Survival of radio-marked mallards in relation to management of avian botulism.

Avian botulism outbreaks are frequently perpetuated by type C toxin produced by Clostridium botulinum proliferating in decomposing bird carcasses and consumption of toxic maggots from these carcasses by healthy birds. Therefore, removing bird carcasses has been advocated for disease management because availability of toxic maggots should be reduced, increasing duck survival. However, this management is expensive, and its effect on waterfowl mortality under field conditions is unknown. We radio-marked 419 molting mallards on 11 lakes in western Canada during July-August 1999-2001 and monitored them for 30 days, testing whether survival was higher on lakes with carcass removal. Botulism occurred on 10 lakes. On five carcass removal lakes, greater-than-normal effort was made to conduct early, thorough surveillance and immediately remove carcasses; on six nonremoval lakes, no carcasses were removed. In 1999, estimated 30-day survival probabilities ranged from 0.149 (95% CI=0.065-0.304) on one large lake with carcass removal to 0.466 (95% CI=0.270-0.674) and 0.618 (95% CI=0.443-0.767) on two nonremoval lakes. As a result, we conducted work on smaller wetlands thereafter, reasoning that any management benefit would be easier to detect. In 2000, estimated 30-day survival probabilities were 0.313 (95% CI=0.143-0.556) and 0.794 (95% CI=0.609-0.905) on two carcass removal lakes versus 0.525 (95% CI=0.362-0.682) and 0.743 (95% CI=0.564-0.866) on two nonremoval lakes. In 2001, botulism was detected on two nonremoval lakes where survival probabilities were 0.845 (95% CI=0.630-0.946) and 0.942 (95% CI=0.778-0.987), and on one removal lake where survival probability was 1.0 (95% CI=0.99-1.0), but not detected on the other removal lake where no marked birds died from botulism (1.0, 95% CI=0.99-1.0). Survival tended to be higher on lakes with lower carcass density, but when data were organized by carcass removal versus nonremoval, mallard survival was not consistently greater on lakes where carcasses were removed.

Trends in agricultural impact and recovery of wetlands in prairie Canada.

Despite widespread recognition that they provide valuable ecosystem services and contribute significantly to global biodiversity, over half of the world's wetlands have been lost, primarily to agriculture. Wetland loss is evident in prairie Canada, but comprehensive information about causes of ongoing impact for existing wetlands is lacking. Habitat data collected for approximately 10,500 wetlands during annual waterfowl surveys (1985-2005) were analyzed using multistate models to estimate rates of wetland impact and recovery from agricultural activities in the Canadian prairies. An impact was defined as an agricultural activity that visibly altered a wetland margin (natural vegetation surrounding wetland interiors) or basin (interior depression capable of holding water), whereas recovery was deemed to have occurred if agricultural activities had ceased and effects were no longer visibly apparent. We estimated separate impact and recovery rates for wetland basins and wetland margins and considered covariates such as location, time, wetness indices, land use, and wetland permanence. Results indicate that impact rates for wetland margins have declined over time, likely due to a decreasing percentage of unaffected wetlands on the landscape. Recovery rates for margins were always lower than impact rates, suggesting progressive incidence of impacts to wetlands over time. Unlike margins, impact and recovery rates for basins fluctuated with May pond densities, which we used as a wetness index. Shallow ephemeral wetlands located in agricultural fields had the highest impact and lowest recovery rates relative to wetlands with higher water permanence or situated in areas of lower agricultural intensity. High rates and incidence of wetland impact in conjunction with low recovery rates clearly demonstrate the need for stronger wetland protection in prairie Canada.