Non-target hazard to ring-necked pheasants from zinc phosphide use in northern California agricultural areas
The National Wildlife Research Center (NWRC) conducted a field study to determine hazards to non-target gallinaceous birds following the use of 2.0% zinc phosphide (Zn3P2) baits for vole control in fall alfalfa. Consultation among the NWRC, USDA Wildlife Services, California Department of Food and Agriculture (CDFA), U. S. Environmental Protection Agency (EPA), and the California Department of Fish and Game produced a 3-phased study. Free-ranging ring-necked pheasants and California quail were studied in alfalfa during the concurrent harvest of other agricultural crops. These data would be used by CDFA to support the re-registration of their label “Rodent Bait Zinc Phosphide Treated Grain (2.00%)”, EPA Reg. No. CA890027. Phase 1 was a pilot study to determine whether the two test species could be maintained in walled enclosures. Phase 2 was a worst-case-scenario using the test species in alfalfa enclosures during vole control (i.e., simulated field study). Information from the 14-day post-baiting period led to a better understanding of some variables, including the sub-lethal effects that could impact the design of the final phase. During Phase 3 the actual non-target field study was conducted. Results from Phase 1 showed that these species could be maintained in outdoor enclosures using only wing clipping, 1 m-high metal walls, and no covering nets. Phase 2 proved that in outdoor alfalfa enclosures, baiting for vole control was not hazardous to quail but might be to pheasants. Phase 3 concluded that 2.0% Zn3P2 bait when applied per label directions was not hazardous to either wild or pen-reared free-ranging pheasants in fall agricultural areas. This article summarizes the 3-phased study, the resulting data, and conclusions.