Posted by: atowhee | March 15, 2021



During a four-day visit to the Klamath Basin and Tule Lake NWR, there were many dead waterfowl to be seen. Beneath some raptor perches were scattered remains of half-eaten carcasses–ducks and coots. We saw one young Bald Eagle pick up a pintail corpse that was floating on the Tule Lake surface. It is likely that many of the dead, both eaten and uneaten, had been killed by botulism.

I could find no evidence online that Bald Eagles are known to be susceptible to botulism.  Invertebrates are not and botulism’s toxicity varies widely among vertebrates.  There is a fine online introductory course on  botulism in this PDF, starts on page 271

My brief summary is this: the bacterium that produces the toxin is induced to do so by an invasive virus.  Those tiniest objects are often at the base of complex natural processes.  The toxin in turn is absorbed by animals large and small.  A duck dies and maggots may begin the decomposition absorbing the botulism toxin but they will be unaffected.   Not so the shorebird, Ruddy Duck or raven who eats the maggots, or any scavenger who eats the carcass of the dead duck.  Thus does the poison get recycled.

Botulism is encouraged by a number of environmental factors—organic matter in the water (think duck feces),  low oxygen levels in water or lake or river  bottom, warmth (late summer toxins will last all through the colder winters, killing the while), modest salinity (easy to find in arid parts of Oregon), and an alkaline pH (also common in arid Oregon) all seem to encourage the botulism bacteria.  Thus Klamath and Tule NWR’s would seem to be ideal locations for annual  botulism outbreaks. Any basin where water flows in, but not out, where fecal matter concentrates and birds get crowded in by lack of wetland space can only lead to bad ends for many of the birds.

Here is recent article by Pepper Trail on botulism here in the arid west. He is a wildlife biologist, great birder and good friend who lives in Ashland.

So the botulism-plagued water at Tule Lake NWR carried corpses. The edges were rich in eagles and ravens, both adept scavengers and apparently not as likely to die of the toxin. There were at least 200 ravens, the largest concentration I have ever seen. They were there for the food, not the scenery or the climate.

Click for recent news report on the battle to limit botulism deaths at Klamath and Tule Lake. More water could ameliorate the possible plague.

It may NOT be only botulism killing birds this winter in the west. Here is email from ace birder birder Vince Zauskey on his recent inquiries about the dead birds: “I talked to a biologist working at the Shasta Valley Wildlife Area on Fri., 3/12.  He mentioned the cholera outbreak amongst Snow Geese at Tule Lake.  I mentioned the cholera outbreak to Dick A. and here was his comment, “There were a LOT of dined-upon carcasses & white goose feathers on the east shore of the large Tule Lake Sump on “A Dike Road”.  I encountered one birder from Eugene, who was somewhat distraught because she had just seen a goose in its death throes.  I have read FWS guidance stating that eagles can catch it by eating infected birds. Not a pleasant thought.”

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