Close up of orangutan holding onto a branch. Life Solved logo and episode title on left.

How vocalisation helped classify the world's most endangered great ape

  • 27 July 2021
  • 15 min listen

Dr Marina Davila Ross investigates communication in primates, from laughter to long-distance calls in the wild. In the latest episode of Life Solved, she explains how her data helped classify a distinct new species of great ape in 2017.

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Similar, but not the same

The Tapanuli Orangutans are the third and most endangered species of orangutan. Living in rugged, mountainous terrain in South Tapanuli, Sumatra, it was long thought that this species was the same as their swamp-dwelling cousins found in other areas of Sumatra. But the colony Marina has been studying looked different, and they sounded different too!

They have fuzzier hair and moustaches, and the females are very beardy, more beardy than the females from other areas of Sumatra.

Dr Marina Davila-Ross, Reader in Comparative Psychology

Long-calls and behavioural analysis

Behavioural analysis is an important part of understanding different species of animals. Even if they looked similar to the Bornean and Sumatran varieties of orangutan, the Tapanulis had a distinctive long-distance call that gave the game away. Twenty years ago, Marina was recording and analysing audio from primates, which help her and colleagues to eventually spot the difference.

Orangutans need to be able to identify their species through these calls. The results showed that these vocalisations are genetically grounded, and the populations also showed a pattern that matched what we knew about migration.

Dr Marina Davila-Ross, Reader in Comparative Psychology

Marina had walked and camped in forests at night to gather a range of primate calls on a high-quality Sony Walkman. This audio was later analysed as sonograms which denoted unique pitches and frequencies.

Years later, researchers used a mix of analytical techniques from different disciplines to study the Tapanulis and thanks to Marina’s acoustic data, in 2017, they were declared a distinct species. This was just in time to rescue it from potential extinction.

Protecting an endangered species

Plans had been underway to construct a hydroelectric power plant on the site the 800-strong Tapauli population called home. Once recognised as a highly endangered species, conservation took the front seat. Over a million people signed a petition of objection and authorities moved to protect the Tapanuli environment.

We have to protect these orang-utans. Without protection, it has been calculated that within seventy-five years, there will be a decline of over 80%. So it's really important to me to monitor them daily to identify forest areas that are necessary to build forest corridors and to protect more of their habitat.

Dr Marina Davila-Ross, Reader in Comparative Psychology

It’s remarkable to think how close this species came to being wiped out, but thanks to international, cross-disciplinary research between organisations like the University of Portsmouth and its partners, this precious population can live on.

You can listen to Life Solved on all major podcast players, whether via Apple, Spotify, Google Podcasts or other apps. Just search for 'Life Solved' and press the subscribe button.

Episode transcript:

Anna Rose: You're listening to Life Solved from the University of Portsmouth. This is the series where we look at how research is having an impact on our lives in real time and changing our world. In this episode, we'll learn how the sounds or vocalisations a group of animals makes can provide vital data in understanding and identifying different species. What's more, we'll hear how one researchers 20 year old Sony Walkman recordings helped in the identification of a whole new species of great ape. John Worsey interviewed Dr Marina Davila-Ross. Have you ever heard of Pongo Tapanuliensis? It's otherwise known as the Tapanuli Orangutan. It's the third of three species of orangutan and there are only about 800 in the world.

Marina Davila-Ross: So Tapanuli orangutans live in Sumatra and also in Sumatra outside of that specific area, there are other orangutans, Sumatran orangutans and then there are orangutans from Borneo. So just in these two islands, Sumatra and Borneo, orangutans exist. Until the study from2017, there has been this general idea that they are only two orangutans existing in these two different islands respectively. That absolute isolation that occurred through the volcanic eruption, but also earlier than that, about 3.5 Million years ago, there was some separation from the tapanuli and other orangutans in Sumatra.

Anna Rose: Marinas from the Department of Comparative and Evolutionary Psychology here at the University of Portsmouth and says the tapanuli orangutan is critically endangered, but we nearly didn't know this at all.

Marina Davila-Ross: The study started actually 20 years ago when Eric Maynard from the Australian National University conducted a survey in South Tapanuli near Lake Toba in Sumatra and found that these orangutans living there are isolated apart from other orangutans in Sumatra, probably as a result of a volcanic eruption that happened about seventy five thousand years ago. And they also look quite different. They had fuzzier hair and moustaches and also the females are very beardie, more beardie than the females from the remaining Sumatra and Sumatran orangutans. So there then the idea came that perhaps these orangutans are different enough so that they may be a different species. So that triggered then the idea to systematically compare it to tapanuli orangutans, so orangutans from that region, a region of South Tapanuli, with the other orangutans from Sumatra and also Borneon orangutans. The tapanuli orangutans live in Sumatra. So just in these two islands, Sumatra and Borneo, orangutans exist. So as a result of this study the IUCN, the International Union for Conservation of Nature, identified these tapanuli orangutans as critically endangered, with only eight hundred individuals making up the population. So they are the most endangered great ape species. And that received a lot of media attention and also triggered a conservation plan. Also, there was a plan to build a hydroelectric power plant and that is now being in discussion, is being re-evaluated due to a petition signed by over a million people. And that plan is now postponed for at least three years. And let's see what is going to happen. But we have to protect these orangutans at this stage. Without any protection, it has been calculated that within seventy-five years there will be a decline of over 80 per cent. So it's really important to observe the orangutans monitor them on a daily basis, to identify forest areas that are necessary to build forest corridors and to protect more of the habitat of these orangutans.

Anna Rose: The Tapanuli had also been identified in the 1930s but forgotten by modern science. Without this latest piece of research identifying the uniqueness of the Tapanuli species, this small population might otherwise be faced with a hydroelectric power plant construction that compromised their home environment. Marina first got involved with the study through her interest in the vocalisations of orangutans. The tapanulis don't exactly live in an easy to reach spot with a dense forest canopy in mountainous, rugged area, unlike its swamp forest-dwelling relatives.

Marina Davila-Ross: Twenty years ago, I conducted a study on orangutan long calls. We were interested in long calls because they are vocalisations that are produced over long distances. So orangutans need to be able to identify their own species through these calls. They are used by males in order to keep other males away. So we predicted that these calls have a genetic basis. And I conducted such a study then as part of my master's project where I had recordings from eight different populations throughout Borneo and Sumatra, obtained from colleagues and also from some libraries. But there were two populations where I didn't have data from. And so I conducted field trips in Sarawak and in Sabah, I had the chance to live for three months, which was very nice, and walk with them through the forest and camp in the rainforest and listen to the orangutan calls at night. We did not know at that time that the orangutans produced long called at night. And then we walked in the morning to try to search for these orangutans and get good recordings. So that was a very exciting time for me! Then I was lucky enough to obtain a sufficient number of recordings from Sarawak and Subba and conducted an analysis based on these 10 orangutan populations. And the results showed then that these vocalisations are genetically grounded. The recordings were matching, the populations were grouped in according to the populations, and the populations also showed a pattern that matched what we knew about the Pulo migration.

Anna Rose: That's how they realised they could use these long calls to identify different species of orangutan. Some of this data was really useful on the Tapanuli study, which led to the classification of the new species years later in 2017. It was the long calls gathered from the Tapanuli population that was crucial in their behavioural analysis.

Marina Davila-Ross: The approach would be not just to look at genetics, of course, but also to look at morphological features and acoustics, and to examine the data across all of these levels, and to see whether they were matches and whether there was a distinction between the Tapanuli orangutans and the Bosnian and Sumatran orangutans. The acoustic part was where I contributed to. But this was a very large research team led by Ericsson and Nature from the University of Zurich, and a huge research team of researchers from different disciplines and all joining forces together to conduct the study, which was really important because obviously, we needed data from these three different groups of orangutans, but also across these three levels; genetics, acoustics and also morphological data. [LONG CALLS]. These calls are quite difficult to produce. They are very loud. They carry over a kilometre. They can be heard from such a long distance and they are probably very difficult to produce. They are linked to the very huge orangutan males with these large cheek pads to keep distances from other males. The long call consists of wars and Wheatus in the middle. I call them Wheatus. I don't know how else to call them because they sound so unusual. They sound like whe-tu. Then they speak a rise. They have also babbling sounds at the beginning and the end of the call. And there are some sighs. So that's the rough structure. But what we found was just two sounds produced at the same time. So one of them is most likely produced by the vocal folds in the larynx, moving in a synchronised way. And perhaps there are some other folds in mouth cavities or so that can be used. The orangutans have huge throat sacs, so perhaps something there can be used in order to produce sound waves.

Anna Rose: Marina explained how you go about analysing such sounds.

Marina Davila-Ross: The typical way would be to examine it via a sonogram. That's what I did most of the time for measuring these orangutan long calls. And so the sonogram is a picture that shows the frequency on the Y-axis and on the X-axis there's time. And one can see if a sound is high pitch. We can see if it's voiced or if it's more chaotic. We can see also certain shapes and one can identify different call types.

John Worsey: Yes. So it's patterns that you're looking for, really, rather than you have to be able to distinguish the outliers from that and see where the real recurring patterns are?

Marina Davila-Ross: Yeah. Patterns in terms of finding commonalities, looking for commonalities and differences, and a good combination of both. The sounds were collected twenty years ago, so it was more with analogue recorders. The high-quality professional Sony Walkman and one-directional microphone for very long distance calls. But at that time, we tried not to use digital recordings because we knew that they would manipulate to some extent the sounds  compress the sounds.

Anna Rose: Well, times may have changed with the technology available, but when it comes to gathering data in the field, Marina always has to be careful not to influence the situation with her own presence.

Marina Davila-Ross: It's always really exciting to record these vocalisations. It's just a very nice experience. And probably this specific call was that I got a little bit too close to that male and it's really difficult to find the right distance where you still keep a distance but get a good quality recording. So I remember that I noticed that I was a little bit too close to him. I was about 50 metres or so away and he started to produce his call. And I remember that it was, yeah, just very exciting to be there. And there were lots of mosquitoes biting me around that time. And I also hope that the call would not be so long.

John Worsey: What's the danger of you being too close? Is it that they might actually become aggressive in protecting their territory?

Marina Davila-Ross: So these were orangutans that were not habituated to humans. So typically they would not attack humans. They would keep their distance. My method was to really just get slowly, closer and closer and be able to get lots of recordings throughout the day and not to disturb the animals. And I also didn't want to instigate cause. I didn't want to have an impact on the vocalisations because perhaps they would produce these vocalisations a little bit differently as a result of me being there in comparison to another orangutan being there.

Anna Rose: Marina explained how her general research interest led her to the tapanuli study. She's looked at topics such as the evolution of laughter and infant communication.

Marina Davila-Ross: My main research focus on the communication of great apes. I also studied chimpanzees and orangutans primarily, but also other great ape species. I chose these two because they are phylogenetically furthest away from humans and phylogenetically closest to humans. It gives a nice comparison. And I study chimpanzees in Zambia, the orangutans that I study live in a rehabilitation centre in the south of Borneo. It's difficult to work with animals and just focus on a topic on communication like communication or emotions without seeing the situation. And we have the knowledge and how we can apply research in order to improve certain things in a rehabilitation centre on other places and just made sense. It's just often there is not a communication between wildlife authorities and researchers. We're developing a method that helps these rehabilitation centres to more quickly identify strong candidates for releases. So when these rehabilitate animals are being released into the forest, they face a lot of challenges. Of course, a very different situation. So with this method, we can identify stronger candidates but also identify skills that need to be improved. And when is the best time to release an individual?

Anna Rose: Marina now hopes much more can be understood by research into this precious Tapanuli population.

Marina Davila-Ross: It's too early to say, but they're likely to be really interesting to study. So if they're genetically grounded differences, one wonders why this is the case. So we look at the long calls they produced particularly long duration. Why do they do that? And why are the pitches higher? Does it have something to do with the ecology? Does it have something to do with the interactions with other males? There's a lot of potential there in studying them just from a behavioural perspective.

Anna Rose: Next time on Life Solved, we'll be back to find out how our work is helping catch perpetrators and tackle wildlife crime in the field.

Nick Pamment:: When pangolins feel threatened, they'll curl up into a ball. So they are very easy to take from the wild. The scales ground down are used in traditional Chinese medicine and their meat is also used. It's an awful, awful situation the pangolin finds itself in.

Anna Rose: You can find out more about the University of Portsmouth Wildlife Crime module and more of our research at You can follow this podcast on your favourite app and share it on social media using the hashtag Life Solved.

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