Page 184 - Demo

Chapter 8182this part of the cycle lasts approximately 5 days, similar to humans (Kubatova & Fedorova, 2016).StimuliThe long call recordings that we used for the playback experiment were collected at Sikundur Research Station (Sumatra, Indonesia) by James Askew (Askew, 2019). From all the recordings, we selected only calls classified as “spontaneous”. As control sounds we used two calls of the Great argus pheasant (Argusianus argus), a bird species that occurs in the natural habitat of orang-utans. We edited all stimuli to last 45 seconds so that each stimulus had the same duration. Furthermore, all recordings were normalized so that the volume level was similar across stimuli. Design of trialWe made audio recordings of the vocal response using a Sennheiser ME 67 microphone and a Tascam DR-40X recorder. Two camcorders (study period 1) or one camcorder and one action camera (study period 2) were used to videorecord the behavioural response to the stimuli. To play the stimuli, we used a custom loudspeaker linked to a Marantz PMD 620 unit. We played the stimuli at ±90 dB at 1 m from the loudspeaker.The setup of our study was in line with recommendations (Fischer et al., 2013): while one researcher was responsible for placing the speaker and playing the sound, one or two other researchers videorecorded the response. In addition, one of the researchers carried the microphone that was used to record Temmy’s vocalisations opportunistically. Before starting a trial, we would first identify Temmy’s location. After that, we would determine a suitable location for the speaker. We did not want the speaker to be clearly visible to Temmy at the onset of the trial. After we chose a location for the speaker, we would start the stimulus playback of 45s and immediately videorecord her response. We would continue videorecording her response for a few minutes after the stimulus ended, and would stop when her behaviour seemed to be back to baseline (ie., when she displayed no more intensely proceptive behaviours and/or stopped vocalising). EloiseData for the second case were obtained from Los Angeles Zoo (LA, California, United States). This case concerns Eloise, a Bornean orang-utan female who Tom Roth.indd 182 08-01-2024 10:42