Two common European songbirds elicit different community responses with their mobbing calls
based on reviews by 2 anonymous reviewers
Acoustic cues and season affect mobbing responses in a bird community
Abstract
Recommendation: posted 27 February 2023, validated 28 February 2023
Parker, T. (2023) Two common European songbirds elicit different community responses with their mobbing calls. Peer Community in Ecology, 100420. https://doi.org/10.24072/pci.ecology.100420
Recommendation
Many bird species participate in mobbing in which individuals approach a predator while producing conspicuous vocalizations (Magrath et al. 2014). Mobbing is interesting to behavioral ecologists because of the complex array of costs of benefits. Costs range from the obvious risk of approaching a predator while drawing that predator’s attention to the more mundane opportunity costs of taking time away from other activities, such as foraging. Benefits may involve driving the predator to leave, teaching relatives to recognize predators, signaling quality to conspecifics, or others. An added layer of complexity in this system comes from the inter-specific interactions that often occur among different mobbing species (Magrath et al. 2014).
This study by Salis et al. (2023) explored the responses of a local bird community to mobbing calls produced by individuals of two common mobbing species in European forests, coal tits, and crested tits. Not only did they compare responses to these two different species, they assessed the impact of the number of mobbing individuals on the stimulus recordings, and they did so at two very different times of the year with different social contexts for the birds involved, winter (non-breeding) and spring (breeding). The experiment was well-designed and highly powered, and the authors tested and confirmed an important assumption of their design, and thus the results are convincing. It is clear that members of the local bird community responded differently to the two different species, and this result raises interesting questions about why these species differed in their tendency to attract additional mobbers. For instance, are species that recruit more co-mobbers more effective at recruiting because they are more reliable in their mobbing behavior (Magrath et al. 2014), more likely to reciprocate (Krams and Krama, 2002), or for some other reason? Hopefully this system, now of proven utility thanks to the current study, will be useful for following up on hypotheses such as these. Other convincing results, such as the higher rate of mobbing response in winter than in spring, also merit following up with further work.
Finally, their observation that playback of vocalizations of multiple individuals often elicited a more mobbing response that the playback of vocalizations of a single individual are interesting and consistent with other recent work indicating that groups of mobbers recruit more additional mobbers than do single mobbers (Dutour et al. 2021). However, as acknowledged in the manuscript, the design of the current study did not allow a distinction between the effect of multiple individuals signaling versus an effect of a stronger stimulus. Thus, this last result leaves the question of the effect of mobbing group size in these species open to further study.
REFERENCES
Dutour M, Kalb N, Salis A, Randler C (2021) Number of callers may affect the response to conspecific mobbing calls in great tits (Parus major). Behavioral Ecology and Sociobiology, 75, 29. https://doi.org/10.1007/s00265-021-02969-7
Krams I, Krama T (2002) Interspecific reciprocity explains mobbing behaviour of the breeding chaffinches, Fringilla coelebs. Proceedings of the Royal Society of London. Series B: Biological Sciences, 269, 2345–2350. https://doi.org/10.1098/rspb.2002.2155
Magrath RD, Haff TM, Fallow PM, Radford AN (2015) Eavesdropping on heterospecific alarm calls: from mechanisms to consequences. Biological Reviews, 90, 560–586. https://doi.org/10.1111/brv.12122
Salis A, Lena JP, Lengagne T (2023) Acoustic cues and season affect mobbing responses in a bird community. bioRxiv, 2022.05.05.490715, ver. 5 peer-reviewed and recommended by Peer Community in Ecology. https://doi.org/10.1101/2022.05.05.490715
The recommender in charge of the evaluation of the article and the reviewers declared that they have no conflict of interest (as defined in the code of conduct of PCI) with the authors or with the content of the article. The authors declared that they comply with the PCI rule of having no financial conflicts of interest in relation to the content of the article.
This work was supported by the French Ministry of Research and Higher Education funding (to A.S. PhD grants 2019-2022)
Evaluation round #4
DOI or URL of the preprint: https://www.biorxiv.org/content/10.1101/2022.05.05.490715v4
Version of the preprint: 4
Author's Reply, 27 Feb 2023
Dear recommender,
Please find the manuscript with a formatting helping scientific readers. We changed the word '15' to 'fifteen'. Thank you again for all the advice given to improve this manuscript.
Decision by Tim Parker, posted 21 Feb 2023, validated 23 Feb 2023
Dear Ambre Salis,
Thank you for your revisions. As soon as you post your re-submission, I will recommend this preprint.
I have one small editorial request - on line 282, please change “15” to “Fifteen” because it is the start of a sentence.
Sincerely,
Tim Parker
Evaluation round #3
DOI or URL of the preprint: https://doi.org/10.1101/2022.05.05.490715
Version of the preprint: 3
Author's Reply, 21 Feb 2023
Decision by Tim Parker, posted 07 Feb 2023, validated 09 Feb 2023
Dear Ambre Salis,
Thank you for your revision. I am prepared to recommend this pre-print after you make a few small edits to improve clarity.
I look forward to seeing the final manuscript.
My suggestions follow by line number:
103: “playbacks” should be “playback”
also, “is” should be “in”
113: insert “)” after “hops”
250: This statement “The two main species, apart from coal and crested tits, were…” is, to me, misleading, since it suggests that both coal and crested tits responded more often than goldcrests, but from fig 1A, it seems that only crested tits were more common responders than goldcrests.
251: Here and elsewhere, I encourage consistency with bird name capitalizations. Given that you do not capitalize coal tit or crested tit, I suggest you not capitalize goldcrest, marsh tit, or others.
283: could you state the rates of occurrence at playback of coal tits and crested tits relative to goldcrests and chaffinches.
Also, I am confused – given the number of crested tits responding was higher than the number of goldcrests (according to Fig 1B), how is it that goldcrests responded 24% of the time and fewer than 25% of trials had any response? This suggests that goldcrests responded in (almost) every case where there was any response from any species – is that correct? Also, does this mean that most of the trials with crested tits responding had multiple individuals responding, and so the percent of trials with crested tits responding was not higher than the percent of trials with goldcrests, even though the total number of trials with goldcrests responding was higher than (or as high as) the number with crested tits?
319: change “per treatment” to “across treatments”
334: change to “middle graphs are responses”
380: change “modulates” to “modulate”
Also, I don’t think we have sampled widely enough across birds to say “usually” here. Maybe say “often”. Or maybe say something like “Where it has been studies, birds usually …”
427: insert “a” before “’community’”
443: change “explore” to “explored”
483: insert “support for” so that this reads “we found support for different models”
Sincerely,
Tim Parker
Evaluation round #2
DOI or URL of the preprint: https://doi.org/10.1101/2022.05.05.490715
Version of the preprint: 2
Author's Reply, 05 Feb 2023
Decision by Tim Parker, posted 05 Dec 2022, validated 05 Dec 2022
Reviewed by anonymous reviewer 2, 21 Nov 2022
I thank the authors; they have done great work addressing all the concerns and queries I raised in the first round. The statistical method used in conjunction with the experimental design (factorial design) is now appropriate. The preprint organisation has also been improved to a level the reader could easily follow.
I have made a couple of suggestions to improve the presentation of results and have a query of the models in Table 1. Otherwise, the preprint is scientifically sound and may require editing before publishing in PCI or any other journal.
Major comments:
In Table 1, mobbing responses are listed under two different response variables: response occurrence and intensity. As far as I understood, and what I see from model syntax in the R script, the zi- zero inflation part reported under the mobbing intensity.
In fact, the zi part of the model helps to define what variables contribute to zero inflation; it could be one variable than the other, or both variables equally contribute to zeros inflation. As the authors mentioned, there is no distinction between true and false zeros in Hurdle models. However, for example, the authors need to justify why they think that, Emitter species + number of callers contribute to zero inflation in one model and, why only the Emitter species contribute to zero inflation in another model (this is an example, it may apply to all the models presented in the table).
In addition, authors may consider defining theta in the table caption or the statistical methods section where appropriate; otherwise, people who think in a Bayesian way might be confused with parameter estimates.
There are a couple of issues that need to be resolved or need explanation here:
01. I agree that the presence of excess zeros does not warrant using zero inflation models. Hurdle models can use alternatively, but clarification is needed on how the zero (inflation) arises in three different analyses. The first step is to evaluate the overdispersion (either with Poisson or Negative binomial distribution), which may be done using a simulation test. If the authors did overdispersion tests before selecting the Hurdle model procedure, please mention it on Page 9, lines 185-188.
02. In this study, as far as I understood, zeros (inflation) may arise on two processes: 1 zero may occur when the species do not present at the point or species present at the point but did not show any mobbing responses. For example, in community-level analyses, the number of responding birds may represent single species or different species (i.e., if four birds showed a mobbing response, it could be from a single species or four different species).
Were zero responses specifically generated, either absence of the mobbing species or no mobbing response towards the soundtracks, particularly for coal tits and crested tits? Clear identification of the zero-generation process is also essential when defining the glmmTMB models.
03. Using the same terms in both factorial design and the models makes sense. Model selection may help choose different distribution fittings (i.e., negative binomial vs Poisson) while keeping the fixed effects in the model. This could also extend to test the hypothesis of the additive vs interaction effect of the same model instead of dropping or adding terms.
04. Why is glmmTMB control “BFGS” used in models? I presume this is because to account lack of convergence in some models. If that is the case, please include the relevant details which would be helpful for the reader in the statistical methods section.
Zuur,A.F and Ieno,E.. Beginner’s Guide to Zero-Inflated Models with R. 2016. (Chapter 6 for Hurdle models). This book extensively discusses the statistical and practical background and updated version of the methods introduced in Zurr et al. 2009, which authors cited.
Minor comments:
Page 4, line 86: rephrase or add (unclear)
Page 4, line 88: If the authors can back this with a reference, that would be great.
Page 5, line 110: what is ‘X’
Page 6, line 112: please give the breakdown (n=22, coal tits? great tits?).
Page 9, line 179: R version 3.6.1 was released in 2019, not 2022. Please ensure all the package versions used in the preprint are correct and include their references.
Page 9, lines 195-197: Is the overdispersion the main reason to use negative binomial distribution??
Page 10, line 208: if it is due to sampling size, then AIC corrected is also helpful; perhaps it may be unobserved heterogeneity. Brewer et al. 2016 Methods. Ecol.Evol. Volume 7(6) p.679-692.
Page 10, line 200: were random effects introduced as an intercept?
Page 11, line 225: it would be helpful to provide contrast measures using the final model. The authors may use the emmeans package (Ver 1.8.2), 2022 or an equivalent package to get contrast estimates. Estimates also provide strong statistical evidence for the graphical presentations in Fig1-3.
I am sure the following reference: Ratnayake et al. 2021. Behav.Ecol Vol 32(5) pages 941-951. It may be helpful to include some necessary information in the methods section, and please note that this is not an indication to cite the reference. However, the reference may be relevant as the study used mobbing calls of noisy minors to test the occurrence and the intensity of the responses of Australian magpies.
I hope comments will help improve the preprint quality, particularly parts in the statistical methods section. Finally, I congratulate the authors for their good work.
Evaluation round #1
DOI or URL of the preprint: https://doi.org/10.1101/2022.05.05.490715
Version of the preprint: 1
Author's Reply, 04 Nov 2022
Decision by Tim Parker, posted 03 Aug 2022
Dear Ambre Salis,
I apologize for the delay in providing these comments. By the time I received the second review, I had left on holiday for much of July.
Two independent reviewers and I have read your manuscript (Acoustic cues and season affect mobbing responses in a bird community). The reviewers and I all see value in this study. I appreciate the use of a thorough design to simultaneously evaluation multiple potential influences on the response to mobbing calls, the large sample of trials, and the evaluation of an important assumption of your experiment. However, we also all identified some important areas where improvements are merited. I have provided some detailed comments below and both reviewers provided detailed suggestions as well. Please carefully consider all these suggestions and either implement the suggestions or explain why you have not done so if you chose to resubmit a revised manuscript.
Before providing my detailed comments and those of the reviewers, I want to call attention to several points that are particularly important.
Both reviewers noted that group size may not be expected to correlate with the reliability of mobbing calls. I encourage you to explore the literature on this subject further, and to update your discussion of this topic.
Reviewer 1 and I both felt that your explanation in the main text of the supplementary experiment (done to assess the likelihood of overlapping responses between playback locations) is insufficient. I encourage you to either bring this experiment to the main document, or at least to provide more details in the main document.
Reviewer 1 and I also wanted to see more information about the 3-bird playback stimuli. Besides addressing the questions of Reviewer 1, I encourage to consider adding the stimuli and the sound spectrograms of the stimuli to your supplement.
On a related topic, both reviewers and I share the concern about your interpretation of the 3-bird stimulus due differences in duty cycle between the treatments.
Reviewer 2 identified several important issues related to your statistical analyses, including a model convergence error (which I also replicated when I ran your code). I do not believe there is only a single correct way to analyze a dataset, but I would like you to seriously consider Reviewer 2’s recommendations and concerns.
Sincerely,
Tim Parker
What follows are some specific concerns that I noted as I read the manuscript (organized by line number):
41: “We therefore confirm the hypothesis” – should be something like “We therefore find support for the hypothesis”
161-162: when a bird was detected in the area, what was your protocol? Did you wait for it to leave or move to another location?
113: How did you determine the order in which you visited survey locations?
159: How did you resolve differences in observations between observers?
174: please explicitly state that you excluded cases of zero detections from the intensity analyses
177: which versions of the lme4 R package? Also, please cite the package (e.g., ‘Bates et al….’ for lme4).
179: if you decide to remain with analyses using Poisson error (instead of taking the suggestions of reviewer 2), you should report the details of your test for overdispersion.
183-185: This sort of step-wise procedure can lead to biased model estimates (see Forstmeier and Schielzeth. 2011. Behav Ecol Sociobiol 65:47–55). Given that you present full models, it is not clear to me why you were using a step-wise procedure.
189: again, more information needed about packages
Table 1 vs. Table 2. The first table in the text is labeled ‘Table 2’, but presumably it should be labeled ‘Table 1’ – it seems that when you cite Table 1 in the text, you are referring to the table currently labeled ‘Table 2’
Table 2 (as currently labeled): Why do you not present number of mobbers results for coal and crested tits? You seem to have that information in another form in Figure 2.
Table 1 (as currently labeled): The heading says “propensity and intensity”, but the content of the table looks like only one or the other, but definitely not both.
Table 1 and Table 2/ Figure 2: You currently only present the estimates in graphical form. It would be useful to present the actual numbers (either in an expanded form of Tables 1 and 2, or maybe in a table in the supplement).
Table 2: ‘NB’ should be defined in the heading
338: You should more explicitly acknowledge the limitations of your experiment here (duty cycle not standardized).
Reviewed by anonymous reviewer 1, 23 May 2022
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