Seasonal, habitat, and sex-specific food habits of red-winged blackbirds: implications for agriculture

Abstract

Seasonal, habitat, and sex-specific food habits of red-winged blackbirds were studied by stomach analysis from March through October 1977 in eastern Ontario. The overall diet is nonspecialized, but within seasons, habitats, or sexes, specializations do occur. In early spring, males eat waste grain and seeds, with birds in agricultural habitats specializing more on the former, and in nonagricultural habitats on the latter. In the breeding season, both sexes in both habitats switch to insects, although waste grain remains an important component of the diet of birds in agricultural areas. Following breeding, birds move into agricultural areas and exploit both standing oats and corn, and then waste grains again late in the fall. Some of the insects and weed seeds in the birds' diet are potentially damaging to agriculture, so consumption by birds may have direct benefits to agriculture. A cost-benefit analysis, focussing on details of the quantities and economics of consumption by red-winged blackbirds of some of these insect and weed pests should be done before widespread control of blackbirds is attempted.