Douglas Main

By Douglas Main

An ongoing outbreak of botulism, a bacterial illness that causes muscle paralysis, has killed more than 94,000 birds at Tule Lake National Wildlife Refuge in Northern California, the worst such outbreak at the lake ever recorded, according to federal scientists.

Affected birds often cannot control their muscles and often suffocate in the water, said biologist and ornithologist Teresa Wicks, with Bird Alliance of Oregon, who works in the area. “It’s a very traumatic thing to see,” Wicks said.

Though local in scale, the outbreak and catastrophic die-off are tied to global problems including declining wetlands, increasing demand for limited water resources, hydrological diversions, and a warming climate.

These kinds of outbreaks can happen around the world and the phenomenon seems to be on the rise, according to Andrew Farnsworth, a scientist at the Cornell Lab of Ornithology who studies bird migration. 

“Given warming temperatures, droughts, then intense periods of rain followed by drying… the hallmarks of climate change are all over this,” Farnsworth said.

The pestilence is caused by a toxin produced by a specific type of bacteria (Clostridium botulinum) that thrives in the area’s warm, stagnant, low water levels. Botulism can also affect people, though no human cases have been reported in this instance. Other outbreaks have been reported around the world, but generally cause far fewer deaths. A botulism outbreak in 2020 caused by similar conditions killed an estimated 60,000 birds at Tule Lake. 

The Klamath Basin, of which the refuge is a part, has been disrupted by man-made dams and irrigation canals for over a century. The developments and diversions eliminated more than 90% of the area’s wetlands.

Tule Lake is an ancient water body, whose levels swelled and ebbed, but always remained, for hundreds of thousands of years. Historically, the lake and nearby wetlands would fill with water during the winter rains. Now, the water supply comes almost entirely from irrigation canals.