ABSTRACT
: This field study used a precise method of assessing effects of insecticides on bird populations by establishing a marked population before application and determining survival rates of known individuals after application of the insecticides. We investigated the effects of two organophosphate granular insecticides applied to cornfields in southwestern Ontario to combat the corn rootworm (Diabrotica spp.). Nine control fields and 11 treated fields, six of which were treated with Fonofos (Dyfonate 20G) and five treated with Terbufos (Counter 15G), were chosen. A colour-banded population of 228 Song Sparrows (Melospiza melodia) was established and numbers monitored before and after application of the insecticides. Activity watches showed that territorial individuals spent at least some of their time foraging on the cornfields. There was no evidence that the insecticides affected the survivorship of either male or female Song Sparrows in the test population. Results from analyses of counts suggest no dramatic impact in three other species of passerines (Horned Lark Eremophila alpestris, Savannah Sparrow Passerculus sandwichensis and Vesper Sparrow Pooecetes gramineus). Sublethal effects of the insecticides on reproductive success of the Song Sparrow population were investigated. Ninety-one nests were found and their outcome (successful or failed) determined. Nest watches showed that parents collected some food for their young from cornfields in at least half of the nests. None of the reproductive parameters measured - reproductive success, clutch size, number of unhatched eggs, number of young fledged per nest - differed among the two types of treated fields and the control fields. In conclusion, the Song Sparrows studied were not ingesting the insecticide granules in lethal doses or in amounts sufficient to affect reproductive success and, hence, no differences in survivorship of adults nor in those reproductive parameters measured among the three field types were detected.
