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.

当人口密度很高且没有个人签名时，在普查期间高估夜盲猫头鹰数量的风险就很大。黄褐色的猫头鹰的声音被证明是个体的，但迄今为止尚无任何统计技术可用于该物种的普查。为了克服这个问题，本研究提出了两种方法的组合：（1）视觉光谱比较（VSC），一种生物声学工具，它试图根据猫头鹰的视觉特征来分离猫头鹰的声音，从而对猫头鹰的声音进行声谱分类，以及（2）映射方法（MM）的广泛使用的技术。该技术被应用于居住在意大利北部孤立的落叶树林中的黄褐色猫头鹰的密集种群。该区域有14个男性领土，其密度为6.0对/公里²。多数居所范围似乎基本重叠，这一证据与该物种高地域性的普遍观念不一致。由于该技术被认为是详尽无遗的，因此对该人群的未来监视可能是准确，便宜且非常有用的。这项技术可以很容易地扩展到其他表现出个人声音线索的难以捉摸的物种。