An experimental approach to evaluate the potential of drones in terrestrial mammal research: a gregarious ungulate as a study model

Research on the use of unmanned aircraft systems (UAS) in wildlife has made remarkable progress recently. Few studies to date have experimentally evaluated the effect of UAS on animals and have usually focused primarily on aquatic fauna. In terrestrial open arid ecosystems, with relatively good visibility to detect animals but little environmental noise, there should be a trade-off between flying the UAS at high height above ground level (AGL) to limit the disturbance of animals and flying low enough to maintain count precision. In addition, body size or social aggregation of species can also affect the ability to detect animals from the air and their response to the UAS approach. To address this gap, we used a gregarious ungulate, the guanaco (Lama guanicoe), as a study model. Based on three types of experimental flights, we demonstrated that (i) the likelihood of miscounting guanacos in images increases with UAS height, but only for offspring and (ii) higher height AGL and lower UAS speed reduce disturbance, except for large groups, which always reacted. Our results call into question mostly indirect and observational previous evidence that terrestrial mammals are more tolerant to UAS than other species and highlight the need for experimental and species-specific studies before using UAS methods.

The authors have missed a significant amount of literature on this subject. The statement in the abstract that progress so far has "mainly been derived from aquatic fauna studies" is perhaps not accurate given the wealth of other studies on terrestrial animals, such as those listed at the end of my review.
Throughout the paper the authors make incorrect use of the word "altitude". Altitude has a specific meaning, which is the height above sea level. To say you flew the drone at 60m altitude at the co-ordinates specified would likely mean you were flying underground. All instances of the word altitude should be replaced with "height" or "height AGL". I know this might not sound very scientific but it is the correct term.
Clarity of method description needs to be improved throughout. More detail is required in table 1, each flight type needs split into heights and number of photos gathered. If no photos were taken on a flight -ie it was for behaviour observation only, this should also be indicated. It is not clear if behaviour observing flights were performed before, after or at the same time as photo gathering flights. It may be that the animals became more habituated to the drone in later flights so this needs to be made clearer. The specific speeds need to be clarified for the scanning flights rather than just the range. What was the overlap in photos taken on the horizontal flights?
For the behaviour observations, how were the observations made and by how many people?
Its not clear if one of the aims of the study was to count the total number of guanacos, or if you were only interested in the number per photo. If the total number was a value of interest this should also be indicated along with details of how you account for animals moving between photos in scanning flights.
The authors mention "accuracy" in the discussion. Since no "true" ground counts were made, or at least weren't reported if they were made, it is hard to make strong statements about accuracy. The variance between different observer's counts is what is reported, and this should be made clear. Its true that variation will be related to accuracy if taking averages, but since the authors don't know if there may be a systematic offset between true and observed counts, strong statements about accuracy should be removed.

Introduction
As mentioned, most research today has been done on marine mammals and birds, however, I think more could be included here about previous research into disturbance of UAS on different species, particularly that terrestrial mammals. For example Bennitt et al. 2019, Terrestrial mammalian wildlife responses to Unmanned Aerial Systems approaches, who found varying degrees of response several terrestrial mammal species to UAS. Can you highlight the necessary advance brought by this study in contrast to previous work? Also, research such as this that are mentioned in conclusion could be raised earlier in introduction describing that studies to date suggest terrestrial mammals may respond less ( Mulero-Pázmány M, Jenni-Eiermann S, Strebel N, Sattler T, Negro JJ, Tablado Z (2017) Unmanned aircraft systems as a new source of disturbance for wildlife: A systematic review. PLoS ONE 12(6): e0178448). L48 in comparison to what? i.e. UAS are relatively less noisy than manned aircraft but not remote sensing L51 I'm not sure I understand what is meant here, can you clarify? Perhaps that recording images using UAS offers an advantage over traditional ground surveys because the images are permanent and can be re-visited in the future for other, unforeseen analyses? L58-59 Needs clarification and fixing for english L61 "is" instead of "are" Methods L82 could you describe a bit more the enclosure particularly with relevance to their available space to react to the drones L94 Why only 2 pictures taken at Payunia? Or is this number of pictures at each elevation for VF flights? L104 how was group size counted? Here, and below in describing S flights, can you clarify how group size and behaviour was recorded? i.e. were there observers on foot, were the guanacos habituated to humans on the ground, or was this data collected using the imagery? If the latter, can you provide more detail as it sounds from L105 and 106 that images were only captured if the animals did not react. L114 can you also provide more detail on the behavioural data? i.e. data categories (forage, vigilance etc., is mentioned at the group level -was this scored based on the majority of the individuals in the group or quantified in some way i.e. number of individuals doing each behaviour on each behavioural scan? L134-139 as above, I think this needs some clarification on the unit of analysis (i.e. one measure of behaviour per group, or individuals?) L140 can you clarify if this is using imagery? L150 "with VC counts at 200 m found to be more variable compared to"

Discussion
Is it possible to highlight the importance and contribution of this study in contrast to Bennitt et al. 2019's recent analysis? Perhaps by paying more attention to inter-species differences and why reproducing these studies across a range of species and ecotypes is necessary. Given that responses may vary by species, could you also provide some discussion of the importance of these findings that may be specific to Guanacos or to disturbance potentially caused by the increasing recreational use of drones (if this is also occurring across S. America)? L202 perhaps "aid" would make more sense here than "collaborate"?

28-Sep-2019
Dear Dr Schroeder, The editors assigned to your paper ("An experimental approach to evaluate the potential of drones in terrestrial mammal research: a gregarious ungulate as a study model") have now received comments from reviewers. We would like you to revise your paper in accordance with the referee and Associate Editor suggestions which can be found below (not including confidential reports to the Editor). Please note this decision does not guarantee eventual acceptance.
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We suggest the following format: AB carried out the molecular lab work, participated in data analysis, carried out sequence alignments, participated in the design of the study and drafted the manuscript; CD carried out the statistical analyses; EF collected field data; GH conceived of the study, designed the study, coordinated the study and helped draft the manuscript. All authors gave final approval for publication.
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Once again, thank you for submitting your manuscript to Royal Society Open Science and I look forward to receiving your revision. If you have any questions at all, please do not hesitate to get in touch.
Kind regards, Andrew Dunn Royal Society Open Science Editorial Office Royal Society Open Science openscience@royalsociety.org on behalf of Dr Alecia Carter (Associate Editor) and Kevin Padian (Subject Editor) openscience@royalsociety.org Associate Editor's comments (Dr Alecia Carter): Dear authors, I have now received two reviews of your manuscript and read it myself. We are all in agreement that your study is timely and interesting and, in general, well-executed. However, I agree with the reviewers that the manuscript requires improvements. In particular, much greater clarity in the methods and results sections is required for this work to be understandable (and replicable). The reviewers also highlight a large literature on terrestrial applications of drones that has been missed in this submission. The feedback from both reviewers is very constructive and I anticipate that this manuscript will be greatly improved by carefully incorporating their comments in a resubmission. Thank you for submitting your manuscript to RSOS.

Comments to Author:
Reviewers' Comments to Author: Reviewer: 1 Comments to the Author(s) Review also attached as pdf This paper presents the results of several experiments to determine the reaction of guanaco to drones, and the variation of manual counts of these animals based on photos taken from the drone. Both of these tests were performed for a variety of drone heights and speeds of approach to the animals. The experimental design with regards to the drone operations themselves is ok, but the analysis needs more work to be of publishable quality. The methods and results section are somewhat unclear and lack necessary detail. It's true that there is not a lot of previous work in the reactions of animals to drones; and this reviewer agrees that it is likely species specific, and subject to many factors, and that we should be making note of animal reactions and adjusting observing strategies accordingly. Overall this paper does provide some new insight which may be of use to the community, provided some revisions are made.
The authors have missed a significant amount of literature on this subject. The statement in the abstract that progress so far has "mainly been derived from aquatic fauna studies" is perhaps not accurate given the wealth of other studies on terrestrial animals, such as those listed at the end of my review.
Throughout the paper the authors make incorrect use of the word "altitude". Altitude has a specific meaning, which is the height above sea level. To say you flew the drone at 60m altitude at the co-ordinates specified would likely mean you were flying underground. All instances of the word altitude should be replaced with "height" or "height AGL". I know this might not sound very scientific but it is the correct term.
Clarity of method description needs to be improved throughout. More detail is required in table 1, each flight type needs split into heights and number of photos gathered. If no photos were taken on a flight -ie it was for behaviour observation only, this should also be indicated. It is not clear if behaviour observing flights were performed before, after or at the same time as photo gathering flights. It may be that the animals became more habituated to the drone in later flights so this needs to be made clearer. The specific speeds need to be clarified for the scanning flights rather than just the range. What was the overlap in photos taken on the horizontal flights?
For the behaviour observations, how were the observations made and by how many people?
Its not clear if one of the aims of the study was to count the total number of guanacos, or if you were only interested in the number per photo. If the total number was a value of interest this should also be indicated along with details of how you account for animals moving between photos in scanning flights.
The authors mention "accuracy" in the discussion. Since no "true" ground counts were made, or at least weren't reported if they were made, it is hard to make strong statements about accuracy. The variance between different observer's counts is what is reported, and this should be made clear. Its true that variation will be related to accuracy if taking averages, but since the authors don't know if there may be a systematic offset between true and observed counts, strong statements about accuracy should be removed.
Were there any false positives identified? Given the variation in counts this seems likely. This and possible causes of false positives should be discussed.
Why was the response of the animals not monitored during VF flights? Some previous papers find that animals react strongly to a descending drone.
Was there a difference in behaviours between the wild and captive groups?
The first paragraph of the results section needs clarifying. It could read as though the count variation you are reporting is between images of the same group at different heights (I'm fairly sure that's not what you mean). Needs to be clear that the variation is between different observers counting from the same images.
Line 47 -Drones are a type of remote sensing platform, presumably you are referring to satellites here?
Line 54 -its not clear what you mean by "sampling coverage capacity" or "low flight autonomy". These terms need to be defined more clearly or replaced.
Lines 58-61 -I'm not convinced this is true as there are many papers on terrestrial animals as well.
Line 64 -a rainforest environment is very noisy, are you sure that marine environments are louder? Are there any measurements to support this statement? Line 111 -"y" -> 'and' Line 163 -Its not clear how 87% arises from 2 groups of about 50% each. Needs to be clearer where this number comes from.
Line 169 -Does this mean 14% more groups or 14% more animals?
Line 200 -similar to above, the variation has increased but you can't really make strong statements about the probability of miscounting in an absolute sense. Comments to the Author(s) This study expands on our understanding of how to best implement, and the disturbance caused by, the use of UAS to census and study terrestrial mammal species. Studies such as these that specifically measure and test the disturbance to animals through different flight patterns, noise levels, and altitudes are important given the burgeoning use of UAS in wildlife research. The study is well conducted and the manuscript well written. There are a few minor changes that could be made to clarify the English and I've listed these more specifically below, but overall the introduction could contextualize the proposed research in more detail compared to what has been done to date and provide more detail and clarification in the methods to improve the manuscript.

Introduction
As mentioned, most research today has been done on marine mammals and birds, however, I think more could be included here about previous research into disturbance of UAS on different species, particularly that terrestrial mammals. For example Bennitt et al. 2019, Terrestrial mammalian wildlife responses to Unmanned Aerial Systems approaches, who found varying degrees of response several terrestrial mammal species to UAS. Can you highlight the necessary advance brought by this study in contrast to previous work? Also, research such as this that are mentioned in conclusion could be raised earlier in introduction describing that studies to date suggest terrestrial mammals may respond less ( Mulero-Pázmány M, Jenni-Eiermann S, Strebel N, Sattler T, Negro JJ, Tablado Z (2017) Unmanned aircraft systems as a new source of disturbance for wildlife: A systematic review. PLoS ONE 12(6): e0178448). L48 in comparison to what? i.e. UAS are relatively less noisy than manned aircraft but not remote sensing L51 I'm not sure I understand what is meant here, can you clarify? Perhaps that recording images using UAS offers an advantage over traditional ground surveys because the images are permanent and can be re-visited in the future for other, unforeseen analyses? L58-59 Needs clarification and fixing for english L61 "is" instead of "are" Methods L82 could you describe a bit more the enclosure particularly with relevance to their available space to react to the drones L94 Why only 2 pictures taken at Payunia? Or is this number of pictures at each elevation for VF flights? L104 how was group size counted? Here, and below in describing S flights, can you clarify how group size and behaviour was recorded? i.e. were there observers on foot, were the guanacos habituated to humans on the ground, or was this data collected using the imagery? If the latter, can you provide more detail as it sounds from L105 and 106 that images were only captured if the animals did not react. L114 can you also provide more detail on the behavioural data? i.e. data categories (forage, vigilance etc., is mentioned at the group level -was this scored based on the majority of the individuals in the group or quantified in some way i.e. number of individuals doing each behaviour on each behavioural scan? L134-139 as above, I think this needs some clarification on the unit of analysis (i.e. one measure of behaviour per group, or individuals?) L140 can you clarify if this is using imagery? L150 "with VC counts at 200 m found to be more variable compared to"

Discussion
Is it possible to highlight the importance and contribution of this study in contrast to Bennitt et al. 2019's recent analysis? Perhaps by paying more attention to inter-species differences and why reproducing these studies across a range of species and ecotypes is necessary. Given that responses may vary by species, could you also provide some discussion of the importance of these findings that may be specific to Guanacos or to disturbance potentially caused by the increasing recreational use of drones (if this is also occurring across S. America)? L202 perhaps "aid" would make more sense here than "collaborate"?

Author's Response to Decision Letter for (RSOS-191482.R0)
See Appendix A.

Comments to the Author(s)
The paper is much improved and generally scientifically sound for publication. There are only a few minor points I would like to see addressed.
Lines 53-54: "outweighed by several limitations" This is a pretty strong statement, and in fact the advantages of drones over foot surveys are already quite distinct even if some work does still need to be done. Please soften this.
Line 54: "low sampling area coverage" Relative to a foot survey even a 20-30 min drone survey can cover a much larger area, so this statement doesn't seem right.
Line 56: "time consuming data processing" Its true that processing lots of drone data by eye or by hand can be very time consuming, however is this time spent more than would be spent on a very long ground survey to make the same animal counts? The statement could perhaps be quantified better.
Line 66: "approximation" is the wrong word to use here. "Proximity" maybe?
Line 299: "results question previous mostly indirect and observational evidence" This is too strong a statement as you have only examined one species of animal. Its an important new observation but in context with the rest of the literature I think more evidence is needed to make a statement that strong.

Comments to the Author(s)
The changes made to the manuscript have better contextualized this research with what has been done to date and improved the clarity of the objectives and methods used. I have included just a few more comments below mostly regarding clarity and English. L23 this sounds as though the studies themselves are a concern -perhaps better to just say "Few studies to date have experimentally evaluated the effect of UAS approach on animals and have usually focused primarily on aquatic fauna" L29 "limit disturbance of animals and flying low enough to maintain count precision…" L58 "Moreover, images provide a permanent recording of data that can be re-visited and analysed again in the future, unforeseen research questions." L67 different types L70 "However, few studies have experimentally… animals, whilst those studies done to date have focused primarily…" L78 Include the authors names here and put the citation at the end of the relevant text., same for 22 and 23 L99 whilst maintaining count precision L134 english needs amending, perhaps "We approached the drone at 200 AGL until it was positioned directly above a previously selected group of guanacos. Then the drone was slowly lowered and pictures were taken at…" L139 approached the drone towards it L149 To be absolutely clear state whether group size was recorded by the observer here. L189-194 Were these behaviours recorded as counts of individuals doing each behaviour, as the predominant behaviour displayed by most of the group, or by focal individuals by the observer? L210 were not was -perhaps clearer to say "At 100 and 150m AGL only a small number of photos were captured that contained offspring, so we could not include these images in the analysis. L229 14% more groups reacted when the UAS was flown at 8-10m/s. L277 has been shown to L287 "which supports previous research suggesting other terrestrial mammals (which ones?) also react more to auditory disturbance" L298 spelling usually L318 include author names and move citation to end of text if structuring sentences this way L324 highlights L328 especially not specially L329-331 This sentence is very unclear, can you check and rephrase?  On behalf of the Editors, I am pleased to inform you that your Manuscript RSOS-191482.R1 entitled "An experimental approach to evaluate the potential of drones in terrestrial mammal research: a gregarious ungulate as a study model" has been accepted for publication in Royal Society Open Science subject to minor revision in accordance with the referee suggestions. Please find the referees' comments at the end of this email.
The reviewers and Subject Editor have recommended publication, but also suggest some minor revisions to your manuscript. Therefore, I invite you to respond to the comments and revise your manuscript.
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• Data accessibility It is a condition of publication that all supporting data are made available either as supplementary information or preferably in a suitable permanent repository. The data accessibility section should state where the article's supporting data can be accessed. This section should also include details, where possible of where to access other relevant research materials such as statistical tools, protocols, software etc can be accessed. If the data has been deposited in an external repository this section should list the database, accession number and link to the DOI for all data from the article that has been made publicly available. Data sets that have been deposited in an external repository and have a DOI should also be appropriately cited in the manuscript and included in the reference list.
If you wish to submit your supporting data or code to Dryad (http://datadryad.org/), or modify your current submission to dryad, please use the following link: http://datadryad.org/submit?journalID=RSOS&manu=RSOS-191482.R1 • Competing interests Please declare any financial or non-financial competing interests, or state that you have no competing interests.
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All contributors who do not meet all of these criteria should be included in the acknowledgements.
We suggest the following format: AB carried out the molecular lab work, participated in data analysis, carried out sequence alignments, participated in the design of the study and drafted the manuscript; CD carried out the statistical analyses; EF collected field data; GH conceived of the study, designed the study, coordinated the study and helped draft the manuscript. All authors gave final approval for publication.
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Once again, thank you for submitting your manuscript to Royal Society Open Science and I look forward to receiving your revision. If you have any questions at all, please do not hesitate to get in touch. The paper is much improved and generally scientifically sound for publication. There are only a few minor points I would like to see addressed.
Lines 53-54: "outweighed by several limitations" This is a pretty strong statement, and in fact the advantages of drones over foot surveys are already quite distinct even if some work does still need to be done. Please soften this.
Line 54: "low sampling area coverage" Relative to a foot survey even a 20-30 min drone survey can cover a much larger area, so this statement doesn't seem right.
Line 56: "time consuming data processing" Its true that processing lots of drone data by eye or by hand can be very time consuming, however is this time spent more than would be spent on a very long ground survey to make the same animal counts? The statement could perhaps be quantified better.
Line 66: "approximation" is the wrong word to use here. "Proximity" maybe?
Line 299: "results question previous mostly indirect and observational evidence" This is too strong a statement as you have only examined one species of animal. Its an important new observation but in context with the rest of the literature I think more evidence is needed to make a statement that strong.
Reviewer: 2 Comments to the Author(s) The changes made to the manuscript have better contextualized this research with what has been done to date and improved the clarity of the objectives and methods used. I have included just a few more comments below mostly regarding clarity and English.
L23 this sounds as though the studies themselves are a concern -perhaps better to just say "Few studies to date have experimentally evaluated the effect of UAS approach on animals and have usually focused primarily on aquatic fauna" L29 "limit disturbance of animals and flying low enough to maintain count precision…" L58 "Moreover, images provide a permanent recording of data that can be re-visited and analysed again in the future, unforeseen research questions." L67 different types L70 "However, few studies have experimentally… animals, whilst those studies done to date have focused primarily…" L78 Include the authors names here and put the citation at the end of the relevant text., same for 22 and 23 L99 whilst maintaining count precision L134 english needs amending, perhaps "We approached the drone at 200 AGL until it was positioned directly above a previously selected group of guanacos. Then the drone was slowly lowered and pictures were taken at…" L139 approached the drone towards it L149 To be absolutely clear state whether group size was recorded by the observer here. L189-194 Were these behaviours recorded as counts of individuals doing each behaviour, as the predominant behaviour displayed by most of the group, or by focal individuals by the observer? L210 were not was -perhaps clearer to say "At 100 and 150m AGL only a small number of photos were captured that contained offspring, so we could not include these images in the analysis. L229 14% more groups reacted when the UAS was flown at 8-10m/s. L277 has been shown to L287 "which supports previous research suggesting other terrestrial mammals (which ones?) also react more to auditory disturbance" L298 spelling usually L318 include author names and move citation to end of text if structuring sentences this way L324 highlights L328 especially not specially L329-331 This sentence is very unclear, can you check and rephrase?  It is a pleasure to accept your manuscript entitled "An experimental approach to evaluate the potential of drones in terrestrial mammal research: a gregarious ungulate as a study model" in its current form for publication in Royal Society Open Science.
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8-Oct-19
Response to Referees First of all, the authors would like to thank the Associate Editor and referees for their comments, which have contributed to a notable improvement of our manuscript. Below, we respond in detail to each of the suggestions and comments.
Associate Editor's comments (Dr Alecia Carter): We have included more detail in methods and results following each suggestion made, to give greater clarity and replicability to the manuscript. We have substantially changed the introduction, and also parts of the discussion, to incorporate information from the literature on UAS applications in terrestrial fauna suggested by the reviewers.
Reviewers' Comments to Author: Reviewer: 1 General comments 1.Thanks to the reviewer for the list of literature provided. We have substantially changed the introduction, and also parts of the discussion, to incorporate information from the literature on UAS applications in terrestrial fauna suggested by the reviewer. We have therefore focused on contrasting the progress achieved in evaluating the technical feasibility of the use of drones in wildlife in general, with the little progress in understanding the reaction of animals, highlighting mainly the few experimental studies that exist to date on terrestrial mammals. We have also modified the abstract according to those changes.
2. We have replaced the word "altitude" with the word "height" and "height AGL" throughout the text.

L324
We maintain "highlight" because we are referring to "these results" L328 We used "especially" L329-331 We rephrased the sentence. Table 1. We changed the presentation of the heights of HF for Feb 2018, but we also standardized the records in S and Sb, so as not to repeat heights. We believe that this way the table is better explained.