Effects of carbaryl grasshopper control on nesting killdeer in North Dakota

Abstract

AbstractThere is currently special concern for the effects of range grasshopper control on insectivorous grassland birds, such as upland shorebirds. The direct and indirect effects on killdeer (Charadrius vociferus) of carbaryl applications for grasshopper control were investigated in North Dakota in 1992. Specimens were collected from two rangeland sites aerially sprayed with 1.44 and 1.12 kg/ha of Sevin‐4‐Oil (0.56 and 0.45 kg/ha carbaryl active ingredient, respectively) and two untreated areas. Potential exposure to carbaryl, estimated from pesticide residue concentrations of whole‐body and gizzard contents, was highest 2 d after treatment and then decreased over time. Whole‐body carbaryl residues averaged significantly higher (p < 0.05) in specimens from sprayed areas, particularly from sites where the higher carbaryl application was used. There was no difference in the mean brain AChE activity and whole‐body lipid content of killdeer from treated and untreated areas. The relative abundance of arthropods (principal prey of killdeer) was also estimated on the treatment area. As expected, grasshopper densities declined significantly posttreatment but the spray caused a temporary increase in the availability of affected grasshoppers. The two application rates caused similar reductions in grasshopper numbers. Killdeer did not exhibit a functional response of a prey switch as a result of the spray, but they did demonstrate an increased arthropod capture rate for a short period (8 d) after treatment. Although exposure was documented on the higher application rate area, this exposure was apparently not high enough to cause an impact on the parameters we measured in this study. These results support the conclusions of other studies that carbaryl, applied at the rate of 1.12 kg/ha, has little impact on birds and is equally as effective in reducing grasshopper numbers as the higher application rate.