In the wild, small birds respond to their predator, the Eurasian Pygmy Owl Glaucidium passerinum, with aggressive behaviour, i.e. mobbing. We aimed to determine the specificity of response rate of the forest birds to the broadcast vocalization of the Eurasian Pygmy Owl comparing between areas with and without the owl presence. We compared species structure of mobbing birds taking into account their numbers and seasonal changes in the response rate. In addition, we wanted to assess the reliability of estimating the presence of the Eurasian Pygmy Owl by recording the response of mobbing birds. Filedwork was carried out at Mt. Jelovica, where the Eurasian Pygmy Owl is present, and in the lowland forest near Brnik, which was the control area without the owl. We broadcast the playback of the Eurasian Pygmy Owl male song on multiple sites in the area in the morning and observed the response of the birds. We found that mobbing response is species-specific and locally specific, since birds responded only in the areas with the Eurasian Pygmy Owl being present. Mostly the species that represent the potential prey of the owl responded, in addition to adult specimens, young specimens are also involved in mobbing. In autumn, the response of birds was more intensive, with the birds responding in much higher numbers than in spring. Because of the specificity, the mobbing response of the birds could be used as a reliable indication of the presence of the Eurasian Pygmy Owl in a particular area.
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