The measured length of acoustic parameters of Tawny owl (Strix aluco) males. Data are the main source for analysis of variances - ANOVA and Welch's ANOVA and Two-sample tests - Student’s Two Sample t-test and Welch’s Two Sample t-test. The first goal of the study is to evaluate and analyze the stability of selected acoustic parameters in the Tawny owl territorial call over the years. The hypothesis is that acoustic parameters vary over the years. Study sites is situated in the Malé Karpaty Mountains (the Little Carpathians) in the Slovak Republic. This mountain range is part of the Carpathians with a lower altitude (max. 768 m o. s. l.). The study area covered three smaller parts - Devínska Kobyla hill (N 48° 11.4520', E 16° 59.7587', 3 sites), Borinský karst area (N 48°16.2238', E 17° 7.3315', 4 sites) and Plavecký karst area (N 48° 29.1741', E 17° 17.2038', 3 sites). Hoot parameters were measured manually in Audacity software (spectrogram, Hanning window type, Window size - 4096) to two decimal places – the length of the first note (D1), the length of the third note (D3) and the total duration of the call (DTOT). The length of the parameters may also be affected by the distance of the owl from the recorder. For this reason, the recordings were categorised into different classes on a scale of 1–5, where 1 means the best quality with obvious details and 5 the worst quality without further information in the structure of the notes. Only recordings from 1-3 categories were used for further analysis. In these recordings all parts (D1, D2 and D3) of the hoot are visible. It is also possible to identify the shape of D3. Altogether, 13 males were recorded during the study period. However, only recordings of males who held territories for more than two years were used for statistical analysis of the parameters.
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The owl acoustical behaviour was recorded using digital recorders - Olympus DM-670 and Audiomoth. Based on previous monitoring, the recorders were placed in 10 sites with identified owl territories. The recording locations were at least 500 m apart. The recording lasted from sunset to sunrise. Each device recorded 2-21 nights. Recorders were installed at a height of at least min. 2 meters high on thin trees. They were placed in plastic bags covered with electrical tape to protect them from heavy rains. The sites were monitored from 2017 to 2020.