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Environmental Characteristics Associated with the Occurrence of Avian Botulism in Wetlands of a Northern California Refuge

by
Tonie E. Rocke1, Ned H. Euliss, Jr.2, and Michael D. Samuel3

Abstract: Avian botulism is an important disease affecting many species of waterbirds in North America, but the environmental conditions that initiate outbreaks are poorly understood. To determine wetland attributes associated with outbreaks of avian botulism in waterbirds at the Sacramento National Wildlife Refuge (SNWR), California, we compared environmental characteristics between wetlands where outbreaks occurred (outbreak wetlands) and did not occur (nonoutbreak wetlands). In June through October, 1987–89, we monitored the occurrence of avian botulism via observations for sick or dead sentinel mallards (Anas platyrhynchos) placed in 4 wetland enclosures. During this same time period, we collected environmental data from the water column and sediments of each wetland enclosure at 10–14-day sampling intervals. Multivariate analysis was used to reduce 22 environmental variables to 7 factors for inclusion in subsequent statistical analyses. We found that outbreak wetlands had significantly lower redox potential than nonoutbreak wetlands. The probability of botulism in sentinel mallards was associated with increasing temperature, increasing invertebrate abundance or biomass, and decreasing turbidity. However, because these factors were not consistently higher in outbreak wetlands compared to nonoutbreak wetlands, they may have a more proximate effect in initiating an outbreak.

Key words: Anas platyrhynchos, avian botulism, botulinum toxin, Clostridium botulinum Type C, environmental characteristics, sentinel mallards, waterfowl, wetlands.


This resource is based on the following source (Northern Prairie Publication 1056):
Rocke, T.E., N.H. Euliss, Jr. and M.D. Samuel.  1999.  Environmental 
     characteristics associated with the occurrence of avian botulism in 
     wetlands of a northern California refuge.  J. Wildl. Manage. 63(1):
     358-368.
This resource should be cited as:
Rocke, T.E., N.H. Euliss, Jr. and M.D. Samuel.  1999.  Environmental 
     characteristics associated with the occurrence of avian botulism in 
     wetlands of a northern California refuge.  J. Wildl. Manage. 63(1):
     358-368.  Jamestown, ND: Northern Prairie Wildlife Research Center 
     Online.  http://www.npwrc.usgs.gov/resource/birds/botulsm/index.htm 
     (Version 22JUL99).

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1U.S. Geological Survey, Biological Resources Division, National Wildlife Health Center, 6006 Schroeder Road, Madison, WI 53711, USA
E-mail: tonie_rocke@usgs.gov
2U.S. Geological Survey, Biological Resources Division, Northern Prairie Science Center, 8711 37th Street Southeast, Jamestown, ND 58401, USA
3U.S. Geological Survey, Biological Resources Division, National Wildlife Health Center, 6006 Schroeder Road, Madison, WI 53711, USA
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