The spotted sandpiper (Actitis macularia) is characterized by intense female intrasexual competition and predominantly male parental care. Females often are polyandrous. Incubating males were implanted with testosterone (T)-filled Silastic tubes. Plasma T levels were significantly elevated by T implants while prolactin (Prl) remained unchanged. Birds implanted with T deserted clutches (30%) or exhibited reduced incubation constancy (50%) while controls incubated normally. The T implants appeared to heighten sexual receptivity and hence reduce incubation constancy. Variation in male incubation behavior may have been further influenced by the degree to which males were exposed to courting females.