Reproduction by an altricial songbird, the red-winged blackbird, in fields treated with the organophosphate insecticide fenthion.
The breeding of red-winged blackbirds (Agelaius phoeniceus) was used in 4 flood-irrigated hay meadows in Wyoming as a model to study the effects of a single application of fenthion (an insecticide that is commonly used against mosquito larvae) on the reproduction of altricial songbirds. The insecticide had no significant effect on frequency of nest abandonment, clutch size, hatching success or fledgling success. Growth rates of young nestlings were lower in nests in 1 of 2 treated areas, but overall growth rates of survivors were not significantly different from controls in nests on unsprayed areas nearby. The insecticide had no measured effect on male spatial organization. Measures of the abundance of the principal nestling food item (noctuid larvae, especially Polia sp.) showed that 1 application of fenthion significantly reduced the abundance of the food supply, but the reduction of food supply did not result in a decrease in nestling growth rates or fledgling success.