Agelaius r. ruficapillus is gregarious, being found in large flocks in Rio Grande do Sul during most of the year; they nest in natural marshes or rice fields. This bird is accused by farmers of causing damage to rice at all stages of its growth and Belton, 1985, believes it may now be the most abundant bird in the state. Its reproductive biology in rice fields in southern Rio Grande do Sul was observed from 1981 to 1983, with more emphasis from november 1982 to march 1983. Capture and banding of 16 birds with aluminum and plastic colored bands were made; nine nests were marked with steel stakes. It was found that the male is responsible for the construction of the nest, which the female lines inside. The clutch varies from three to four eggs, three being more frequent. The female broods the eggs and leaves the nest to feed. The male stays near the nest, defending the territory. The young hatch after 13 days of brooding, and are fed arthropods by the parents. After fledging they receive grains of dehulled rice. Reproduction is synchronized with rice growth. It begins with flowering and ends at harvest time. Adult birds feed on rice during the entire growth period, taking the "milk" of green rice and eating ripe grains after dehulling them.