Factors associated with waterfowl botulism in the Southern High Plains of Texas
Thompson, G. Kevin
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This study was conducted on the Southern High Plains of Texas between 1 June 1982 and 1 November 1983 to monitor Clostridium botulinum type C toxin production, botulism in waterfowl, and populations of macroinvertebrates in playa lakes. Eight and 14 birds were found sick or dead on study lakes in 1982 and 1983, respectively. Six ducks, 3 in each year, were positive for botulism type C toxin. All study lakes had at least 1 duck that was positive for botulism. Four pintails (Anas acuta) (66%) one green-winged teal (A. crecca) (17%) and one mallard (A. platyrhynchos) (17%) contained C. botulinum In this study, most ducks died of botulism during September and October. However, one duck contracted botulism as early as 8 July in 1983. Thus, botulism has been observed during a 131-day period (8 July-15 November) in the Southern High Plains. Mean values for temperature, dissolved oxygen, and pH ranged between 11.0-32.0 C, 2.6-8.1 ppm, and 5.3-8.7, respectively, in playas with botulism-positive birds. One of 145 invertebrate samples tested for botulism was positive for toxin. Major invertebrate taxa collected included Chironomidae, Corixidae, Dytiscidae, Baetidae, Hydrophilidae, Gastropoda, and Oligochaeta. Although shorelines fluctuated throughout the most critical botulism periods (August-October) for this region, this was not associated with a drastic decline in numbers of a taxon or in total invertebrate abundances. Each lake contained 13 to 15 taxa of invertebrates during the study. The index for combined taxa abundance showed no significant (P>0.05) difference between years. Chironomids were the most dominant and influential constituent of playa benthic fauna. However, on one lake mayflies were the most abundant taxon. Except for Oligochaetes and leeches, no taxa showed significant differences between years. Abundances of several taxa (Chironomidae, Ephemeroptera, Gastropoda, Hydrophilidae, and Hirudinea) and total abundances had significant differences between playas while others (Chironomidae, Dytiscidae, Hydrophilidae, and Ephemeroptera) had abundances that differed between vegetation zones.