Reproduction by an altricial songbird, the red-winged blackbird, in fields treated with the organophosphate insecticide fenthion

(1) Breeding red-winged blackbirds were used as a model to study the effects of a single application of an organophosphate insecticide, fenthion, on reproduction of altricial songbirds.

(2) The insecticide had no significant effect on frequency of nest abandonment, clutch size, hatching success, or fledgling success.

(3) Growth rates of young nestlings were lower in nests on one of two treated areas, but overall growth rates of survivors were not significantly different from controls in nests on nearby unsprayed areas.

(4) The insecticide had no measured effect on male spatial organization.

(5) Measures of abundance of the principal nestling food item, noctuid larvae, showed that one application of the insecticide 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.