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The first post on this topic established that the Salton Sea is an ecological oasis and one of the last existing stops in southern California for migratory birds along the Pacific Flyway. However, it was mentioned previously that there are many factors which are threatening this avian Eden. Each of these threats will be addressed in more detail individually, with the first being avian botulism toxin.

Avian botulism toxin is produced by the bacteria Clostridium botulinum. While the bacteria is commonly found in soils and wetlands, it will not produce the botulism toxin unless certain environmental conditions are met. In order for the bacteria to produce the toxin, it needs an anaerobic environment, warm temperatures, and a protein source.[1] Do these conditions sound familiar? In the summer, low dissolved oxygen levels, high temperatures, and the presence of dead algae (protein source) in the Salton Sea provide an ideal environment for the growth of C. botulinum and the subsequent production of avian botulism toxin. Similarly, the bacteria can enter tilapia, and when the tilapia die or are eaten by the birds, the toxin can be transferred through the dead carcass/maggot pathway.[2] Once the toxin is produced, flies lay eggs in the carcass, the bacteria and toxin enter the maggots, and then the maggots or the whole carcass are eaten by the birds. The bird then reacts to the neurotoxin and dies, thus continuing the cycle.

The production of avian botulism toxin can lead to an outbreak of avian disease, referred to as an epizootic, which is an analogous to a human epidemic. This is supported by the fact that epizootics caused by avian botulism toxin at the Salton Sea have been reported since at least 1975.[3] However, the largest outbreak occurred in 1996, where over 20,000 birds became sick and 15,000 birds died of avian botulism toxin.[4][5] These numbers include more than 1,200 California brown pelicans, which were on the endangered species list at the time (they were removed from the list in 2009. While the biggest epizootic occurred in 1996, smaller outbreaks have occurred almost annually since then.

A white pelican being treated for avian botulism toxin.
A white pelican being treated for avian botulism toxin.

Due to the fact that avian botulism toxin is a huge threat to the birds of the Salton Sea, the U.S. Fish and Wildlife Service has been working to prevent epizootics like the one in 1996. Since the disease is mainly spread through the maggot cycle, carcasses should be removed as soon as possible to avoid the hatching of the maggots. However, millions of tilapia die at the sea every year, so all the carcasses cannot be collected. If sick birds are observed, they are collected and given aid to prevent mortality.[6][7] However, these actions are expensive and are only addressing the symptoms of the problem. For instance, in order to stop the 1996 epizootic, the US Fish and Wildlife Service spent over half a million dollars.[8] The real problem lies with the state of the Salton Sea and the lack of public interest and political will to take action before it is too late for this avian paradise. Can we come together to implement a solution for the Salton Sea or will this be another case of paradise lost?

Written by Jaben Richards

[1] http://www.nwhc.usgs.gov/disease_information/avian_botulism/

[2] http://www.fws.gov/saltonsea/botulism.html

[3] Dennis Jerome Hosier, “The ecology of avian botulism at the Salton Sea,” Master of Science Thesis, (1975) California State Polytechnic University, Pomona, CA

[4] P. Nol, T.E. Rocke, K. Gross, and T.M. Yuill, “Prevalence of neurotoxic Clostridium botulinum type C in the gastrointestinal tracts of tilapia (Oreochromis mossambicus) in the Salton Sea,” Journal of Wildlife Diseases, 40(3), (2004), pp. 414–419

[5] Tonie E. Rocke, Pauline Nol, Charles Pelizza, and Ken K. Sturm, “Type C botulism in pelicans and other fish eating birds at the Salton Sea,” Studies in Avian Biology No 27 (2004), pp. 136-140.

[6]  http://www.fws.gov/saltonsea/botulism.html

[7] Photo by Milton Friend. Available at: http://www.sci.sdsu.edu/salton/BioscienceSavingSaltonSea.html

[8] Rocke et al. (2004)