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California Warns of Bird Botulism Outbreaks

Mallards like this handsome fellow are frequent victims of avian botulism | Photo: Nathan Ruppert/Flickr/Creative Commons License

As California's lakes and ponds grow ever smaller in this third year of drought, the state's Department of Fish and Wildlife is warning that wild birds are likely to fall victim to a fatal disease linked to stagnant water, and they're asking for your help tracking down victims.

The culprit is avian botulism, caused by the bacterium Clostridium botulinum. Clostridium thrives in water that's been depleted of dissolved oxygen. In drought years, when lakes and ponds become smaller and more shallow, average water temperatures rise. Warm water promotes the growth of bacteria that feed on decaying vegetation. Those bacteria can quickly use up most of the oxygen in the water, which allows Clostridium to flourish.

Clostridium secretes the chemical botulinum, the most potent toxin known to science. When waterfowl ingest food or water contaminated with the bacterium they can quickly succumb to nervous system damage from botulinum poisoning. Previous outbreaks of avian botulism in California have killed as many as 46,000 birds. An outbreak at the Tule Lake National Wildlife Refuge in the summer of 2013 killed thousands of ducks. This year's continuing drought makes a repeat of such outbreaks a strong possibility.

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Compounding the problem is the fact that once a water bird dies of botulism, its submerged carcass can become a breeding ground for more Clostridium. The California Department of Fish and Wildlife says that prompt cleanup of waterfowl carcasses may well help limit the spread of the disease.

CDFW wants to hear from property owners in the state who find either waterfowl carcasses or obviously ailing birds on their property. (We assume this request also extends to non-property owners who witness similar sad situations.) Birds with avian botulism may exhibit paralysis or convulsions, limp wings or necks, or inability to swim.

You can report possible outbreaks of avian botulism in the state using CDFW's online mortality report form.

And though the risk to humans from avian botulism is relatively low, it's never a great idea to handle dead or injured wildlife. (Given that many of the potential botulism victims are game birds, we probably ought to add "especially don't eat them.") Instead, notify CDFW and let the professionals handle it.

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About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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