Vocal activity of the Central European Boreal Owl population in relation to varying environmental conditions

Abstract

Vocal activity is one of the main attributes that enables assessment of the presence and abundance of animal populations. However, the factors affecting vocal activity are rarely studied, especially in owls. We studied the vocal activity of Boreal Owl (Aegolius funereus) using acoustic monitoring in relation to environmental factors in Central Europe (Czech Republic), over an area of 100 km2. We analysed a total of 1,310 hours of sound recordings collected over two years (2015 and 2016) at the turn of March/April and April/May. The frequency of sampling points in which we recorded Boreal Owl vocalizations varied from 0.17 to 0.59 and was higher in the year of increased prey abundance (2015) and earlier in the breeding season (March/April). The duration of Boreal Owl vocal activity varied from 1 to 60 minutes per hour and was related to temporal factors. In particular, the duration of Boreal Owl vocalization increased late in the breeding season (April/May) and in the year of higher prey abundance (2015), and it showed two peaks of vocal activity during the night.