Bird Survival in Wind Farms by Monte-Carlo Simulation Modelling Based on Wide-Ranging Flight Tracking Data of Multiple Birds During Different Seasons

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

review summary

This paper is very valuable in the field of research on the effects of wind turbines on birds. The strong agreement between modelled probabilities and observed carcass data in this paper confirms that integrating high-resolution GPS tracking with systematic mortality monitoring can produce reliable collision risk estimates. This approach enables more precise, species-specific Environmental Impact Assessments (EIA's) and can inform targeted mitigation. The paper shows that realistic flight‑height distributions and seasonal behavior must be included in EIA's as much as possible. 

general concept comments

I have only a few general minor comments on the paper. I fully agree with the results, discussion, and conclusions.

-In the Introduction, some more recent references could be added (see specific comments below) including a minor adjustment to the sentence in connection with the described possible effects on populations.

-In the Materials & Methods, some minor clarifications can be made about the data collection (see specific comments), and in the data processing & modelling section, some more detail information could be valuable (and also see the question about the used Band model and possible more recent reference (see specific comments below). 

specific comments 

-lines 40, 42, 93, 94, 107, 109, 155, 248, 264, 266, 275, 279, 281, 287, 292, 296, 305: please always use the correct spelling for "Common Buzzard(s)" with capitals. On these lines variations were used like Common buzzard(s), and common buzzard(s).

-line 17, 30, 40: "low collision probability". I suggest "relatively low collision probability".

-line 40-42: I suggest to add "..., although continued monitoring is essential." like in the simple summary, or something like that. I think no detailed analysis was made for possible population effects, so in this case, this sentence could be nuanced a bit because of that.

-line 51-52: The statement about “no evidence” is quite sensitive, and in the paper based on an old reference (2001) from a stakeholder Committee and not a peer-reviewed paper (which would be better here). There are at least strong indications of negative impacts on some bird populations at local/regional scale. I suggest you change this sentence a little by stating that there is some evidence of possible negative population effects at local/regional scale. For some bird species (especially raptors) there is clear evidence, and in a few cases explicit demographic analyses, showing that collision mortality from wind turbines can cause population-level effects on local to regional scales. 

More detail info: A systematic review on raptors found evidence of lower abundance/declines after wind farm installation. For raptors, collision mortality is a relevant pressure and population-level impacts can occur, especially cumulatively (Estellés-Domingo & López-López 2024). For example, a recent analysis also found that further expansion of wind turbines could result in the local extinction of Cinereous Vultures and Griffon Vultures, depending on space use intensity (Bounas et al. 2025). A methodological paper on additional mortality limits in impact assessments concluded that collisions can affect bird populations and that cumulative impacts are important in decision-making (Schippers et al., 2020). Recent case studies and syntheses also highlight cumulative risks for certain seabird groups (not only collisions but also disturbance/avoidance), which can drive changes in regional population numbers (Garthe et al. 2023; Williams et al. 2024). Analyses further show that turbine specifications (e.g. larger rotor size) increase mortality in some species, raising the risk of population-level effects (Garvin et al. 2024).

List of references used above:

Bounas, A.; Vasilakis, D.; Kret, E.; Zakkak, S.; Chatzigiannakou, M.; Kapsalis, E.; Arkumarev, V.; Dobrev, D.; Stamenov, A.; Stoychev, S.; Skartsi, T.; Sidiropoulos, L.; Halley, J. Cumulative collision risk and population-level consequences of industrial wind-power plant development for two vulture species: A quantitative warning. Environ. Impact Assess. Rev. 2025, 110, 107669. https://doi.org/10.1016/j.eiar.2024.107669

Estellés-Domingo I. & López-López P. (2024). Effects of wind farms on raptors: A systematic review of the current knowledge and the potential solutions to mitigate negative impacts. Anim. Conserv. 2024, 28, 334-352. https://doi.org/10.1111/acv.12988

Garvin, J.C.; Simonis, J.L.; Taylor, J.L. Does size matter? Investigation of the effect of wind turbine size on bird and bat mortality. Biol. Conserv. 2024, 291, 110474, https://doi.org/10.1016/j.biocon.2024.110474

Garthe, S.; Schwemmer, H.; Peschko, V.; Markones, N.; Müller, S.; Schwemmer, P.; Mercker, M. Large-scale effects of offshore wind farms on seabirds of high conservation concern. Sci. Rep. 2023, 13, 4779. https://doi.org/10.1038/s41598-023-31601-z

Schippers, P.; Buij, R.; Schotman, A.; Verboom, J.; van der Jeugd, H.; Jongejans, E. Mortality limits used in wind energy impact assessment underestimate impacts of wind farms on bird populations. Ecol. Evol. 2020, 10, 6274-6287. https://doi.org/10.1002/ece3.6360

Williams, K.A.; Gulka, J.; Cook, A.S.C.P.; Diehl, R.H.; Farnsworth, A.; Goyert, H.; Hein. C.; Loring, P.; Mizrahi, D.; Petersen, I.K.; Peterson, T.; Press, K.M.; Stenhouse, I.J. A framework for studying the effects of offshore wind energy development on birds and bats in the Eastern United States. Front. Mar. Sci. 2024, 11, 1274052. https://doi.org/10.3389/fmars.2024.1274052

-line 55-65: You may add a more recent reference in this part with some new information (see remark in line 51-52), like the review paper from Estellés-Domingo & López-López (2024), and change the text a little, if needed.

-line 76 & 433-434 (references): I think the reference nr. 28 is wrong (looks like two different ones mixed). Probably this must be "Garvin, J.C.; Simonis, J.L.; Taylor, J.L. Does size matter? Investigation of the effect of wind turbine size on bird and bat mortality. Biol. Conserv. 2024, 291, 110474, https://doi.org/10.1016/j.biocon.2024.110474 
(see also my earlier remark for additional references)

-line 101, 121, 223: Maybe it's useful to also mention the latest reference for the Band model, from 2024, with more detail, depending on what was used in your analysis. Just a suggestion. Band, W. (2024). Using a collision risk model to assess bird collision risks for onshore wind farms. NatureScot Research Report 909. https://www.nature.scot/doc/naturescot-research-report-909-using-collision-risk-model-assess-bird-collision-risks-onshore-wind 

-line 110, 113; 304: "discovered" can be better replaced by "found".

-line 185 (table 2): About the "Bird flight type" in the table. "Breeding" seems also including during the winter period, and "Migratory" also seems including the breeding season. Please correct, or clarify. 

-line 190: The month "May" is already in the breeding season. Please clarify if needed. And is there a reason why no vantage point surveys were performed during breeding season?

-line 208-209: No searches were done during the breeding season? Table 3 in the results shows that they did. Please clarify/correct. 

-line 278: "in risk" can better be "at risk".

-line 284: "6MW", add space "6 MW"

-line 311, 346: "low" could best become "relatively low"

 

Author Response

We sincerely thank the reviewers for their constructive and insightful comments on our manuscript. We have carefully revised the text according to all suggestions and provided a detailed point-by-point response in the attached document. We believe the revised version has substantially improved in clarity, completeness, and alignment with the journal’s standards.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The authors present an interesting and contemporary study on the effects of wind turbines on bird survival, using a Monte Carlo simulation model to examine the impact on Common Buzzards (Buteo buteo). Clearly, this kind of research is necessary given the global need to increase clean energy production.

Using a multi-methodology approach involving long-term GPS tracking data, visual monitoring and carcass searches, the authors ran the Band Collision Risk model to determine collision probability based on turbine configuration. They concluded that there are differences between seasons and that, despite the low collision probability in the study area (Bulgaria), efforts should be made to optimise mitigation measures.

The research is well conducted, the methodology is adequate, and the results and conclusions align with the study's objectives.

In order for the MS to be accepted by the Birds journal, some minor changes should be made.

1. The location of the study is not mentioned in the abstract.
2. The first paragraph on page 3 (lines 54–56) should be rewritten, as it is difficult to read.
3. Line 112 should read 'with 114 operational wind turbines'.
4. Be careful with line 131.
5. The study area explanation (lines 141–144) is slightly confusing. Perhaps latitude and longitude are not necessary.
6. From the first mention of the target species (Common Buzzard, Buteo buteo), you should use the common name rather than the Latin name. Check this throughout the document.
7. Table 2 (page 6) is interesting and informative, but the file name column may be unnecessary.
8. Figure 6 (page 8) has a low resolution. Please add a file with a higher resolution so that the information can be seen correctly.
9. I have an issue with figures 9, 10 and 11. Could these be summarised in a table?

That's all. I enjoyed reading your research.

Author Response

We sincerely thank the reviewers for their constructive and insightful comments on our manuscript. We have carefully revised the text according to all suggestions and provided a detailed point-by-point response in the attached document. We believe the revised version has substantially improved in clarity, completeness, and alignment with the journal’s standards.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thanks for the minor revision of the paper. It looks better now, indeed. In the text of the discussion, I noticed that some new references are also listed with the name/year (not just the reference number), and some of the new references are not listed yet in the reference list. But I assume this will be corrected by the editors in the final version.

s will be corrected by the editors.

 

, 

I noticed that some new references in the text are also listed with the name and year (not just the reference number), but I assume this will be corrected by the editors.

Author Response

Dear Reviewer,

Thank you very much for your positive evaluation and for acknowledging the improvements in the revised version. Regarding your note on the newly added references, we have now checked the text carefully and corrected all instances where author–year citations appeared. All references are consistently numbered and included in the reference list, in line with the journal’s guidelines.

We appreciate your careful reading and constructive comments throughout the review process.

Best regards,
Nikolay Yordanov (on behalf of all co-authors)