the GSL. Photo by USFWS

Division of Wildlife Resource biologists say these outbreaks are not uncommon and there is little risk to human health. "Several avian cholera outbreaks have occurred over the past few years," said Frank Howe, nongame avian coordinator for the DWR. "This year's outbreak is one of the biggest we've seen in six years, however."

Previous avian cholera outbreaks occurred at the Great Salt Lake in 1994, 1995, 1998 and 2002. While the bacterium that causes avian cholera is not a significant human health threat, under certain conditions it may infect other bird species.

"We're keeping a close eye on the situation," Howe said. "As long as dead grebes remain in the middle of the lake, which is where they currently are, they pose only a minor threat to other bird populations. If we get a strong north wind that drives the dead grebes near freshwater sources along the south shore, however, the risk of ducks and even bald eagles being exposed to cholera increases greatly. If that happens, we may need to mobilize a major clean-up effort, like we did in 1998."

Scientists at the U.S. Geological Survey's National Wildlife Health Center have assisted the DWR in the investigation and are working with Utah biologists to monitor the situation.

Avian cholera is one of the most common diseases among wild North American waterfowl. Once birds are infected with Pasteurella multicoda, they die quickly, sometimes within six to 12 hours after infection. Live bacteria released into the environment by dead and dying birds can subsequently infect healthy birds. As a result, avian cholera can spread quickly through a wetland and kill thousands of birds in a single outbreak.

Avian cholera outbreaks occur primarily in winter and early spring. During these times, waterfowl are usually in dense groups on wintering or staging areas and may be experiencing stress due to crowding and severe weather. These conditions may serve to initiate an outbreak and facilitate transmission of the disease.

Over the past 10 to 15 years, avian cholera has recurred almost annually in several areas: southern Saskatchewan, California's Central Valley and Klamath Basin, the Texas panhandle and rice belt, the Rainwater Basin of Nebraska, and in the Mississippi and Missouri River drainages.

For more information on avian cholera, go to www.nwhc.usgs.gov/research/avian_cholera/avian_cholera.html.