Males can influence current reproductive success in one of two ways: by caring for offspring or by seeking additional mates. Models for the evolution of paternal care predict increasing parental investment by males as their ability to contribute to offspring survivorship increases and as the probability of attracting additional mates decreases. I tested the assumptions and predictions of these models for polygynous Yellow-headed Blackbirds (Xanthocephalus xanthocephalus). The results of field observations and experiments indicate that male Yellowheads are capable of assessing the fitness returns associated with parental care and sexual advertisement and will increase parental investment as their ability to enhance offspring fitness increases and the probability of acquiring additional mates decreases. Thus, paternal investment is greater in unproductive marshes, on days when the insect emergence is low, when the arrival rate of unmated females is low, and for males with poor-quality territories. Current reproductive success also depends on the ability of individuals and their mates to raise young. In theory, males should be capable of assessing the parental competence of mates and adjusting their parental investment with mate quality so as to maximize the fitness return on their investment. To test this hypothesis, fitness-investment curves for nests belonging to competent and incompetent mates were derived using empirical data and, on the basis of the slopes, preferences for nests predicted. Field observations were consistent with the predictions. Males preferentially cared for young of competent mates and fed them at greater rates than young of incompetent mates; care at the latter nests occurred only when preferred nests were unavailable. Yellowheads often breed in colonies. In theory, colonies can act as information centers and facilitate the exploitation of spatially unpredictable food resources. I tested this hypothesis for Yellowheads by analyzing the pattern of (1) colony departures and (2) recruitment to an experimental foraging area. The results of the experiment and departure analysis indicate that Yellowhead colonies do act as information centers; birds can locate productive foraging areas more efficiently than in the absence of information by monitoring the success of neighbors and following them on foraging trips.