Author Interview: Vocal communication in wild chimpanzees: a call rate study

PeerJ spoke to Alexander Piel about the recently published article Vocal communication in wild chimpanzees: a call rate study. Alexander is a lecturer in Anthropology at University College London, and director of a long-term primate project in the Issa Valley, Western Tanzania.


Can you tell us a bit about yourself?

I am a lecturer in Anthropology at University College London, and director of a long-term primate project in the Issa Valley, Western Tanzania. I studied Animal Behaviour as an undergraduate and then Anthropology for Masters and PhD work. Early on I contracted the ‘savanna-chimpanzee’ bug, which led me to work in SE Senegal and then Western Tanzania – two of the driest, most open habitats that host chimpanzees. Most of what we know about chimpanzees stems from forest-dwelling populations, but it’s now clear that some of the most profound transformations in human evolution – becoming bipedal, an increase in brain size – first occurred in more open, mosaic habitats. With Fiona Stewart and colleagues, we initiated the current project in 2008 to better understand not just chimpanzee, but broader primate behavioural responses to living in these mosaic systems.


Can you briefly explain the research you published in PeerJ?

Chimpanzees produce loud calls – pant hoots – that travel multiple kilometres, and serve a variety of functions, from coordinating reunions between individuals or subgroups, to alerting others to high quality feeding trees. Whilst there has been extensive research into these calls – their use, meaning, and even acoustic parameters – there has been almost nothing described about the rate at which they call. This ‘call rate’ is critical for acoustic monitoring of chimpanzees, where scientists deploy remotely sensing microphone units to monitor animals that they cannot follow or see. From their call patterns, we can calculate population density and ultimately, estimate the population size….but we need the call rate!


What did you discover and where?

All data were collected by Anne-Sophie Crunchant in the Issa Valley. We found that males (adult and sub-adult) call twice as much as females, and calls were more often during nesting periods (dawn and dusk), as well as produced from woodland vegetation, compared to closed riparian forests. Issa chimpanzees also called about half as frequently as forest-dwelling chimpanzees from Tai Forest in Ivory Coast.


What was significant about your findings?

We expected males to be more vocally active and for the peak calling periods to be early and late in the day – both of those patterns are consistent with what has been described from other communities. We were surprised by the preference for open habitats when these calls are made, which could be due to sound transmission, e.g., calls will travel further through open vegetation than in forests, where soundwaves attenuate. We were also struck by the lower rate of calling compared to Tai. With a lower population density, and a far larger home range, we expect Issa chimpanzees to rely more on these calls to coordinate movement…and thus call more often. That doesn’t appear to be the case. Perhaps Issa chimpanzees are more cohesive and not separated in sub-groups as much? We have much to learn still!


What kinds of lessons do you hope your readers take away from the research?

Sometimes the most obvious behaviours still need investigation. Chimpologists have known about pant hoots since the apes were first observed, but increasingly, conservationists and field primatologist alike aim to minimise our footprint when establishing conservation priorities, assessing population health and size, etc. Acoustic monitoring is a reliable, non-invasive way to do that, but the increasingly statistical methods of extracting (in this case), the number of chimpanzees in an area relies on how often they call. We’ve now demonstrated how to do that and produced a figure that is applicable for population assessments. In so doing, we’ve also provided a model for how this same approach could be used with other loud calling animals, like elephants and lions, both also loud calling, endangered species.


How did you first hear about PeerJ, and what persuaded you to submit to us?

One of the most transformative papers in our field described using mobile phone networks to study wildlife acoustics…and it was published in PeerJ. Since then, this journal has been one in which we’ve sought to publish, especially when we finally had data on related study of animal vocalisations. More, our data are collected from Tanzania and local universities don’t necessarily have subscriptions to many of the other platforms for research, so Open Access allows Tanzania’s future primatologists to read about the work that we’re doing with local wildlife.


Do you have any comments about your overall experience with us?

Extremely positive, efficient, and helpful, from reviewers to editors. Splendid.


Would you submit again, and would you recommend that your colleagues submit?

Absolutely and absolutely.

You can find more PeerJ author interviews here.

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