Ecology and Management of Avian Botulism on the Canadian Prairies

21searched the area thoroughly, collecting all carcasses encountered <strong>and</strong> recording all markedcarcasses, until they felt the area was completely covered.The trial was repeated on 28 August using the same study area. Procedures were identical tothose used 10 days previously, except different coloured leg b<strong>and</strong>s were used to mark thecarcasses. Also, an additional six carcasses were collected <strong>and</strong> b<strong>and</strong>ed from outside <strong>of</strong> the studyarea, to bring the total number <strong>of</strong> marked birds distributed within the study area to 30.RESULTSEvaluation <strong>of</strong> routine clean-upThe surface area covered by open water, light, medium, <strong>and</strong> heavy vegetation on each <strong>of</strong> theresearch lakes is shown in Figure 1. The area <strong>of</strong> the lakes <strong>and</strong> the area <strong>of</strong> vegetation arepresented in Table 2. The proportion <strong>of</strong> marked carcasses found by clean-up crews duringbotulism outbreaks on the eight research lakes ranged from 7-45% (Table 2). Only 7% <strong>of</strong>marked carcasses were found on Whitewater Lake (7,850 ha), whereas 28-45% <strong>of</strong> markedcarcasses were found on lakes that were 250-550 ha in area. Kimiwan <strong>and</strong> Pakowki lakes, whichwere also large lakes, had pickup rates <strong>of</strong> 32 <strong>and</strong> 28%, respectively. However, the proportion <strong>of</strong>these lakes that was heavily vegetated, which is where most <strong>of</strong> the carcasses were found <strong>and</strong>where most <strong>of</strong> the clean-up effort was concentrated, was much smaller than the total area <strong>of</strong> thelake (Figure 3). The average cost per ha on the four small lakes was ~C$123 (Table 1). OnWhitewater Lake, the cost per ha was ~C$11 in 1998 <strong>and</strong> the clean-up rate remained at 7% in1999, despite an increased clean-up effort <strong>and</strong> a 40% increase in costs.The fates <strong>of</strong> radio-marked carcasses on three lakes with clean-up <strong>and</strong> four lakes without clean-upare presented in Table 3. Scavengers removed 7% <strong>and</strong> 5% <strong>of</strong> marked carcasses on Paysen Lakein 2000 <strong>and</strong> 2001, respectively. Although scavengers removed one <strong>of</strong> the two radio-markedcarcasses on Chaplin Lake, scavenging rate could not be determined at that site because <strong>of</strong> lowsample size. No radio-marked carcasses were removed by scavengers on the remaining fourlakes. Overall,