(Uploaded by Plazi for the Bat Literature Project) We studied the echolocation behaviour of Nycticeius cubanus in the field in western Cuba. During hunting, N. cubanus search for insects emitting cries that sweep from 80 to 40 kHz in 4 to 12 ms. Search call characteristics correlate with the clutter structure of the hunting areas. Bats hunting in an uncluttered space broadcast longer and narrower signals, while bats hunting in cluttered space broadcast shorter and broadband signals. Longer calls were emitted with longer intervals while the duty cycle was kept below 15 % during search and approach phases. The call's minimal frequency remained about 43 kHz showing variation coefficients of less than 3%. As a consequence, bandwidth correlates positively with the maximal frequency. Calls emitted by different sympatric individuals are accurately classified by sender using a discriminant function analysis, suggesting vocal signatures in N. cubanus. The statistical analysis of several passes of calls broadcast during the hunting activity of a single individual, demonstrates a high intra-individual plasticity in vocal signatures and points to a dynamic system.