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Chapter 8188in Temmy’s vocalisations. However, Temmy’s are higher in frequency (250 instead of 150 Hz) and occur in more tightly knitted sets. The lork call seems to be most similar to Temmy’s vocalisations. Both are relatively long calls (>60 seconds) with low frequency pulses. Nevertheless, the lork calls are much slower than Temmy’s vocalisations. Both the separate pulses as well as the pauses between these pulses are about double the length in the lork calls than in Temmy’s vocalisations. This means that these vocalisations of Temmy in response to the male long-call share features of some of the known calls from the orang-utan repertoire but bear no complete similarity to any of them. Temmy’s vocalisations seem to be most similar to the long-calls of male orang-utans (Figure 4). Male long calls also consist of bark-like pulses that average around 800ms each (average IOI of 1.5 sec) with a fundamental frequency of around 320 Hz. An analysis of the spectral information also shows that most of the power in these calls occurs in the same spectrum, between 200 and 350 Hz, with little to no power in the higher frequencies. With regard to the temporal structure, these calls bear strong resemblance in the sound onset timing. In addition, the duration of each pulse is similar between Temmy’s vocalisations and male long-calls. Temmy’s pulses have inter-onset-intervals (IOIs) of approximately 740ms (SD=61ms), whilst the 12 male long calls that we analysed have IOIs of approximately 800ms (SD=54ms). The clearest difference between Temmy’s vocalisations and the male long-calls lies in the overall temporal structure. Longcalls consist of rather regular repetitions of pulses that can last up to 3 minutes with steady IOIs. Temmy’s calls could also last up until 3 minutes in total, but with concatenations of bouts of 5-6 pulses, followed by a longer pause (+/- 2,5 sec.) before there was another pulse-bout. The IOIs within these bouts are similar to male long-calls, but the pauses between bouts are not typical for long-calls. To conclude, Temmy’s call seems to be most similar in temporal structure and frequency distribution to the male long-calls and less so to other orang-utan vocalisations.A second female, Eloise, proactively produced calls that also bear similarities with male long calls. Rather than the reactive calls of Temmy to long-call playbacks, this female produced long-call-like calls spontaneously. Eloise’s calls mainly differ from Temmy’s with respect to timing. Each pulse is much longer, with an average of 2.237 sec per pulse (average IOI 2.467 sec.). This makes her pulses also longer than those of the male long-call. However, unlike the concatenated pulse-bouts in Temmy’s calls, Eloise’s full calls retained a regular IOI pattern for Tom Roth.indd 188 08-01-2024 10:42