Page 187 - Demo

Proceptive vocalisations in orang-utan females1858showed responses similar to the day before when we played long calls, including vocalisations, but showed no discernible behavioural response when we played a control sound. Crucially, she quickly approached the source of the stimuli and emitted vocalisations in response to calls, but never to control sounds.On the afternoon of day 2, we wanted to continue the experiment by playing more stimuli to Temmy. In this case, we played two long calls and two control stimuli. Similar to before, she did not respond to the control trials. However, her behavioural response to the long calls was completely different from this moment onwards. While she did still look into the direction of the speaker during the stimulus playback, she did not approach it like before, nor vocalise. In the next two days, we played three more long calls and three more control stimuli, but Temmy did not respond like she did on day 1 and the morning of day 2 anymore.The change in behavioural response that we observed suggests that Temmy only showed proceptive behaviour in response to the calls during her periovulatory phase. Given that this phase lasts about 5 days, this fits well with the fact that Temmy and Mr. Miyagi mated two days prior to the study period. However, another explanation would be that Temmy habituated to the stimuli over time, even though this would not explain why she did not show a similar response to the control stimuli. Still, we went back 2 months later to test this alternative hypothesis.Figure 2. Description of the behavioural responses of Temmy to the long call stimuli on day 1 of the first study period. The white bar represents the duration of the stimulus playback, while the shaded bar represents the post-stimulus period. The area between two thick black lines represent one minute.Tom Roth.indd 185 08-01-2024 10:42