The risk of overestimating the number of nocturnal owls during a census is substantial when the territory density is high and no individual signature is available. The tawny owl voice was demonstrated to be individual, but no statistical technique evaluated to date is suitable for a census of this species. To overcome the problem, the combination of two methods is suggested in this study: (1) the Visual Spectrographic Comparison (VSC), a bioacoustics tool which tries to separate owls' voices classifying the spectrograms of their calls based on their visual characteristics, and (2) the extensively used technique of Mapping Method (MM). The technique was applied to a dense population of tawny owls living in an isolated deciduous wood of northern Italy. Fourteen territorial males were individuated in the area, resulting a density of 6.0 pairs/km2. Most of the home ranges seem to overlap substantially, an evidence not in step with the common idea of high territoriality of the species. Since the technique is believed to be exhaustive, a future monitoring of this population could be precise, cheap and very informative. This technique could be easily extended to other elusive species that show individual vocal cues.