The stability of measurement parameters over the years is essential in long-term monitoring of populations. The goal of this study was to evaluate the variation of selected acoustic parameters in male Tawny Owl territorial calls. A total of ten sites were monitored in low mountains mostly covered by deciduous forests. The owl calls were recorded from February to July and in one case in September. Three acoustic parameters were analysed: the duration of the first and third notes and the total duration of the call. The third note showed the lowest coefficient of variation (10.4%) over the years. This parameter also showed the lowest range between minimum and maximum values. All parameters had higher inter-individual than intra-individual variation. The stability of the parameters was analysed in two males between two years. All parameters showed significant differences in one male. The total duration of the call was also different for the second male. Individual recognition based on the duration of notes is therefore not a suitable method for long-term monitoring. These findings may help in selecting appropriate parameters for individual recognition and a more detailed view of the stability of acoustic parameters.