Sunflower Depredation and Avicide Use: A Case Study Focused on DRC-1339 and Risks to Non-target Birds in North Dakota and South Dakota

摘要

Agricultural land-use, cropping practice, agrichemical use, and wildlife interactions have long provided conflicts between wildlife needs and human uses of habitat. For example, sunflower seeds ripening in late summer and early autumn throughout agricultural areas of North Dakota and South Dakota are highly sought food items for red-winged blackbirds, common grackles, and yellow-headed blackbirds. Unfortunately, loss of sunflower seeds prior to fall harvest has been attributed to these birds, with crop losses estimated at greater than $5 million per year. An avicide, DRC-1339 (3-chloro-p-toluidine hydrochloride), has been proposed for use in spring baiting programs in North Dakota and South Dakota to control fall depredation of the sunflower crop. An estimated 60 species of non-target birds with varying sensitivities to DRC-1339 occur near spring baiting sites, with nearly half of these species being granivores that might feed on the DRC-1339-treated bait. At least nine species are birds of management concern. Our work evaluated risks to non-target birds that are potentially associated with DRC-1339 spring baitings. From the current analysis, spring baiting presents risks to non-target birds, especially small-bodied species characterized by marked responsiveness to DRC-1339, e.g., ingestion of a single baited grain will likely yield mortality in a small-bodied bird. A simple comparison of hazard quotients for small-bodied nontarget birds and target birds suggests these species have similar risks for dietary exposures to DRC-1339. At present mitigation practices are unproven with respect to minimizing non-target bird loss. Potential losses from non-target population presently thought to be declining suggests that risks vary across the relatively simple "non-target" category, and risk managers must be wary of oversimplifying management plans based on a "non-target" and "target" categorization of species at-risk. In view of the uncertainties apparent in the present analysis, as well as other risk assessments focused on the issue, decisions regarding DRC-1339's use hinge on differing management perspectives of "acceptable risk" and resource valuation. Only when these issues are resolved can resource management plans benefit the long-term sustainability of resources at risk.