Factors influencing discrimination between insecticide-treated and untreated foods by northern bobwhite

Tests were conducted to determine at what dietary concentrations northern bobwhite (Colinus virginianus) chicks (14 days old) could discriminate between pesticide-treated and untreated food using an organophosphate (OP) insecticide, parathion, and two carbamates, carbofuran and methiocarb. Results from subacute dietary LC50 tests (one feeder of treated food per cage) were compared to tests where birds were presented with two feeders (one treated and one untreated, 1:1) or 10 feeders (five treated and five untreated, 5:5; or nine treated and one untreated, 9:1). The dietary concentration above which birds discriminate between feeders by consuming a greater proportion of untreated food is defined as the discrimination threshold (DT). The DT occurred at sublethal concentrations in all 1:1 tests, with little mortality or reduction in food consumption. Little or no discrimination was observed in 9:1 tests, with mortality similar to the LC50 tests. The discrimination response in 5:5 tests was similar to the 1:1 tests for parathion and methiocarb, but with carbofuran the DT was higher than in the 1:1 test and higher mortality was observed. In all tests, mortality was inversely related to total food consumption. No relationship was found between mortality and the amount of active ingredient ingested/bird-day. Consequently, mortality was more a function of ability to locate untreated feeders than amount of chemical ingested. When alternative food choices exist, vulnerability to poisoning can be influenced by the number and relative abundance of those choices, as well as the bird's ability to detect the chemical.