Avian Botulism Outbreak in Klamath Basin and Tule Lake Refuges

August 9, 2024

Another outbreak of avian botulism is killing birds throughout the upper Pacific Flyway in the Klamath Basin and Tule Lake National Wildlife Refuges.

Waterfowlers, birdwatchers, and conservationists alike rejoiced this spring when the Bureau of Reclamation (BoR) allocated water for the Lower Klamath and Tule Lake National Wildlife Refuges in Southern Oregon and Northern California. For the first time in several years, water would be put on to the wetland systems for wildlife on their spring migrations. Many were hopeful that the influx in water resources would bring new life to these critical stops for migratory waterfowl and shorebirds on the Pacific Flyway after years of drought and underallocation of water resources even after the record rains of 2022-2023.

Then, the first boot fell when the pump houses were turned off weeks earlier than anticipated this spring. Now, the second one has started to fall: avian botulism outbreaks due to the warm, stagnant waters in the refuge systems.

Water Allocation

Lower Klamath and Tule Lake National Wildlife Refuges are an important part of the overall health of the Klamath Basin; they are used by approximately 80%, or 5 million, of the Pacific Flyway’s waterfowl for all life history stages. Without periodical water additions, one could anticipate an outbreak of avian botulism. In a public call to the Commissioner of BoR in July, the Klamath Water Users Association (KWUA) asked for the Bureau and refuge managers to work together to get cool water flowing through the system. Cool waters that would postpone and mitigate any chance of avian botulism.

“We are grateful that we could provide water to Lower Klamath this year, especially in the amount the district was able to send down there,” said Scott White, manager of the Klamath Drainage District (KDD). “But this is something all of the stakeholders need to participate in. Everyone in the basin needs to dig deep into their pockets and see how they can help keep water flowing to the refuges because we’re struggling to find more on our end.”

Also in July, the California Waterfowl Association (CWA) made a public call citing the dangers of an avian botulism outbreak should additional water deliveries to Tule Lake and Lower Klamath refuge systems not be made. Mark Hennelly, Vice President of Advocacy for CWA, states, “Together with Ducks Unlimited, we are sending a letter to the Bureau of Reclamation stressing the immediate need for additional summer water deliveries to the Klamath refuges.”

What is Avian Botulism?

Avian botulism is a naturally occurring bacteria that is in the soil and, when it comes to life, produces a toxin. Waterfowl can get it by eating aquatic invertebrates which filter feed on particulates in the water. The toxin attacks the nervous system of the bird, inhibiting muscle movement, leading to clinical signs of weakness, lethargy, and inability to fly or hold the head up. This is what leads to the deaths of the birds, drowning. After a few ducks succumb to this, maggots appear. The maggots amplify the lethality of the toxin, and the outbreak explodes as other birds eat these time-bomb maggots.

The last widespread outbreak of avian botulism in the region occurred in 2020; again, a low water level and warm water temperature scenario. Tule Lake National Wildlife Refuge alone lost an estimated 60,000 ducks to avian botulism.

Brian Huber, waterfowl biologist for CWA, says that the usual timing of the botulism hits hard when birds are molting. “Birds that are molting need protein. This is when they are eating a heavy diet of aquatic invertebrates that are holding the toxins.” When the birds die and are not picked up by biologists during surveys or banding programs while they are in the marsh, biomagnification occurs when other birds eat the maggots off of the expired birds that hold the toxins.

The value of quality summer habitat for late-season nesting and molting birds far outweighs having a botulism outbreak. When water is available, this can help manage the severity of an outbreak.

How Do We Stop This From Happening?

Avian botulism does not account for a high percentage of total waterfowl loss each year compared to other factors, such as birds downed and unrecovered by hunters. However, it is a shocking yet, to a degree, preventable consequence of resource management.

More moving water on the landscape, resulting in cooler surface water temperatures, lessens the risk of an outbreak. While annual outbreaks of botulism cannot be eliminated, the extent of these events can be limited by managing water levels and by collecting sick or dead birds from the wetlands so they don’t infect others. Presently, the KDD is working with the USFWS to pump additional water into a unit on the Lower Klamath refuge to curtail an outbreak and establish a rehabilitation area there.

Like in 2020, local wildlife caregivers Bird Ally X will assist in rehabilitating waterfowl. Ducks Unlimited is also helping with resources for the “Duck Hospital” being operated by Bird Ally X. Flushing out their system with a fresh diet and water before releasing them has helped reduce the numbers lost. Typically, rehabilitated birds are banded to track how well they do after recovery. Unfortunately, the presence and risk of spreading avian influenza is preventing the hospital from getting underway. Once avian influenza is not a human health risk, the hospital is ready to mobilize.