Toxin kills thousands of ducks and shorebirds

Utah wildlife: Botulism outbreak an annual event; humans are at minimal risk
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Hunters with plans to visit marshes around the Great Salt Lake for Saturday's waterfowl season opener might feel like they showed up a day late when they see dead ducks littering the water.

Utah wildlife officials are reporting that an outbreak of type C avian botulism has killed between 10,000 and 15,000 ducks and shorebirds statewide, with the majority of the dead birds on marshes of the Great Salt Lake.

"During an aerial count in the middle of September, we estimated about 6,000 dead birds on the east shore of the lake just south of the causeway," said Tom Aldrich, waterfowl program coordinator for the Division of Wildlife Resources (DWR). "Managers at the Bear River Migratory Refuge reported about 2,500 dead birds and we have had reports from the Ouray National Wildlife Refuge [near Roosevelt] of an outbreak there."

The first indication of avian botulism surfaced in mid-August when an estimated 2,000 birds were found at Farmington Bay Waterfowl Management Area.

Avian botulism outbreaks are an annual event in the late summer and early fall in Utah when dormant bacteria become active in warm water with low oxygen levels.

The toxin first shows up in invertebrates, which the ducks and shorebirds ingest. Botulism eventually paralyzes the feet and wings of the birds. Eventually they lose control of their necks and many of them drown.

"This is a drop in the bucket compared with 1997 when we estimated more than half a million birds died," Aldrich said. "That being said, this is the largest outbreak since 1997. We normally would see several hundred to 1,500 deaths from avian botulism annually on the Great Salt Lake marshes."

Humans typically are resistant to type C botulism, according to the DWR Web site, which adds thorough cooking destroys the toxin in food.

However, Aldrich said a state biologists' dog became paralyzed after retrieving hundreds of dead birds in a cleanup effort at one of the marshes.

"The dog probably ingested a ton of toxins from fetching all those ducks," Aldrich said. "We believe [the temporary paralysis] was a result of the botulism. If it was, this is only the second time in 22 years in Utah that I have known it to happen. I don't want to scare hunters with dogs; they just need to be prudent and make sure their dogs are not running free picking up ducks killed by botulism."

While most hunters won't see the impact of this year's outbreak until Saturday, some already have seen it.

People visiting Antelope Island State Park have been seeing the dead ducks since at least mid-September.

"We have been telling people as they go through the entrance station that they will see dead ducks on the causeway," said Chris Haller, assistant manager at Antelope Island State Park. "We tell visitors we know it looks bad, but that it is a naturally occurring event and that they are just unfortunate to have to see it."

Avian botulism

* Avian botulism is a paralytic, often fatal, disease of birds that results from the ingestion of a toxin produced by the bacterium Clostridium botulinum.

* Waterfowl and shorebirds are the species most often affected by type C avian botulism. Birds with the bacteria exhibit an inability to sustain flight and paralysis of leg muscles, indicated by the bird propelling itself across the water with its wings, followed by paralysis of the inner eyelid and neck muscles, which results in inability for the bird to hold its head erect. Death by drowning often follows.

* Humans are fairly resistant to type C botulinum toxin. Thorough cooking destroys botulinum toxin in food.

Source: Utah Division of Wildlife Resources