Avian botulism is a toxicosis responsible for large outbreaks in wild water
fowl and wading birds. The toxin is produced by the bacterium Clostridium b
otulinum type C. We gathered existing climatological and streamflow data fo
r the Bear River Delta of northeastern Utah to determine effects of environ
mental factors on probability of occurrence of an avian botulism outbreak.
We built a logistic regression model using weather variables and streamflow
amounts for 28 years, with a response variable if an outbreak occurred dur
ing each year. Winter-summer precipitation amounts and summer streamflow we
re predictors of outbreak probability (P<0.001). Outbreaks were more likely
to occur during years of high winter-summer precipitation and high Bear Ri
ver flows during summer. We concluded that these outbreak predictors may co
ntribute to water-level fluctuations in managed wetland units, associated p
reviously with outbreaks in this and other systems.