PONE-D-19-18222

Drone-based effective counting and ageing of hippopotamus (Hippopotamus amphibius) in the Okavango Delta in Botswana

PLOS ONE

Dear Ms Inman,

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.

The main issues relate to the statistical analyses. Reviewer #2 provides some very specific suggestions concerning the models that should be used given the data you have on hand. Please address this issue with an appropriate re-analysis. Reviewer #2 also suggests that the degrees of freedom should be adjusted for possible bias due to small sample sizes. This should also be addressed.

Finally, is the "true" number of hippos actually known? If so, this should be used to assess the relative performance of the drone and land-based survey methods. I would imagine that for such a species, this might actually be possible!

On a personal note, you were very fortunate that the animals were not very bothered by the drone even at 40m. In my experience with horses and deer, animals appear to be very sensitive to the articifial buzz of a multirotor UAV. I wonder if perhaps the hippo's ear is not so sensitive to these sound frequencies (as compared to a horse, for example). 

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PLOS ONE

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Reviewers' comments:

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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: Yes

Reviewer #2: Partly

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

Reviewer #1: Yes

Reviewer #2: No

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Reviewer #1: Yes

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: This is well executed research utilizing drone technology. As the technology develops to overcome the difficulties of drone control raised by authors in Discussion, this new techniques can be used widely in ecological monitoring.

Reviewer #2: My comments for the authors are contained in the attached document. The manuscript is fairly well written and easy to understand. The key weakness of the manuscript relates to the representation of the random variation in the data. As presented the models used do not adequately account for the potential total variation in the data.

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Reviewer #1: No

Reviewer #2: No

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Attachments

Attachment

Submitted filename: Review_Hippo surveys.docx

Drone-based effective counting and ageing of hippopotamus (Hippopotamus amphibius) in the Okavango Delta in Botswana

PONE-D-19-18222R1

Dear Dr. Inman,

We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements. Congratulations! 

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With kind regards,

Tim A. Mousseau

Academic Editor

PLOS ONE