Assessment of Ground and Drone Surveys of Large Waterbird Breeding Rookeries: A Comparative Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this paper, the authors address the important problem of comparing ground-based and drone-based observations for assessing abundance and determining timing in the phenological cycle of waterbirds.

This problem has been in the literature almost from the very beginning since drones began to be used for this purpose. What the authors have accomplished improves our knowledge on the subject, and for this reason the work is likely to be published. Unfortunately, in many points, mainly methodological, but also in the transmission of content, it raises my doubts.

1. The first issue is that the ground observations and those made from the drone were not made on the same day (see Figure 2). In this case, I have a question, how can the results obtained be compared and then inferred from them, as the authors did?

2. The comparison photos shown in the table 2 may be misleading. Taking a photo of eggs or a nest from a camera that the observer has with him/her from a distance of 1 m will always be better with today's technology than a photo taken from a drone. In addition, there is no information on what camera and with what lens the photo from the ground was taken?

3. In the case of photos taken from drones, this information (camera, lens) is also essential. There is a lot of work, e.g. Fudala and Bialik (2022), which evaluates the amount of marine birds depending on the height of the drone, thus the pixel size, minimizing the impact on birds, or Weimerskirch et al. (2018) which investigated seabirds specific behavioural and physiological responses to drones. I suggest to at least look through these works.

But, here the question arises whether 20 meters or less is not too low an altitude in drone use? Does it comply with ethical principles? Did the authors have permission to do so?

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript shows interesting information about the use of drones for understand the breeding ecology of waterbirds breeding in a complex habitat to be surveyed. The contrast between two methodologies highlights the increasing precision of drone surveys, however showing the importance of ground surveys to get other information impossible to take by the drone. I think the manuscript is well developed, Figures are all interesting, results and discussion are well presented, introduction probably could be improved.

Introduction

It is a quite short introduction; authors should introduce the lectors citing more articles. It could be useful to introduce the readers using and citing a wide diverse of ecology research done using drones in several group of vertebrates.

Lines 56-58: should be erased, is unnecessary

Figure 1. I like this figure but it should show also the whole country, it is difficult to understand which part of Australia authors are showing.

Drone survey: Drone characteristics are poorly explained, authors should mention trademark (DJI?), model, weight, color, sound. Did authors use some kind of app to fly?

Breeding success it is a really difficult goal to rich when you study this kind of colonies with mobile individuals while their close to fledge. You should mention all the limitation on this procedure. I really believe this measure is very out of precision…  

Line 118: “per nest” is repeated twice

Line 201: Authors assume all drones have the same cameras…

Line 207-208: If authors mention scarce behavioral responses of birds to drones, they should mention that several species could react intensely against drone presence. Several cites should be mention about it, to complement the phrase. Many researchers could be incentivized to use drones after reading this article, so I believe some articles considering reactions against drones should be mention as an informative warning:

Brisson-Curadeau, É.; Bird, D.; Burke, C.; Fifield, D.A.; Pace, P.; Sherley, R.B.; Elliott, K.H. Seabird species vary in behavioral response to drone census. Sci. Rep. 2017, 7, 17884.

Mesquita, G.P.; Rodríguez-Teijeiro, J.D.; Wich, S.A.; Mulero-Pázmány, M. Measuring disturbance at a swift breeding colonies due to the visual aspects of a drone: A quasi-experiment study. Curr. Zool. 2020, 67, 157–163.

Frixione, M.G.; Salvadeo, C. Drones, Gulls and Urbanity: Interaction between New Technologies and Human Subsidized Species in Coastal Areas. Drones 2021, 5, 30.

Weimerskirch, H., Prudor, A., & Schull, Q. (2018). Flights of drones over sub-Antarctic seabirds show species-and status-specific behavioural and physiological responses. Polar Biology, 41, 259-266. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The paper has been improved according to my comments. In the current version it can be published. I do not have additional doubts.