Ecology and Management of Avian Botulism on the Canadian Prairies

64Recovery rate comparisons - 1999Data from 1999 were consistent with our initial prediction, in that recovery rate estimates forcontrol sites exceeded point estimates for outbreak sites in five <strong>of</strong> six separate comparisons(Figure 2). However, similar to 1998, the initial logistic regression model suggested aninteraction effect between treatment <strong>and</strong> region (χ 2 = 4.57, df = 2, P = 0.102). Inspection <strong>of</strong> theactual recovery rates indicated that the interaction was largely attributable to an anomalouspattern in the data from AB. Specifically, whereas recovery rate estimates for outbreak sites inSK <strong>and</strong> MB were consistently lower than corresponding estimates obtained from control sites,results from AB were mixed (Figure 2). Accordingly, when recovery data from AB wereanalyzed separately from data obtained from the other two provinces, a significant effect <strong>of</strong>botulism was found for SK <strong>and</strong> MB, but not for AB (Table 3, Figure 2). Recovery rates <strong>of</strong> birdsb<strong>and</strong>ed at outbreak sites in SK <strong>and</strong> MB were, respectively, 44 <strong>and</strong> 18% lower (sexes pooled)than expected based on comparisons with control data (Figure 2).Recovery rate comparisons - 2000Results from the 2000 field season were similar to those obtained in 1999: the initial logisticregression model revealed a significant treatment-by-region interaction (χ 2 = 7.48, df = 2, P =0.024) <strong>and</strong> inspection <strong>of</strong> recovery rate estimates suggested that the interactive effect was largelydue to the pattern in AB differing from that observed in the other two provinces (Figure 3).Thus, we again treated data from AB separately in the final analysis. Results indicated a highlysignificant treatment effect in SK <strong>and</strong> MB (Table 4), with recovery rates <strong>of</strong> birds b<strong>and</strong>ed atoutbreak sites being 14-35% lower (sexes pooled) than expected based on comparisons withcontrol data (Figure 3). Interestingly, the opposite pattern was evident in AB (Figure 3),although recovery rate differences between outbreak <strong>and</strong> control sites in that province were onlymarginally significant (Table 4).Clean-up versus no clean-up on botulism-prone wetl<strong>and</strong>sOver all years, field crews working at botulism outbreaks sites trapped <strong>and</strong> released 6,594 adultsmallards (annual totals for 1998, 1999, <strong>and</strong> 2000 were 1,057, 1,679, <strong>and</strong> 3,858, respectively;Table 5). Partitioning data by sex <strong>and</strong> site, direct recovery rates ranged from 0-5.7% in 1998, 0-8.0% in 1999, <strong>and</strong> 0-16.7% in 2000 (Table 5). For reasons explained above, recovery rates <strong>of</strong>males almost invariably exceeded those <strong>of</strong> females (Table 5).If carcass removal is effective at reducing botulism-related mortality, one would expect recoveryrates <strong>of</strong> birds b<strong>and</strong>ed at managed sites to be greater than those <strong>of</strong> birds b<strong>and</strong>ed at unmanagedsites. Results from 1998 were consistent with this expectation, in that recovery rates <strong>of</strong> birdsb<strong>and</strong>ed at Pakowki Lake, AB (a removal site) exceeded those <strong>of</strong> birds b<strong>and</strong>ed at Old WivesLake, SK (a non-removal site; Table 5). However, formal analysis indicated that, aftercontrolling effects <strong>of</strong> sex <strong>and</strong> date <strong>of</strong> b<strong>and</strong>ing, differences between the two sites were no greaterthan expected based on sampling error (P = 0.651; Table 6). Similar results were obtained for1999 (Tables 5 <strong>and</strong> 6).