Nocturnal soundscapes - updated version

Full description

Five non-consecutive nights were selected from each of the twelve sites (January 8th, 17th, 21st, 26th, and February 2nd of 2024) across two reserves in Australian Eucalyptus open-forest. Nights were selected based on manual inspections of the recording quality, aiming to minimize the effects of geophony (nights with calm weather conditions with minimum wind). From each night’s recording, a two-hour window was used for data extraction starting one hour after sunset to minimize contributions from dusk-active species (some of which are also diurnally active) while targeting the onset of nocturnal Orthopteran activity (crickets, katydids, grasshoppers, and locusts) during the reproductive (summer) season. Each two-hour window was segmented into 1-minute clips at 10-minute intervals, resulting in 12 1-minute clips per night, from which one 1-minute clip was randomly selected for analysis. With six sites per study area (and five nights per site), this resulted in 60 1-minute sample recordings (30 per study area) providing a comprehensive temporal and spatial coverage of the summer soundscape within the broader study region. Data quality was further improved by applying a band-pass filter to attenuate low-frequency energy (<300 Hz), reducing bias from anthropogenic noise (highway and railway). Sonotypes were manually annotated by listening to recordings and examining spectrograms within each 1-minute sample. Four taxon groups were identified: frogs, nocturnal birds, and mammals below 4,000 Hz (with only a bat sonotype annotated above 10,000 kHz); and Orthopterans (crickets, grasshoppers, katydids, and locusts) between 1,400 and 20,000 Hz (with the majority of these orthoptera calls between 3,500 to 10,000 Hz). A presence–absence sonotype matrix was compiled to assess richness (rows = site × night recordings; columns = sonotypes; 1 = detected, 0 = absent). All soundscapes present across the 60 1-minute samples were annotated and assigned to the four taxon groups (Orthopterans, birds, frogs, mammals) and to “other” (noise from anthropophony or geophony; presence– absence sonotype matrix in S1 Appendix).