Habitat selection in the Dickcissel (Spiza americana) was evaluated by a comparison of over 500 nest histories from the preferred oldfield and the less preferred prairie communities in Kansas. Females are equally successful in either habitat, and their productivity is not adversely affected by their being mated by polygynous males. Thus, these two habitats are similarly suitable for females, and females are distributed simploy according to the availability of adequate nesting environments and not in any density-dependent manner or in response to density cues. No differences exist in survival rates of nests associated with individual males or in the males' individual productivities between prairies and oldfields when monogamous and bigamous males are compared. The oldfield habitat is more suitable for males, however, because the potential for sequestering more nesting sites is greater in this more heterogeneous habitat. This permits higher levels of polygyny, which increases the productivity of individual males, even though densities of birds in oldfields are greater