Cues and social information are important in the decisions many animals make to settle. In colonial seabirds, such decisions are based upon information gathered during a prospecting phase, in which for young individuals social information from conspecifics is key. Yet the specific cues that prospectors use, and why, remain debated questions. We used an experimental approach to evaluate a conspecific-attraction hypothesis, predicting that during nocturnal prospecting Ancient Murrelets (Synthliboramphus antiquus) use social information in the form of audio cues. Specifically, we used playback experiments to test whether prospectors use conspecific vocalizations to locate potential breeding sites, and we hypothesized that prospectors' activity should increase during playback of conspecific calls. Using an information-theoretic approach we found that, as predicted, playback increased Ancient Murrelet activity, supporting a conspecific-attraction hypothesis. During playback, activity increased over background levels by 271% at Langara Island and by 458% in the Aleutian Islands. In addition, Ancient Murrelet activity decreased with increasing wave height, as moon phase approached full, and with increasing distance to the nearest occupied colony. We conclude that prospectors use conspecific vocalizations to locate potential colony sites and that playback may be used in management to speed the process of recolonization of areas from which the species has been extirpated historically.