Acoustic monitoring of owls in Alps

Description

The study was carried out in the Alps region. The study sites were located at an altitude of 630 – 1260 m a. s. l. Managed forests were selected from areas managed by the Bundesforste organization (N 47,792390°, E 15,003097° and N 47,788820°, E 14,873991° and one in N 47,271191°, E 12,790635°). Protected areas were localized in the Wildnisgebiet Durrenstein (WGD, N 47,762007°, E 15,021724°), Nature Reserve Kesselfall (N 47,213183°, E 12,722890°) and NP Gesause (N 47,586255°, E 14,640948°). This study compares the number of owl territories in managed and protected areas in the first goal. The second goal is aimed at the impact of the environment on owl assemblages. The data represent a table containing the results for the lines with the number of owl territories and information about environmental parameters in the 300 m buffer around the line.

Steps to reproduce

Owl calls were recorded using of Audiomoth recorders – programmable devices for ecological research. The recordings started at sunset and lasted until sunrise. The recorders were installed on sites in the WGD and managed forests around the WGD in 2021 (May, June and October) and in the NP Gesause, National Reserve Kesselfall and Kaprun (managed forests) in 2022 (April and May). We prepare pairs of lines which were placed in managed and protected forests. These pairs had similar elevation and position (on the valley bottom, on the slope – horizontal or vertical, and on the ridge). Different owl species prefer different parts of mountains. Our paired approach minimized the risk of confusing data. Recorders were placed on the 1 km line and spaced 330 meters. The number of territories was identified for each line (or group). During the field research, three recorders were broken and did not record sound. They were able to record over 20 nights. The recording was reduced in frequency – from 0 to 8 kHz – to reduce the size. Territorial calls for each species were processed individually. Tawny owl calls were compared by spectrograms. Especially the frequency and the shape of the third note were parameters useful for male identification (Fig 1). The number of territories by other species (the Pygmy and Boreal owl) was identified by different sound frequencies and when more males were recorded together. Recordings from the same time period were analyzed together for all recorders on the line. The number of territories was based on the number of individual territorial males. Contact calls were not considered. Around each recorder, we evaluated and analyzed environmental parameters – the presence of laying and standing deadwood and signs of logging. The presence of these parameters on at least half the sum of all points on the lines meant that the parameter was present around the line. For analyzing the impact of selected parameters (Forest landscape integrity index, Tree cover density and elevation) were used GIS layers. They were analyzed within a 300-meter buffer area around the recorders. Tree Cover Density (TCD) has been created in the frame of the tender “EEA/IDM/R0/18/009 - High-Resolution land cover characteristics for the 2018 reference year” as part of the EEA Copernicus Land Monitoring Service (CLMS, https://land.copernicus.eu).

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