Assessing the Behavioural Responses of Small Cetaceans to Unmanned Aerial Vehicles

Round 1

Reviewer 1 Report

Dear authors,

I was pleased to review your manuscript and I believe that it has merit. In particular, I appreciated the choice to test the response to the drone approach.

My main concern is the statistical approach chosen to analyse the data and its limitations which are not negligible. Whether you will decide or not to choose an alternative statistical approach, I would refine the presentation of the statistical method and justify the exclusion of some variables that might have influenced your results. For instance, environmental factors such as the sea state can mask the noise of the propellers and affect the dolphin response. Furthermore, the behavioral state during the exposure can affect the response, as you briefly mentioned in the discussion section. What about the pod size and composition? Where calves present in each sampled pod or not? I think that these aspects should be carefully addressed in the discussion section, especially if they were not tested in your statistical approach.

Kind regards

 

Here are some line specific comments:

Line 2: The word "impact" implies the presence of consequences, generally negative, on the species object of the study. "Responses" or "reactions" would be more appropriate in this case.

Line 2: As you correctly mentioned in the introduction, an Unmanned Aerial System is composed by an Unmanned Aerial Vehicle, a ground station and, eventually, a launching/retrieving mechanism. I think it would be more correct (and clear for the readers) to use Unmanned Aerial Vehicles (UAVs) here and throughout the manuscript.

Line 14: Some UAS are far from being cheap, even in comparison with manned aircraft. Might be better to use adjectives such as "relatively affordable" when price tags are not specified.

Lines 14-17: I would add a reference to "morphometric studies" (photogrammetry). "Small groups of animals" contradicts "demographic" and it is not completely true as, depending on the flight altitude, it is possible to count hundreds of individuals in a single frame.

Line 23: Maybe "dropping" should be replaced by "lowering/descending"

Line 32: I would use keywords which are not present in the title.

Lines 37-41: I think that some of these information are quite general and not relevant for the scope of the manuscript. Moreover, it is still under debate that UAS reduce "drastically" the financial costs in comparison to manned aerial surveys, especially for abundance surveys on vast areas.

Line 43: Again, I would be more cautious > "relatively inexpensive"

Line 45: Maybe "larger" could be replaced with "fixed wing" as the type of flight is the main limiting factor for VTOL UAVs in terms of battery endurance and carrying capabilities.

Line 49: You can add "morphometric" here.

Line 53: I would add other species/references e.g. dusky dolphins, finless porpoises (Morimura & Mori, 2019), Southern Right Whales (Nielsen et al 2019; Christiansen et al 2018, 2019)

Line 56: ...scarce and limited. Maybe add "to a few species"

Lines 75-78: What are the hypotheses of the study? Is your study design and statistical method able to quantify/measure the response? 

Lines 103-105: Maybe this sentence needs to be backed up by a reference or better justified. What if two or more directional changes take place in a 30 seconds interval? How you can quantify this when your dependent variable is 0-1?

Lines 112-113: Behavioral states were assessed prior and during the experimental setup. Did any behavioral change took place during the flights? Why were behavioral states not tested as independent variable?

Lines 121-122: Why you did not consider to use the UAV video to extract the response data post hoc?

Lines 144-146: Therefore, dolphins changed direction equally at 5, 20 and 30 m? How would you explain such result?

Lines 157-160: It seems that the first sentence contradicts the second one.

Line 163: >= 10 m for common dolphins, >= 5 m for bottlenose dolphins.

Line 164: more than "feasibility", results suggest the UAV potential as "non invasive" tool for the behavioral of dolphins.

Line 181: Why the influence of behavioral state was not tested, at lest for common dolphins?

Line 187-189: I recall that this observation was related to the UAV shadow cast on the dolphin body.

Line 193-195: It is a bit confusing here as behavioral events are not behavioral states (which were not tested in your study).

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Uncrewed aircraft systems (UAS) are a relatively novel field that is becoming more mainstream for marine mammal assessments. This manuscript provides an important assessment on the effects of UAS surveys over two dolphin species. As the literature on disturbance impacts upon marine mammals by UAS are sparse, this manuscript will be a valuable contribution to literature, especially for common dolphins for which there are no previous studies in the literature. The authors present a robust study design, thoroughly describing dolphin behaviors prior to, and after, UAS interactions. This qualitative and quantitative design represents the behavior tracking and outcomes well.

The abstract uses the term UAS and the text seems to use the terms UAS and UAV more consistently—In my experience, these two terms are used interchangeably and I suggest the authors use the term of their preference throughout the document for consistency. When distinguishing the UAS components, in our office, we usually refer to them as the UAS platform, radio controller, and ground control station.  

This manuscript may benefit from mentioning two caveats or limitations to this study:

1. These dolphin populations are habituated to regular whale watching presence nearby which could greatly contribute to their lack of reaction and caution should be taken with any new population regardless if it is the same species.
2. That the UAS platform used was a small VTOL platform and variation in size and power of other VTOLs could illicit vastly different responses from populations, especially those in more remote areas with lesser human presence.

Comments and suggestions by line: 

Line 22: this line states that the initial height was 50m but the methods states 70-100m

Line 38: “….a video camera payload carried aboard the UAV and a ground…” suggest using “mounted to the UAV and a ground…”

Line 44: “…highly manoeuvrable platform…” maneuverable is misspelled.

Line 44: “…of single individuals or…” Suggest “of an individual or….”

Line 45: this sentence is unclear as written, “Nonetheless, in comparison to boats, manned aerial surveys and larger…”

Line 48: “… VTOL UAV’s present an excellent…” suggest “VTOL UAV’s are an excellent…”

Line 49: “… behavioural and demographic studies” suggest including abundance surveys (and supporting citations), as well

Line 59: “…This may be due to association with avian predators that cast a shadow of similar size to the UAV’s when at certain altitudes [2,11,12].” This suggests that there are avian predators of the aforementioned seal species? The cited text don’t seem to support this specific claim. Later, the authors describe the hearing of cetaceans and therefore the effects of UAS sound propagation however, there is no connection between the visual acuity of the aforementioned seal species so such a statement seems unsupported. Suggest the authors adding more supporting statements to this section.

Line 189: interesting point about the side eye swimming being a possible indicator for future studies!

Line 195: Suggest also discussing that these populations of dolphins inhabit areas that experience high activity from whale watching boats therefore, they are likely less reactive than those populations that live in more remote areas and the results of this study should be referred to with caution, as well for such secluded populations. Would include this detail in the abstract, as well.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Dear authors,

I appreciated the comments' rebuttals and amendments. I believe that your note can be published after some minor edits. 

I think there was a misunderstanding about my question about testing behavioral states' influence on the dependent variable. The behavioral state at time of exposure to the UAV test might affect your response variables (as you mentioned at lines 210-216) and that is why I asked if the effect of this factor was investigated (as independent variable/factor and not as dependent variable, which makes little sense, as you stated in your reply). For instance, I would expect socializing or foraging dolphins to change speed/direction/diving behavior more frequently than travelling dolphins. I understand that the low sample size might not allow to use modelling tools to investigate this aspect and eventually pool pods in different behavioral states to analyse them separately (the same observation is valid also for the other factors that were not included in the statistical analysis).

Here are line specific comments:

Lines 59-64: Check referencing here and throughout the text e.g., REF#8 is not an abundance study but a dedicated UAV disturbance test like yours.

Lines 82-87: Quite confusing here as two of the references you indicated are actually on small cetacean species (bottlenose dolphins) and found significant responses of the dolphins exposed to the UAVs flying over them.

Lines 241-242: I think here there is the misunderstanding I mentioned above. Those factors should be tested as independent variables, not as response. As you stated in the reply to the comments, it does not make much sense to look at behavioral state changes (which you did not observe) with your methodological approach, neither I would expect to observe changes in pod composition/size in the space of only 30 seconds. Instead, pod size, pod composition, behavioral state at the time of exposure can influence your findings and should be indicated as potentially confounding factors.

Lines 254: Still you observed a response by common dolphins. I would reinforce this finding here as it is a significant result of your study and it justifies your recommendations for a cautious approach to the use of UAVs in cetacean research and professional/recreational filming.

I wish you the best for the coming festivities

Kind regards

Author Response

Please see the attachment.

Author Response File: Author Response.docx