Acoustic recordings and analysis
Song Meter SM4 Autonomous Recording Units (ARUs; Wildlife Acoustics Inc. ©, Maynard, MA) with two omni-directional microphones were deployed at two point count sites per habitat (six per mountain) in both BC and Chile. ARUs were deployed at least two point count sites apart (>400 m). In BC, 36 units were deployed for 10 – 25 days on six mountains, and for 33 – 37 days on the remaining 3 mountains, between June 3 and July 15. In Chile, 6 units were deployed on five mountains for 3 – 10 days each, between November 13 – December 28. ARUs recorded at a sampling rate of 24000 Hz in stereo wav format using default acoustic gain settings for the microphones. Units were mounted on a tree several meters from the point count site, or on a PVC pipe at ~1.5 m height in the alpine. ARUs were programmed to record 30-mins on, 30-min off starting three hours before sunset, all night, and ending 5 hours after sunrise (16 x 30-minutes point counts).
Sound recordings were analyzed using Audacity® software (V2.3.0, Audacity Team, 2020). Two skilled observers reviewed all the recordings in BC and bserver did so in Chile. All observers had experience conducting point counts in the same regions. In BC, both observers analyzed five of the same recordings to confirm detection consistency. Spectrograms were scanned manually in stereo format as the observer listened to the recording. Species that were more difficult to identify were compared with recordings available on bioacoustics libraries such as the Xeno-Canto Foundation (2019) and/or sent to other skilled ornithologists.
Two (BC) or three (Chile) different days were selected for sampling per site over the season. In BC, . If a selected day had unfavorable conditions (wind or rain) that interfered with the audio, another day was selected randomly. From the 30-minute audio recorded hourly between sunrise and four hours after sunrise on these days, we randomly chose one, 6-minute interval to analyze (5 x 6-minute point counts/day). We manually analyzed 1,150 x 6-minute ARU counts.