PONE-D-25-07789Comparing migration of Whinchats Saxicola rubetra from Liberia and Nigeria: behaviours modified by differences in geography but unlikely to be constrained by themPLOS ONE

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Reviewers' comments:

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Comments to the Author

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Reviewer #1: Yes

Reviewer #2: Partly

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

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: No

Reviewer #2: No

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Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

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Reviewer #1: Review – Plos One

Comparing migration of Whinchats Saxicola rubetra from Liberia and Nigeria: behaviours modified by differences in geography but unlikely to be constrained by them

In this article, the authors describe the migration strategies of Whinchat, tagging birds from two non-breeding sites, allowing an unprecedented comparison with an impressive sample size for such a small migrant. This article provides valuable insight into the migration of this species, but also very important data that can apply to the Afro-palearctic migratory system in general, provided that more research will be carried out using a similar design. This work is worth publishing in Plos One and will be of interest for the specialized readership as well as for readers interested in more general novelty in biological research.

I listed minor suggestions hereafter. The only major remark concerns the visual classification method (see under methods), and hereby the limitations of the light-level geolocation to classify migration legs. This should be better explained in the methods, including more precisions on the general uncertainties, and some caution should be taken while presenting migration leg speed for example.

Title: I would suggest rephrasing the title in a shorter, simpler and clearer way (the second part takes time to associate to its meaning, at least for me). Mention could be made in the title that the study is based on non-breeding sites, because the “from” could be misleading for the non-specialized readership and because this is what makes this study more interesting.

Abstract

L. 19: “whinchats” plural?

L. 19: rephrasing suggestion: “a declining palearctic-breeding passerine” for example.

L. 21: not clear what is meant with differences in migratory connectivity between the two sites (connectivity is the fact that two non-breeding populations would go to two distinct breeding areas?) maybe reframe and put the connectivity argument into one separate sentence?

L. 23: “distance, duration…” (not necessary to mention speed, as it is here derived from distance and duration, no data on real speed in the air is shown).

L. 24 not clear from the sentence in the abstract why these two populations should have a different number of stopover sites (and not sure this is important for the abstract).

L. 28: “significant loop migration” : to avoid confusion, I suggest omitting this unnecessary “significant” unless related so statistical analyses here

L. 35: “able to adapt to potential climate change across Europe and West Africa”: this conclusion is not well supported by the data; I would be more cautious with mentioning this like that here.

Introduction

L. 41: probably true. However, most of these birds eat insects and this should be mentioned as a potential cause of decline, if the topic of the cause of decline is approached (not necessarily the core topic of this paper). Furthermore, declining long-distance migrants that eat seeds are persecuted (ortolan, turtle doves) and also decline. So there is a broad spectrum of reasons why these birds decline (with some exceptions locally), but discussing this here might not be needed.

L. 46: “to such changes in the non-breeding area “?

L. 49: I disagree with this expectation as it is phrased (many species have different migration strategies across populations, see blackcap for example), but this might be related to the phrasing.

Methods:

L. 205-209: I have some doubts about the accuracy of visual inspection method, as whinchats migrate on a mostly north-south axis and at times close to equinox (especially for the post-breeding migration). Could you provide some more details and quantify uncertainties, even broadly? Are there situations where migration periods could not be assessed accurately? I would be surprised if not.

L. 289: it is likely that there were stopovers of less than two days, but they were not detected with the classification method. Stopovers of one day are very common in other species while crossing the desert and the Mediterranean (see for example https://doi.org/10.1186/s40462-023-00381-6, which refers to a closely related species that performs such stops of less than a day, for example). I expect such short stops to occur in Whinchats at least partly: could you give more details about this?

L.298-299: I might have missed it, but did you set a time threshold to consider a non-breeding site? There are often stop over sites located close to non-breeding sites, but with only a few days I would not consider them as alternative non-breeding sites but rather stopover sites within the non-breeding region.

Results:

L. 353: did you have locations on the sea, and did you use a sea mask to correct for this?

L. 354: is the spatial precision sufficient to qualify the country in which the bird was, or should you stay with more general areas/directions?

“The subsequent flight for this bird crossed from the southern coast of Ghana to the

Mediterranean coast of Tunisia in a single leg of 3,538 km over a 5-day period”

If referring to more precise migration data in other species (https://doi.org/10.1186/s40462-023-00381-6 for example), it is likely that this bird landed over the day at least some hours and did not fly non-stop (in which case it would likely have taken max. 3 days), this could be explained better and discussed in the discussion section. It would be awesome to fit pressure loggers on Whinchats in the future to refine this (could be mentioned in the discussion).

L. 414: for discussion: could this be related to the onset of rains in Nigeria in the northern spring, from which Whinchats could benefit to refuel before crossing the desert (while rainfalls are less strongly seasonal in Liberia and start earlier?)

L. 447-453: I suggest skipping or being more cautious about the estimate of migration speed, as it is likely biased by the classification method and not a very important finding of the study.

L. 625: this partly solves my previous remark, but I would make it clearer in methods and results that the speed you measure is including some stationary phases. Since this migration leg speed is not a key finding of the study, I would give it less importance overall in the paper.

L. 685: I find this example of extremely short total migration time very interesting, could it be better highlighted in the results and maybe even in the abstract?

L. 694 – 695: probably not true for some desert stops?

Figures

On figure 3 especially, but also other figures, a visual representation of uncertainties could be valuable, especially for supposedly southwards movements before migration.

Thanks for this very interesting read.

Reviewer #2: In this study, authors clarified the characteristics of migration strategies of the whinchat, comparing them with two non-breeding populations. Authors focused on the 5 main topics of the two populations, i.e., 1) breeding ranges, 2) secondary non-breeding sites, 3) migration distance, the number of stopover sites and loop migration, 4) migration duration and phenology and 5) migration leg and stopover duration. The large dataset of whinchat’s migration presented some convincing results, but some problems should be corrected. My comments are listed below.

L130-131　

I think that there is insufficient evidence to provide a hypothesis that loop migration does not occur in Liberian wintering population. Please provide additional information regarding the reasoning behind your hypothesis.

L193

How did you treat the geolocator data during the equinox period? Tracked individuals appear to depart or arrive during the equinox period, as shown in Table S1. However, there is no description of the data analysis for this period.

L252-267

This paragraph should be moved to the result section.

L276

‘therefore do not include a random effect.’

Here, please add a sentence such as ‘i.e., analysed using Generalized Linear Models’.

L277, L433-441

Model selection and statistical tests should not be conducted simultaneously because their objectives are different. I think that model selection based on AIC/AICc is unnecessary because the focus, as in the other analyses, was on the significance of the explanatory variable (including the interaction term).

L377

‘-.0’: is this correct?

L358-360

I could not understand how the distance was calculated. Please explain it more precisely.

L440

I think that P=0.11 is not marginal.

L568　

Figure 2? I think Figure 1 is correct here.

L568

‘Our Liberia results possibly show this trend as well’ I think that it is over discussion here.

L633-634

Replace [ ] with ( ).

L1010

I think that the line colors of the minimum convex polygons are reversed between the Liberian and Nigerian populations in Figure 2.

L1034　

It seems that the table is misaligned. Is it correct?

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Reviewer #1: No

Reviewer #2: No

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Comparing migration of Whinchats Saxicola rubetra from the non-breeding grounds in Liberia and Nigeria: differences due to geography but otherwise very similar

PONE-D-25-07789R1

Dear Dr. Cresswell,

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.

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Academic Editor

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Additional Editor Comments (optional):

Thank you very much for the quick revision of the manuscript. Both reviewers and I found the revision to be mostly sufficient. Please refer to and incorporate the remaining minor feedback from Reviewer 2, and I think the manuscript is ready for publication.

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: All comments have been addressed

Reviewer #2: (No Response)

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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: No

Reviewer #2: No

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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: This version should be ready for publication. All points questioned in my previous review were addressed in the revised manuscript. In the few cases where the authors decided not to follow a suggestion, they justified their decision.

I agree with the author's response about sea mask bias.

Reviewer #2: I am approximately satisfied with your revision, but some problems are still present. Please check the comments below.

[L143] ‘Liberian and Nigerian whinchats will have similar:’ should be moved to next raw in hypothesis 5 as ‘5. Liberian and Nigerian whinchats will have similar: migration leg distance and ~~’

[L449] Add the “Liberian” and “Nigerian” at the top of the column for clarity of correspondence of the data and the non-breeding populations.

[L452] P , 0.0004 ->> P = 0.0004

[L542] I previously pointed out that "P = 0.11 is not marginal." You deleted the word "marginal" according to my suggestion, but it seemed to interpret the result as "significant". However, a P-value of 0.11 typically indicates non-significance. That said, the difference in mean migration leg distance between spring and autumn migrations of the Nigerian wintering population appears to be quite large (over 400 km), based on the values in Table 1. Please recheck accuracy of the results, i.e., mean values, standard errors, and t- and P-values (-488 km + 309SE, t = -1.5, P = 0.11), and revise the Results and Discussion sections (e.g., line 603, etc.) accordingly to reflect the accurate results.

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Reviewer #1: No

Reviewer #2: No

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