Providing Expert Support at Tulare Lake Avian Botulism Event

Emily Werdal, Wildlife Rehabilitation Technician, and Kylie Clatterbuck Wildlife Manager, tube-feed Black-necked Stilt at the Los Angeles Wildlife Center rescued from Tulare Lake avian botulism incident. Photo: Ariana Gastelum–International Bird Rescue

Since August, a serious avian botulism outbreak affecting waterbirds has been unfolding in California’s Central Valley.

Migrating birds spending time at Tulare Lake are being exposed to this deadly neurotoxin. Unfortunately, in the past four weeks, thousands of dead birds have been collected at the lake 40 miles south of Fresno, CA, and winter migration is only just getting started.

Luckily for affected birds, there’s a plan in place. The California Department of Fish and Wildlife (CDFW) has enlisted the Oiled Wildlife Care Network (OWCN) to manage the response. International Bird Rescue has been activated along with other member organizations to assist in this rescue and rehabilitation effort. Hundreds of birds, especially ducks, grebes, stilts, and ibis have come into care and many have already recovered and made it to release.

Tulare Lake botulism birds recovering: American Green-winged Teals are moved to the waterfowl pens at Bird Rescue’s Los Angeles Wildlife Center by Kylie Clatterbuck, Wildlife Center Manager. The birds receive care to flush the neurotoxin. Photo: Ariana Gastelum–International Bird Rescue

Over its 52 years, Bird Rescue has had extensive experience with botulism. Since our beginnings in 1971, Bird Rescue has responded to multiple botulism events at Lake Merritt in Oakland, the Salton Sea (American White Pelicans), Ballona Creek (ducks) in Los Angeles, as well as dozens of other similar outbreaks in urban lakes and ponds throughout California. For this response, our trained staff has joined other wildlife responders to assist in the care of affected birds, and Bird Rescue’s Los Angeles wildlife center is one of the facilities caring for affected animals.

What causes botulism?

Avian botulism is a condition brought on by the consumption of a toxin produced by the naturally-occurring bacterium Clostridium botulinum. Lakes and ponds with low inputs of fresh water, low oxygen levels, and ample decaying organic material are at risk for this problem occurring, especially when the water becomes warm and stagnant during hot weather. Urban ponds with poor water quality during the heat of summer are common sites of botulism outbreaks. The bacteria can produce spores that can remain dormant on the bottom for many years. Once the conditions are right for bacterial growth again, the toxin-producing bacteria can begin multiplying, and birds can become affected during their normal foraging for food.

Usually, the first sign of this problem in birds is partial paralysis. Ultimately, affected birds become unable to even hold their heads up, and death occurs most often from drowning. In a large outbreak, many thousands of birds may die, and as dead birds accumulate, the bacteria multiplies even more and causes more and more deaths. For this reason, one way that people control outbreaks is by promptly removing the carcasses of deceased animals. As bad as all that sounds, with prompt rescue, birds that are affected by the toxin but have not yet succumbed to drowning typically have an excellent prognosis for rapid recovery. With supportive care matched to the severity of each bird’s symptoms, birds with botulism usually recover very quickly and usually are ready for release within two weeks.

Most years, Tulare Lake is a dormant body of water. With heavy winter rains, the lake grew to the size of Lake Tahoe. In its wake, it swallowed up working farms in the southern end of the Central Valley. Because this is migration season, the response has increased urgency. The lake now has the ability to host millions of migrating waterfowl during their southern journey.

This botulism event comes on the heels of deadly and costly bird flu response, creating a high volume of patients. We are able to deploy to emergency events like this because public support helps us continue training staff and volunteers year-round.

News reports:

A big problem appears at California’s revived Tulare Lake, San Francisco Chronicle

A rescuer from California Department of Fish and Wildlife (CDFW) captures a waterbird at Tulare Lake. (CDFW photo)


Northern Pintail and Northern Shoveler recovered from botulism get released at Dominguez Gap Wetlands at the Los Angeles River. Photo by Ariana Gastelum–International Bird Rescue