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Summary

  • The initial submission of this article was received on February 23rd, 2018 and was peer-reviewed by 3 reviewers and the Academic Editor.
  • The Academic Editor made their initial decision on March 27th, 2018.
  • The first revision was submitted on May 2nd, 2018 and was reviewed by 2 reviewers and the Academic Editor.
  • A further revision was submitted on June 3rd, 2018 and was reviewed by the Academic Editor.
  • The article was Accepted by the Academic Editor on June 4th, 2018.

Version 0.3 (accepted)

· Jun 4, 2018 · Academic Editor

Accept

Thank you for further revising your manuscript. I am now happy to accept it.

# PeerJ Staff Note - this decision was reviewed and approved by Jennifer Vonk, a PeerJ Section Editor covering this Section #

Version 0.2

· May 30, 2018 · Academic Editor

Minor Revisions

You have taken care of most of the reviewers comments but there are still some minor comments. As you will see especially reviewer 3 raises an important point about a potential mismatch between the abstract and the text which was mentioned before but needs to be addressed further.

·

Basic reporting

I am satisfied the authors addressed the previous comments and points made on basic reporting.

Specifically the title now better reflects the topic of the article, with the alpha takeover being included. One further, small suggestion here would be to include ‘…affects variation in the acoustic properties of male chimpanzee loud calls’. However if you feel this makes the title too long (and only adds slightly to clarity), then please ignore.

Thank you for clarifying which data were collected through focal follows, and which ad libitum. It is helpful to have these separated in Tables 1 and 2. Including more details on leaf-clipping behavior in this group (and surrounding groups) before and after the study period gives the findings a little more context in terms of the types of conditions under which leaf-clipping emerges, and I think this has improved the flow of the ‘story’.

Some minor points on basic reporting on the new version of the manuscript:

I’m glad to see you have changed the transition between paragraphs on lines 88-89, however I wonder if it could be smoother by starting the next paragraph (line 89), with something along the lines of ‘As well as buttress drumming, several other gestural signals have been observed to be produced in conjunction with chimpanzee pant hoots. In the Tai forest in Cote d’Ivoire, the chimpanzees will occasionally ‘leaf-clip’…’ (or something similar to what Reviewer 3 had previously proposed).

Line 102 could be read to suggest that signals with limited temporal overlap are ‘free’ multimodal signals. Perhaps this sentence could be restructured to say ‘…example of multisensory communication in chimpanzees, also referred to as a ‘free’ multimodal signal (), albeit with limited temporal overlap between the two signals in this case.’

Lines 159-162 would be more clear if rephrased to ‘…before the start of a pant hoot. Soft, intermittent ‘hoos’… leaf clipped (Video S1), however only if these ‘hoos’ graded into the start of a pant hoot (<3s) were they considered part of the pant hoot.’

Line 272 – instead of saying ‘We tried to include behavioural activity…’, it might be better to say ‘We first included behavioural activity…led to model instability’

Experimental design

The continuous calculation of dominance ranks is now explained in greater detail, which is helpful for the reader.

I am happy with your justification of not including behavioural context in the models due to fear of destabilizing them too much, however I’m a little confused as to whether Table S1 and/or Table S2 include behavioural context. You mention in your response that Table S2 shows full null model comparisons including behavioural activity, and lines 198-199 explain why behavioural activity was not included, then saying, ‘but see Statistical Analyses and Table S1’. However I can’t seem to find anything in either table relating the activity as a control… though I think it might be that this is clarified in the table heading/descriptions(?), which I seem to be missing.

Thank you also for including a short paragraph on the reasons for including drumming as part of the climax phase. I expect some researchers may disagree that it is truly a part of the pant hoot itself, as opposed to a separate behavior that simply frequently co-occurs with pant hoots (such as swaying during the build-up, branch shaking etc.) but I think this is reasonable, and useful for future researchers to take into consideration (/fuel debate).

Validity of the findings

The authors made changes in line with previous suggestions. I agree including the more detailed analysis on why Romario might have started leaf-clipping at the point at which he did would be unnecessary.

I still feel the first sentence of the conclusion could be stronger, as the summarised conclusion that leaf-clipping combined with pant hoots are associated with an overall conspicuousness of pant hoots is a little unclear as a take-home message. ‘Conspicuousness’ is quite vague, and not really mentioned in the rest of the manuscript. But perhaps changing this to ‘associated with increased conspicuousness…’ would at least give some indication of the direction? Or something more similar to the first line of the discussion.

·

Basic reporting

I have no new comments in this section, but want to refer to a previous comment:

MY ORIGINAL COMMENT: "Related to one of the major issues, the abstract indicates the mismatch between the information provided there and the conclusions of the manuscript. In the abstract, the authors write “We suggest that elevated arousal and aggression during the alpha takeover triggered the re-emergence of leaf clipping and the associated acoustic changes in pant hoots.” In the main text, however, this issue is raised only in the final paragraph. Although it is claimed that arousal seems a less likely explanation, the sudden re-emergence of the leaf-clipping behavior, the more frequent and longer pant hoots along with the other changes of several acoustic parameters and the increased rates of buttress drumming seem to be closely related to the increased levels of arousal caused by the instability of the group. I am not suggesting that this might be the only explanation, but I think it is a very likely one and should be considered to a much greater extent than it currently is."

THE AUTHORS' REPLY: "We understand the mismatch described by the reviewer. We have kept the sentence in the abstract as is and in the discussion we now present the arousal explanation earlier and before discussing other alternatives (2nd paragraph of Discussion). In addition to removing some aspects of the old discussion that were distracting, we hope the reviewer finds these changes agreeable."


MY NEW REPLY: I am afraid I am still not convinced by these changes, not content-wise, but in terms of the coherence of the results’ interpretation. Yes, the discussion now earlier refers to displacement behavior caused by stressful situations. However, you conclude that “…displacement behaviours in animals are usually more self-directed, such as scratching or self-grooming (Maestripieri et al., 1992), and this would not explain why leaf clipping was specifically coupled with pant hoots.”. Furthermore, in the final section of your discussion, you are still writing that it is “…difficult to assess how much of the acoustic variation observed in pant hoots preceded by leaf clipping can be attributed to greater arousal alone. However, according to Morton’s motivation structural rules (Morton, 1977) we do expect lower fundamental frequencies when animals signal aggressive intent which is supported by our results.” If I understand this correctly, you doubt that arousal is the main explanation for the re-emergence of leaf-clipping. However, in the abstract, you “…suggest that elevated arousal and aggression during the alpha takeover triggered the re-emergence of leaf clipping and the associated acoustic changes in pant hoots.” So, I hope I do not understand this incorrectly, but I cannot see a coherent line of argumentation regarding the contribution of arousal for your observed behaviors.

Experimental design

I have comments.

Validity of the findings

I have comments.

Additional comments

This manuscript has been properly revised and the reviewers' comments have been considered/incorporated thoroughly.

Apart from my comment in the "Basic reporting" section, I have no additional comments, apart from some minor issues:

Some typos:
- lines 72, 83: please add commas after )
- line 264: please remove space after )
- Line 283: insert space after ).

Version 0.1 (original submission)

· Mar 27, 2018 · Academic Editor

Major Revisions

As you will see all three reviewers have several comments that they would like you to address. Some more major than others. I agree that the introduction could be clearer and you could potentially restructure in line with the reviewers comments to make it easier for the reader to understand what the focus of the study is.

I also noticed that while you provide the raw data you seem to not have included the focal ID so it would be impossible to run the statistics again. You might want to double check that.

·

Basic reporting

This describes the re-emergence of leaf-clipping, a behaviour previously described in this population in combination with pant-hoots, during a period of instability. The authors provide a detailed account of the re-emergence of the behaviour, its transmission, and the associated variations in acoustic parameters of the pant-hoots. The rarity of the events described in the paper make it interesting and valuable.

Given the focus on the combination of leaf-clipping and pant-hoot in a multimodal display, I think the introduction would benefit from including a brief review of the literature on multimodal communication in primates and other animals. This would help the reader to understand the aims and predictions.

Overall the paper is nicely written and complete. The figures and table are informative.

Experimental design

The design of the study is clear and straightforward. The research question is clearly defined and addresses a rare aspect of chimpanzee behaviour that has received little attention so far.

The methods used seem appropriate, but more details are required at times. Specifically, it would good to explain why separate models were built for each acoustic parameter measured rather than using factors of correlated measures, as the authors have done in the past (e.g. Kalan et al. 2015).

I also think that the analysis of the dominance hierarchy is not transparent enough. There aren't any details about how the rank of each individuals were obtained. I suggest the use of Elo-ratings (Neumann et al. 2011; R package: Neumann & Kulik, 2014), which is suitable for analyses of changes in short intervals and provides a quantitative measure of social stability.

I am not an expert in acoustic analyses, but they seem to have been conducted adequately.

Validity of the findings

The analyses seem appropriate, although the number of males in the group is small, appropriate measures have been taken to ensure the validity of the analyses. The conclusions are well stated, and although I am not totally convinced by some of the interpretations, they remain possible and the authors are cautious.

Additional comments

See annotated pdf for detailed comments.

·

Basic reporting

The authors documented the re-emergence of a gesture which had not been observed in this chimpanzee community for several years, and made use of this valuable opportunity to investigate how the acoustic properties of pant hoots (well-explored loud call of chimpanzees) might be altered when preceded by the leaf clipping gesture. Furthermore as this re-emergence accompanied an alpha take-over within the group, the authors recognised the importance of also investigating the effects of this instability (within the dominance hierarchy) on the acoustic parameters.

Collecting data during rare circumstances such as these is incredibly valuable in helping us to understand the possible conditions which may lead to the emergence of specific behaviours/signals. This is especially so for behaviours which are seen relatively rarely and appear to have different cultural variants – such as leaf clipping.

The manuscript is well-written, well-structured, easy to follow, with clear and professional language used throughout. Background literature on pant hoots and leaf clipping provided the necessary context to set up the hypothesis and predictions. Tables, figures, supplementary material and raw data are provided and appropriately referred to in the text. Table and figure headings/titles/axes are generally labelled with sufficient detail to enable the reader to understand the data displayed.

A few minor comments on basic reporting:

1) I was surprised that the title does not include anything relating to instability in the hierarchy/the alpha take-over, as this is featured in the article in equal measure as leaf clipping
2) Throughout I was sometimes confused as to which data came from the focal follows, and/or were collected ad libitum. On Table 1 it appears that aggression numbers are based on focal follow data – however leaf clipping and pant hoots were collected ad libitum (although there was also focal data available?). On line 349 and 382, you mention pant hoot rates – here it would be important to make sure to note that these rates are presumably derived from focal follow data only, or otherwise explain how these were calculated
3) Similarly it would be useful to clarify whether ‘Number of aggressive interactions’ refers to instances when the individual was the aggressor OR victim (i.e. involved in any kind of aggressive interaction), or whether these were only the instances where the individual was the aggressor. Lines 259-260 would suggest the latter – this should be reiterated for the relevant tables (Table 1, Table S1), as otherwise this phrasing can be somewhat ambiguous/misleading
4) I would be really interested to know how common leaf clipping was before the respiratory outbreak – and whether it was also mainly observed before pant hoots. Equally I was wondering whether this was the first alpha take-over since the outbreak, or whether there had been others which had not triggered the reappearance of leaf clipping. If you have this information available, even just from personal observation or communication, it would be nice to include to complete the picture a little more.

Experimental design

The research focus and predictions were clearly defined, and sufficiently backed up by relevant material covered in the Introduction. It is evident how this research addresses a gap in our existing knowledge of this behaviour. Observational focal follows, in addition to ad libitum data collection, and pant hoot acoustic recordings are a suitable means of addressing the research goals here.

The definition of ‘during’ alpha take-over is also very clear, and a good measure of when the instability among the males is likely be at its highest.

I have a few comments and suggestions for clarifications in terms of experimental design:

1) More detail could be included on the specific method of calculating dominance ranks from pant grunts (e.g. lines 138-141). Also whether rank was assessed/calculated every few months, or continuously – as it seems that for most of the males the rank changed during the 11 month study period
2) It would have been nice to take the behavioural context of the pant hoot into account as several of the studies cited have shown that context has an impact on acoustic properties such as fundamental frequency (e.g. Notman & Rendall, 2005; Fedurek, Zuberbuehler & Dahl, 2016) – hopefully future research can explore this.
3) I was not aware that the climax phase could consist purely of drumming, with no vocal elements (lines 178-179) – it would be good to cite a relevant paper here where the climax has been defined like this before, or to provide a justification for defining it in this way.

Validity of the findings

The manuscript is very thorough in explaining how the acoustic parameters were extracted using Praat, and I found Figure 1 very useful in depicting this.

It is easy to understand that several acoustic variables were investigated as response variables (Table S2), and these have shown variability in the past – thus being appropriate when the aim is investigate variation in pant hoots. Equally the fixed effects are intuitive and directly addressing the hypothesis.

The statistical analysis is incredibly comprehensive, and the results are then also explained in more easy-to-digest terms – making clear what the main and most important findings were. Table 2 is especially handy in showing the contrasting effects of instability and leaf clipping on the response variables.

A few comments on the findings:

1) The findings on leaf clipping are fascinating – however perhaps somewhere in the discussion it would be good to underline the fact that this gesture is nevertheless very rare (only seen 36 times in 11 months), and the vast majority of pant hoots are still produced without being preceded by this
2) I am intrigued as to why Romario started leaf clipping at the point when he did (several months after the alpha and beta, line 287) – if you have any speculations as to why this might be then this could be an interesting point for the discussion
3) It would be worth mentioning the potential role of social learning in the spread of this gesture (e.g. with reference to other gestures shown to have cultural variation and the possible influence of social learning in these – for example grooming hand clasp), especially if all males have now been observed to leaf clip (lines 433-435).
4) I found the first sentence of the conclusion (lines 430-432) a little vague – I would rephrase ‘associated with an overall conspicuousness’, or simply state that several acoustic properties were significantly impacted by the occurrence of leaf clipping before the pant hoot, then going into specifics in the next sentence.

Additional comments

Additional minor comments:

- Line 25-26: ‘leaf clipping… almost always preceded a pant hoot vocalisation’ – this might be better rephrased to something like ‘leaf clipping was observed almost exclusively immediately prior to pant hoot vocalisations’ – as otherwise could be misread to be stating that almost all pant hoots were preceded by leaf clipping. This is a very minor comment – but something that threw me off on the first read.
- Line 28: ‘affecting variation in loud calls’ – if space, I would say ‘ affecting variation in the acoustic properties of loud calls’
- Lines 35-37: I think this sentence is less important and could potentially be cut – it is generally well-documented that pant hoot and aggression rates will be high during high male-male competition. Equally if leaf clipping typically occurs before pant hoots it is not surprising that it is more likely to be observed on days when there is a lot of pant hooting. This is also mentioned again on lines 367-368.
- Lines 61-62: extensive list of primate studies, and then the next sentence covers primates again. Perhaps it would be possible to combine them – also because the term ‘primates’ is used before it is noted that ‘primate’ will be used to refer to NHPs.
- Lines 112-115: could be explained more clearly why leaf clipping males were predicted to produce pant hoots with lower F0, longer duration etc.
- Line 118: ‘a critical social context for signals associated with male loud calls to be modulated, including pant hoots’ – this seems a bit circular when reading, as male loud calls are pant hoots… maybe rephrase for clarity.
- Line 140: I suggest modification ‘pant grunt is uniquely produced towards more dominant individuals’, or something similar which makes it clear that they would not be produced e.g. from alpha to beta (who is also a dominant individual)
- Lines 165-166: at this point it has not yet been explained that you will only be looking at three (of the normally four) phases – this is only mentioned on lines 175-177. Maybe mention briefly or already explain fully here.
- Lines 181-183: ‘as well as drumming’ – clarify here whether drumming is included or excluded for the durations. Could be re-written as ‘Durations were measured for the total pant hoot and for each of the three phases as well as the drumming bout, excluding any leaf clipping, if it occurred’.
- Lines 187-188: I would think it would make more sense to describe which call was chosen in the event of an even number of calls.
- Lines 284-285: I think this sentence is unnecessary – Table 1 shows that ‘after’ instability three of the males were leaf clipping (not all five), and these cases are already explained.
- Line 340: be clear as to what is meant by ‘instability period’, and what this is being compared to.
- Line 397: needs full stop instead of comma
- Lines 407-410: explain more explicitly how it is relevant that another party is still in vocal reach. The previous sentences talk about leaf clipping being a potential attention grabber; however it is difficult to follow how this might still be the case over a longer distance.
- Table 2: rephrase ‘full null model comparison’. Perhaps ‘full versus null model comparison’
- Figure S1: X-axis might be more accurate as ‘Standardised male rank’

·

Basic reporting

Related to one of the major issues, the abstract indicates the mismatch between the information provided there and the conclusions of the manuscript. In the abstract, the authors write “We suggest that elevated arousal and aggression during the alpha takeover triggered the re-emergence of leaf clipping and the associated acoustic changes in pant hoots.” In the main text, however, this issue is raised only in the final paragraph. Although it is claimed that arousal seems a less likely explanation, the sudden re-emergence of the leaf-clipping behavior, the more frequent and longer pant hoots along with the other changes of several acoustic parameters and the increased rates of buttress drumming seem to be closely related to the increased levels of arousal caused by the instability of the group. I am not suggesting that this might be the only explanation, but I think it is a very likely one and should be considered to a much greater extent than it currently is.

The second major issue is that the focus of this manuscript and the issue the authors really wanted to tackle did not become clear. The manuscript seems to meander around many different aspects of chimpanzees’ social behavior and their communication, but although the authors describe a precise research question, I found the way it is “framed” and derived from existing studies rather confusing. For example, although the title directs the readers’ attention to the re-emergence of the leaf-clipping, most of the introduction focusses on the vocal behavior of chimpanzees, with leaf-clips only mentioned for the first time in line 88. Furthermore, the authors introduce the source-filter theory and that based on this, “larger males are expected to produce lower pitched calls, which represent reliable cues of their body size and competitive strength”. Then they continue that for nonhuman primates, findings are rather inconsistent, with some studies showing that male quality is associated with low fundamental frequencies, while others found higher fundamental frequencies. At this point, I wondered whether this study aimed at contributing to this debate – which turned out not to be true. In other words – after reading the introduction, and even more so after reading the discussion (and conclusion!) of this article, I was simply not sure anymore what exactly the authors want to tackle. Was the aim to investigate whether the combination of pant hoots with the leaf-clipping display increases the quality of the males’ signaling and whether this influences their (future) position in the hierarchy? Or was the focus on the impact the males’ signaling might have on the audience, depending on whether pant hoots are produced in isolation compared to when they were produced in combination with leaf-clipping? Or alternatively, were the authors interested in whether preceding leaf-clippings modify the acoustic parameters of the following pant hoot? None of these questions was explicitly asked, but as the introduction covered many different aspects, not all of them relevant for answering the research question, it was difficult to understand the focus of the study.

Can you please specify a bit more what exactly defines “male quality”? You link this to body size and “competitive strength”, but what does the latter mean? Is this limited to physical strength and therefore the likelihood of winning a fight and/or becoming a high-ranking individual? In defining male quality, are other measures considered, such as the number of alliances/support from others or the number of offspring sired? For this study, I think this is not necessarily required, as these are most likely not measures that can be linked to acoustic parameters of pant hoots. However, how male quality is conceptualized in this study and what aspects it includes – and which not – is not fully clear.

Minor issues:
Leaf-clipping as a “socio-cultural trait”: This is already mentioned in the title and raises expectations which seem not really related to the aims of this study. I recommend not using the term “socio-cultural trait” as it is not related to any claims made by the study. The underlying mechanisms of how leaf-clipping is acquired and how it spreads across group members is (to my knowledge) not entirely clear. In this study, no claims are made in this regard, and the sudden re-emergence could be “merely” explained by the increased level of arousal. Therefore, linking leaf-clipping with this label does not contribute to explaining the current findings. If the authors want to use the term, I suggest rephrasing this a bit and to state clearly that other studies found leaf-clipping to be a socio-cultural gesture, while this cannot be concluded from the current study.

In general, I think the title might be somewhat misleading, as a large portion of this study was on the acoustic variation of pant hoots, and the relationships with leaf-clipping seemed to be a more secondary aspect.

Line 88: “Here, we documented the re-emergence of the leaf clipping gesture…”: This paragraph needs a somewhat smoother transition, as the previous paragraphs only introduced pant-hoots, so this sudden transition to leaf clipping comes as a kind of surprise. I suggest something along the lines “In addition to vocalizations like pant hoots, chimpanzees also use rich gestural repertoires. One type of gesture is the leaf-clipping signal, which re-emerged….” (or something similar)

Line 127: “The sub-adult males were included in the study once it became clear they held important rank positions in the chimpanzee hierarchy due to…” Can you please specify what “important rank positions” means? Does this exclusively refer to high rank positions?

Line 157: “Pant hoots were recorded while chimpanzees were feeding or arriving at feeding tree (n=42), resting (n=46), or traveling (n=124). For this analyses we did not distinguish between each of these contexts due to the lack of sample size per individual per category and because it was not directly related to our hypotheses.” You mentioned earlier that you were interested in how pant hoots change/are related to male-male competition. But these contexts (feeding/resting/traveling) are not related to male-male competition to any larger extent? Can you please explain why you think uttering pant hoots in such situations is somehow linked to competition/rank changes between males? Furthermore, please correct “this analyses” into “these analyses” or “this analysis”.

Line 69: “…‘pant hoot’, is acoustically sexually dimorphic…”: Does this mean they are structurally dimorphic or in terms of their usage (as the features that are mentioned seem to relate largely to the usage of such calls)?

Figures: The legend for Figure S1 seems to be missing?

Line 376: “Nevertheless, the results of Fedurek and colleagues (Fedurek, Zuberbühler & Dahl, 2016) who found rank related information encoded in pant hoots of another chimpanzee subspecies, strengthens our findings that pant hoots may contain some information relevant for male-male competition.” I found it difficult to accept this interpretation of your findings, given that rank seemed to have no effect on the patterns of changes found in the vocal behavior of chimpanzees. Can you please justify your conclusion in some more detail?

Line 391 “However, it is clear that leaf clipping before a pant hoot usually necessitates individuals to stop moving for a few seconds up to a minute (pers. obs.) before vocalizing which in itself could help to conserve some energy and rest the respiratory system right before producing the loud call and buttress drumming.” This aspect seems not really relevant for explaining the current findings?

Keywords: I suggest adding “chimpanzee” and removing “multimodal communication”

Line 173: “The pant hoots were visually separated into the introduction, build-up and climax phase that are well described and easily discernible (Marler & Hobbett, 1975; Mitani & Brandt, 1994; Crockford et al., 2004; Notman & Rendall, 2005) .” Please delete the space before “.”

Please check spelling of some references:
Barelli C., Mundry R., Heistermann M., Hammerschmidt K. 2013. Cues to androgens and quality in male gibbon Songs. PLOS ONE 8:e82748. DOI: please change Songs into songs

Fedurek P., Donnellan E., Slocombe KE. 2014. Social and ecological correlates of long-distance pant hoot calls in male chimpanzees. Behavioral ecology and sociobiology 68:1345–1355: please change Behavioral ecology and sociobiology into Behavioral Ecology and Sociobiology

Experimental design

Experimentally and in terms of analysis, I think this study has been conducted rigorously and to a high standard. Methods have been described clearly with great detail, and statistical analyses are conducted at a very high level. Therefore, I have only few comments/questions.

Line 206: “Before fitting models, the value for male rank was standardized to range from 0 to 1 to correct for the number of males in the group” But how did you take into account that the males’ ranks changed across the different phases of recordings (before, during, after rank changes)?

Furthermore, the observation periods were not really balanced regarding the total number of observational hours (237 hours before, 76 hours during, and 353 after the instability). Was this considered in the analysis?

How did you determine that rank changes were “completed” – only based on the direction of pant-grunts (with the previous alpha-male suddenly directing this vocalization towards the previous beta-male?)?

Validity of the findings

I have some remarks about the conclusions of this study:
Line: 396: “…by combining the gesture and pant hoot into a more complex multimodal signal.” I think it is important to not confuse a multimodal (or better: multi-component) signal wit sequences consisting of several signals of different modalities. Leaf-clipping followed by a pant hoot is not a multimodal signal, as both signals do not co-occur, but are separated by approx. 3 s (as described by the authors). This communicative pattern is better described as a sequential combination consisting of two signals of different modalities.

Lines 440-447: this comes rather out of the blue and I suggest deleting it, simply because this was not the focus of this paper and as I have mentioned already, this is not a multimodal signal. The observed communicative pattern does not resemble orofacial movements, as those are facial movements simultaneously combined with a vocal utterance. Therefore, this conclusion is way too far-stretched and does not follow from the data.

Is it possible to include that some information about the statistics for each of the 18 models? Also, although the raw data are provided, there is no code included (although I don’t know if this is required), so it is a bit difficult to understand how exactly analyses were conducted.

If I understand Figure 3 correctly, then the male Utan, who called most often and showed most aggression during rank instability, was the only male who was not effected by rank changes. Is there any explanation for this?

Additional comments

I have read this manuscript with great interest. It was very interesting to learn that leaf-clipping suddenly re-emerged in this chimpanzee population and that the vocalizing behavior of the males seemed to change somehow related to the changes in their rank hierarchies.

However, there are two major issues that need to be resolved, along with several more minor tasks. The two biggest problems are that first, the focus of this manuscript and the issues it is targeting are not really clear, as the introduction mentions several aspects not relevant for answering the question raised by the authors. Second, the conclusion that this observed pattern is the result of an increased arousal due to the instability of the group because of the rank changes seems much more plausible then it is currently presented (as this is only mentioned in the very last paragraph). In my comments, I explain my concerns in some more detail. Most importantly, to improve this manuscript, I suggest first, re-structuring the introduction to tailor it more to the actual research question being asked; second, to put more emphasize on the explanation that the observed communicative patterns might be the result of increased levels of arousal at the time of observations, and third, to delete some of the distracting terms, such as "socio-cultural trait", or the link to orofacial movements/theories on language evolution, as they raise the wrong expectations and/or do not really follow from the current findings.

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