PONE-D-24-46388Contagious vocal reaction forms avian vocal exchange: an experimental study in Java sparrowsPLOS ONE

Dear Dr. Koda,

Thank you for submitting your manuscript to PLOS ONE. I apologize that the review process has been so long.After careful consideration, we feel that the manuscript has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. It will require substantial revision to be considered for publication, and will require re-review Therefore, we invite you to submit a revised version of the manuscript that fully addresses the points raised during the review process.

Both reviewers felt that the conclusions were too broad. The data are limited to one species, and the methodological issues too nuanced to conclude that avian vocal exchange operates by “a mechanism different from that of mammalian vocal exchange”. Please limit your interpretation and conclusion accordingly. 

Reviewer #1 raises various issues that must be addressed.Here is a partial list. In particular, clarify the question being tested and the exact social context in which calls were quantified. In addition, separate exchange transitions for alone vs. F2F, and clarify and account for the presence of a female bird.

Reviewer #2 suggests additional discussion of relevant literature and more conservative conclusions. Among other things, the reviewer requests clarification of how overlapping calls were assessed, and the need to compare these observations to chance occurrence.

Both reviewers list numerous specific concerns that must be addressed. Furthermore, a native English speaker should copy-edit the manuscript to correct typos and make the language clearer.

Please submit your revised manuscript by May 09 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: No

Reviewer #2: Partly

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: No

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Kikuchi et al. describe an experiment in which they examine call latency within and between Java sparrows. They claim that repeated call latency (when a bird continues calling without a response from another present bird) is shorter than similar types of intervals observed in mammals and other birds. While the use of comparative metrics is valuable, it’s unclear the extent to which these data are appropriate for their question and subsequently whether their conclusions are appropriate.

I appreciate the evaluation of how social dynamics within groups of species informs their question, but the broad generalization of the ‘fundamental difference of social structure in mammals and birds” (line 124) is quite sweeping and not testable using a single species of bird. While they compare their findings to published zebra finch data, it seems as though they’re own analyses differ significantly from those previous studies, so it is difficult to draw conclusions as to any similarities or differences between the species.

Also, it unclear as to what question(s) they’re attempting to test. Is it the calling pattern of single individual when in the presence/absence of another bird, or whether these calling patterns are fundamentally different from other bird/mammalian species? The authors should more clearly clarify the goal of their study. And, if they’re attempting to both questions, it’s not clear that they have sufficient evidence for the latter.

My main concern with the manuscript is that I’m uncertain as to what the researchers were measuring (all call intervals regardless of social context or only call intervals when in the presence of a conspecific (F2F). Several sentences are difficult to interpret and could be clarified – while these are just a few examples, there are others that may contribute to difficulty in understanding the mechanics of the manuscripts.

- Line 155: “They could usually hear and see each other”

- Line 160: “We designed the experimental space in which individual cages could be placed three-dimensionally”

- Line 189: “faced over the cage”

My understanding of the methodology is that Java sparrows called in two social contexts: alone (PRE and POST) and F2F. Total call number was greater in the F2F condition compared to the PRE/POST conditions. In addition, they measured the call interval in each of these contexts. In the F2F condition, the call interval was split into either an ‘exchange transition’ (a response to a partner bird) or a ‘repeated transition’ (the interval between two consecutive calls from the same individual).

By definition, ‘exchange transitions’ (te) can only occur in the F2F condition. However, ‘repeated transitions’ (tr) can occur in any social context. It appears the tr have all been grouped together. It would be helpful if the authors included an analysis of solely the F2F (not including any data from the PRE/POST conditions) phase. If that is what the authors did, it should be made clearer that only call intervals from the F2F phase were evaluated. Certainly, the birds must use visual and auditory cues to determine the presence/absence of another bird – the low tr interval could be explained by birds repeatedly calling in the absence of another bird in the PRE/POST conditions – the birds would not be expecting a response, so have no reason to avoid calling in a typical overlapping time interval. It would also be helpful to quantify the total percentage of returned calls – is the rate of return similar to what is observed in stranger zebra finches (Benichov et al., 2017)?

A comparison of tr in PRE/F2F/POST conditions would strengthen the manuscript to consider the effect of social context. Similarly, if the authors have video recordings of the birds, an account of whether the ‘partner’ bird is socially engaging the with the test bird, and thus, potentially more likely to respond to the test bird would also be a valuable addition. Lines 354-356 state that it’s the pseudo turn-taking data that lead to the strong suggestion that the short component identified in the exchange transition originated from the response call – the actual data from the two birds should be what leads to this suggestion because those data should and do exist.

I admit that I am not super familiar with the intricacies of GLMMs and GMMs. If the the GLMM considers the social context (alone vs. conspecific present), it would be helpful to more clearly illustrate and describe that process, along with various acronyms (e.g. AIC) that are used.

In the abstract, the authors state that the te latency is ~170ms. Nowhere in the manuscript do the authors report this result or explain its relevance (or adequately compare it to other mammalian or avian species). Similarly, they do not report a mean tr latency (for either solo vs. partner contexts) and how it compares to other mammalian or avian species (they report only that it is different – shorter).

Which bird was the female bird? While isolating a single bird’s performance in this experiment is likely not fruitful, including the female in the experiment leads to questions of whether the social dynamics between males/males and males/females is different.

I recommend several alterations to the figures to also strengthen the data presentation.

Figure 1: Include subscripts for the e and r in te and tr. Include a figure caption for 1B and perhaps an explanation for the predicted distributions.

Figure 2: Figure 2B – include a time scale

Figure 3: Indicate the female bird in Figure 3A. Figure 3B is unnecessary.

Figure 4-5: These are the critical figures. Figure 4 could be adjusted to account for ‘repeated transitions’ in the three contexts, to more carefully compare tr vs. te in F2F. (Also, is there a maximum latency in which a te or tr can occur? If so, what is the justification for those latencies?) Figures 4 and 5 could easily be combined.

In Figure 5 (according to the caption), a vertical dotted line represents the estimated values of the mean parameter in the short components). However, Table 5 (and lines 329-330) indicates negative values for those parameter estimates. It is unclear exactly what the dotted lines represent.

Lastly, the title of the manuscript is a bit odd considering that the term ‘contagious’ is not properly defined nor used until midway through the discussion.

Overall, as currently written, it is not possible to determine whether the authors conclusions and interpretations are justified due to the description and presentation of the data.

I applaud the authors for utilizing another avian species for a comparative study regarding vocal turn-taking. I also appreciate the pseudo turn-taking data as a control condition, and the inter-rater reliability metrics the authors provided regarding call classification, caller identification, and onset/offset times.

I selected, ‘No’ in response to ‘Is the manuscript presented in an intelligible fashion and written in standard English?’

While the manuscript is written in very readable English, there are enough typographical and language errors that lead to reader confusion that I suggest the authors address in future revisions.

Reviewer #2: Kikuchi et al investigate the temporal patterns of vocal exchanges in Java sparrows, with the aim of comparing communication strategies of birds to those reported in mammals. Specifically, the study aims to tests if, during vocal interactions, Java sparrows wait for a partner’s response before they produce their next call (a pattern associated with mammalian vocal turn-taking). The authors recorded face-to-face call interactions in randomized pairs of birds and analyze the temporal patterns of calls. They report that the latencies of call responses do not differ from the intervals between repeated calls of individuals. This is interpreted as evidence that birds do not adjust the timing of their vocalizations by anticipating or waiting for the responsive calls of others. Rather, in contrast to mammals, their call responses are “contagious” or socially triggered by the vocalizations of other individuals. The authors assert that these purely responsive vocal patterns correspond to the relatively fluid composition of avian social groups and aid in synchronizing flock behavior.

The study’s methods, analyses, and results are sound and generally presented in a clear, convincing manner. Some of the authors’ conclusions, however, extend beyond what was tested with their experimental paradigm, particularly in their generalization across bird species and social contexts. Nevertheless, the work presents valuable data and comparative insights from a species for which little is known regarding interactive vocal behavior. Most concerns described below can be addressed by reducing the generality of some claims and providing additional information, for example regarding the occurrence of overlaps and prevalence of repeated calls.

Comments:

1) Lines 20-22, 100-101: The authors state that no study has investigated the intervals between repeated calls of individual birds during interactions. However, intra-individual call patterns have indeed been examined in groups of zebra finches (e.g. Beckers & Gahr 2010 and Stowell et al 2016). The latter study specifically shows that temporal distributions of “self-self” call patterns (i.e. repeated transitions) differ across sexes and call types. And with particular relevance for the current study, patterns of intra-individual call timing were found to differ from responses to others (exchange transitions). “Self-partner” response patterns were found to further differentiate as breeding pairs were established. In addition to identifying excitatory influences of calls from self and others, their analyses also characterized patterns of call suppression, includes strong self-suppression, which would suggest mechanisms more complex than solely excitatory contagion.

Kikuchi et al do acknowledge that in other songbirds, familiarity and pair-bonding can affect the temporal patterns of call responses (e.g. faster, higher-likelihood responses to mates). However, since their experimental design is based on randomized, relatively brief pairings in Java sparrows, and does not take factors such as sex, call type, or affiliative pair bonding into account, the authors should be a bit more conservative with their resulting claims and predictions, rather than generalizing across the diversity of birds and social contexts: “We tentatively predict that avian vocal exchange is established by a mechanism different from that of mammalian vocal exchange in social groups - i.e. birds do not predict and wait in anticipation of vocalizations from other individuals.” (Lines 383-386).

2) The authors state that instances of call overlap are extremely rare (only 2/1712 exchange transitions), which is surprising if these birds respond to and repeat their calls with the same stereotyped intervals. It is suggested that the rarity of overlaps could be attributed to the short duration of calls. However, this finding is relevant to their claims that birds don’t anticipate the calls of others and should be investigated further. The authors should compare the experimentally observed instances of overlap to overlap rates that would be expected by chance (based on shuffled or simulated data with the same call rates). If short call durations can indeed explain low instances of call overlaps, this may suggest that Java sparrows simply lack the need for anticipatory mechanisms seen in other species with longer calls at higher risk of call overlap/signal masking. If overlaps occur less than expected by chance, other possible explanations are auditory suppression of repeated calls by responsive calls (e.g. Larter & Ryan 2024; Norton et al 2022) or the general self-suppression of repeat calls, which could indeed be indicative of an expectation of a vocal response or the result of differential usage of repeated calls across contexts. With the current dataset, the authors could at least compare the relative frequencies of repeated calls (short component) of subject individuals in the F2F vs Pre & Post phases.

3) In each experimental pairing, the subject individual was given a 15 minute acclimation period (PRE phase), whereas the facing bird was introduced immediately prior to the test. Relocating birds has been shown to affect vocalization rates (Zai et al 2025). Did transporting birds have effects on call rates? Specifically, were there any asymmetries in calling behavior when birds were in the subject vs. facing role/more vs. less acclimated?

Additional Minor Comments:

Lines 40-41, 46-47: There is evidence that the inter-speaker intervals during conversational turn-taking can be influenced by linguistic information/the speech planning network (e.g. Castellucci et al 2022).

Line 257: AIC should be defined as Akaike Information Criterion at first use.

Line 353: “Monotonic” rather than “Monotonous”.

Lines 382-383: It is not clear how the absence of “temporal regularity of vocal exchanges” has been determined. The authors previously defined temporal regularity as “stable time interval between vocalizations of two individuals and significant avoidance of vocal overlap” (lines 54-55). Is the “short component” distribution of exchange transitions not stable? Also, as mentioned above, the occurrence of overlaps is reported to be very low, but not assessed in terms of its significance. Greater consistency in the use of terms would be helpful here.

Line 401: “Why *do Java sparrows call contagiously?”

References:

Beckers, G. J., & Gahr, M. (2010). Neural processing of short-term recurrence in songbird vocal communication. PLoS One, 5(6), e11129.

Stowell, D., Gill, L., & Clayton, D. (2016). Detailed temporal structure of communication networks in groups of songbirds. Journal of the Royal Society Interface, 13(119), 20160296.

Larter L. C. and Ryan M. J. (2024) Sensory-motor tuning allows generic features of conspecific acoustic scenes to guide rapid, adaptive, call-timing responses in túngara frogs Proc. R. Soc. B.29120240992

P. Norton, J.I. Benichov, M. Pexirra, S. Schreiber, & D. Vallentin, (2022) A feedforward inhibitory premotor circuit for auditory–vocal interactions in zebra finches, Proc. Natl. Acad. Sci. U.S.A. 119 (23) e2118448119.

Zai A.T., Rodrigues D.I., Stepien A.E., Lorenz C., Giret N., Adam I., et al. (2025) Familiarity of an environment prevents song suppression in isolated zebra finches. PLoS ONE 20(1): e0307126.

Castellucci, G.A., Kovach, C.K., Howard, M.A. et al. (2022). A speech planning network for interactive language use. Nature. 602, 117–122

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Reviewer #1: No

Reviewer #2: No

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PONE-D-24-46388R1Temporal regularities of vocal exchange in Java sparrowsPLOS ONE

Dear Dr. Koda,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. I apologize for the long turn-around time for your revised manuscript. I felt it was important to get comments from both of the original reviewers and might take longer if new reviewers were engaged. Both Reviewers feel the paper has been significantly improved. However, there are some further concerns. Please respond to all the specific comments, especially those of Reviewer #1. Please submit your revised manuscript by Jul 12 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

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We look forward to receiving your revised manuscript.

Kind regards,

David S Vicario, Ph.D.

Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1:  The manuscript by Kikuchi et al is greatly improved following reviewer feedback. I appreciate the time the authors spent revising the manuscript to make the methodology and results clearer and the data interpretation more focused.

The generalization between birds and mammals, both of which are large and varied taxonomic groups, has been mostly eliminated. Ideally, the lingering references to the larger groups (e.g. line 25: “This contrasts with the temporal characteristics of vocal exchanges observed in mammals”), should be focused further to not suggest that the scientific community is certain that all mammals (or birds) share this trait – this is not something we can/cannot know. While the introduction does a fine job of providing more nuanced explanations of that sentence in particular, refraining from overgeneralizing should be avoided.

There is an additional analysis that may add to the help clarify why no differences were observed between tr and te transitions. Do tr intervals change based on social context? In other words, are the tr intervals longer or shorter when the bird has no partner bird to exchange calls with? Comparing the tr interval across the 3 phases of the experiment (PRE, F2F, POST) may provide useful insight into the utility of that transition based on whether the bird is alone or not. If it is the same across all three contexts, it might indicate that the birds are not using a call to communicate with a partner birds. However, if the tr is longer in the F2F phase compared to the other two that could suggest that they are awaiting a potential response. Similarly, if the POST tr interval is different from PRE or F2F, that might also suggest the role of the call in an attempt to contact conspecifics.

This suggested analysis (or something similar) might also help address the gap that the authors identify on lines 92-95 (“…while studies on the intervals between repeated transitions remain limited”). The current manuscript, as written, focuses more on the differences (or lack thereof) between repeated and exchanged transitions. An analysis focused solely on the repeated transitions would better address this gap.

To further strengthen the argument presented in the introduction, I encourage the authors to revisit the paragraphs on pages 5-6 (lines 96-121). I wonder if swapping the order of those two paragraphs might be helpful, particularly because lines 116-117 (“Specifically, mammals are more likely to expect and anticipate responses, whereas birds may not share the same expectations”) beg a “why?” even though it has been addressed to some extent in the previous paragraph. (Also, moving this sentence might be helpful to contextualize which birds and mammals have been studied to avoid the overgeneralization to all birds and/or mammals.

Given that I had difficulty interpreting Table 1/Figure 3 initially, the inclusion of the antilogarithmic values is extremely helpful. Please include the x-axis legend on Figure 3, specifying that you are plotting the antilogarithmic values. Additionally, I wonder if reorganizing Table 1 might be helpful by having the columns reflect the short and long components with the mean ± variance in the cells. Then you could more easily present the log transformed and anti-log values for each component.

Overall, modifications to the manuscript have helped showcase how calling behavior in java sparrows differs from those of other birds/mammals to better explain the utility of contagious calling and the value of comparative studies to evaluate how and why different groups of animals generate and modify vocal turn-taking.

Minor suggestions/observations:

1) Line 53, clarify ‘it’

2) Line 111-112, embed/modify the ‘birds fly much faster than mammals’ – there aren’t many mammalian species that fly, so referring to their movement as ‘travel’ may be more appropriate.

3) Consider combining the sentences on lines 125-127 for readability.

4) Line 178 – replace ‘enhance’ with ‘promote’ or something similar

5) Line 179 – replace ‘incubated’ – “The duration of the F2F phase was 15 minutes.”

6) Line 181-2: replace with “During the POST phase, facing individuals were removed from the soundproof room…”

7) Line 390 – use of the phrase, “affected by the vocal behavior of other individuals” doesn’t seem appropriate given that if you’d found differences between the transitions you would have been able to write this exact phrase. Consider clarifying.

8) Line 402 – modify to “To more appropriately test our hypothesis we will need to investigate vocal exchange …”

Reviewer #2:  The authors have sufficiently addressed my previous comments and the revised manuscript is considerably improved.

I would just like to point out the following minor phrasing issues, which can be easily edited prior to publication:

Lines 368-369: “Instead, they called in synchrony…” can be too easily misinterpreted as “called simultaneously”, which they apparently do not do in this paradigm, given the low instances of overlap. This new sentence can be removed.

Lines 402-404 “To test our hypothesis, we had to investigate the vocal exchanges and behavioral synchronization among more than three individuals in more natural, flock-like settings.”

- This was not done here. Perhaps authors meant “we would have to investigate…”.

-Also “our hypothesis” is a bit confusing here, given that the previous sentence refers to “our study”. Text should specify “To test our hypothesis regarding the synchronization of flocks, we would have to investigate…” (or similar).

Lines 414-415: It is not clear to me that the ability to avoid overlapping with a specific partner or in a playback experiment would necessarily mean that call overlaps would not increase in the presence of more callers. This new sentence can be removed.

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Reviewer #1: No

Reviewer #2: No

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Temporal regularities of vocal exchange in Java sparrows

PONE-D-24-46388R2

Dear Dr. Koda,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements. Thank you for submitting this interesting paper and for your thorough response to the Reviewers' suggestions. I apologize for the various delays in the editorial process. I look forward to seeing the article published so that others may read it.

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