The Decline of Common Birds Exemplified by the Western Jackdaw Warns on Strong Environmental Degradation

Round 1

Reviewer 1 Report

The manuscript conservation-1553135 „The Decline of Common Birds Exemplified by The Eurasian Jackdaw Warms on Strong Environmental Degradation” is excellent written and provides strong evidence of population decline of  Eurasian Jackdaw due to anthropogenic land-use intensification during the last decades in central Spain. The scientific gap is defined in the introduction part, since a scientifically based empirical assessment of the population trends is missing, especially in a bird species, which may subjectively  are abundant.  A combination of quantitative and qualitative date have been used and statistical examined for assessment of the population trends. The decline of the western jackdaw in central Spain in the last few decades was shown by the statistical analysis and appropriately presented in tables and figures. The discussion is well structured and shows various anthropogenic influences as a result of the intensification of land use in the context of the scientific evidence, supported by the numerous references. Overall, a well-written manuscript with no need for corrections or inquiries.

Author Response

Thank you very much for your positive comments

Reviewer 2 Report

This is a useful and informative paper that shows how conservation of common species is important to promote wider biodiversity conservation and ensure that all species can thrive. The authors have provided a detailed and repeatable method. I recommend this paper for publication if the following questions are answered and addressed to improve clarity. 

I'm not sure that I understand the title of the paper. Is the word "Warms" correct? Should this be warns?

Abstract

Line 23: best to not start a sentence with "Because..."

Line 29: Is lack the correct word? Reduced breeding in riparian forests?

Line 40: Suggest "Generally, it seems that high-intensity agricultural 
management more drastically affects smaller and less resilient common species..."

Introduction

Line 94: why largest? Largest commonly seen birds? Or largest in terms of those persecuted? I don't understand the context here.

Line 101: is black corvid an accepted definition of a group of these species?

Line 118: best to not start a sentence with "Because..."

Line 120: "... whose population trends..."

I think you need to define resilience. What makes some common birds less resilient than others?

Methods

Line 125/126 needs a reference

Line 127 needs a reference

Line 152: Please define what gypsophilous scrubland is

For all species names (when first mentioned) in the text please provide the scientific name, e.g. holm oak, ash, olive etc.

Please define what you mean by riparian forest.

Figure 1: the legend on the figure explaining the different colours is very hard to read.

Line 228: what limitations? Please explain

Line 299: "... subject to..."

Statistical analysis

Very thorough and easy to follow.

Please provide the name of the statistical package used for data analysis (and a citation).

How was model fit checked? 

Line 255: please explain which data were included in the KW test.

Results

I would recommend using a Benjamini-Hochburg correction when comparing multiple P values to avoid false discovery. Likewise for Table 3.

Figure 3: What happens if you re-draw without the outliers? It is very hard to see the trend in data currently. 

Discussion

Line 383 Perhaps the jackdaws are being squeezed out of these foraging sites by larger birds that can easily outcompete smaller species?

Line 401: How do you mean cattle farming is reduced but intensified? I.e. fewer farms overall but these farms have more cattle on them?

Line 497: avoid starting a sentence with "Because..."

Line 498: I would refer to the jackdaw by name in the conclusion so the reader is aware of which bird you are discussing. 

Line 500: Are jackdaws of a relatively large size? Compared to what?

You also say that the jackdaw is medium sized in your methods section.

Line 507: "... when agricultural practices..."

Please provide information on ethical review of methods. 

Please provide a data availability statement for the raw data files.

Author Response

This is a useful and informative paper that shows how conservation of common species is important to promote wider biodiversity conservation and ensure that all species can thrive. The authors have provided a detailed and repeatable method. I recommend this paper for publication if the following questions are answered and addressed to improve clarity. 

I'm not sure that I understand the title of the paper. Is the word "Warms" correct? Should this be warns?

Authors’ response: Yes, this is a typo. It should read warn as the reviewer rightly points out.

Abstract

Line 23: best to not start a sentence with "Because..."

Authors’ response: we have changed the sentence so that it does not start with “Because”, as recommended by the reviewer.

Line 29: Is lack the correct word? Reduced breeding in riparian forests?

Authors’ response: We have changed the sentence to avoid the term “lack” as we have not covered all riparian forests in the study area.

Line 40: Suggest "Generally, it seems that high-intensity agricultural 
management more drastically affects smaller and less resilient common species..."

Authors’ response: We have included the reviewer's suggested changes to this sentence.

Introduction

Line 94: why largest? Largest commonly seen birds? Or largest in terms of those persecuted? I don't understand the context here.

Authors’ response: We refer to body size. We have changed the erroneous term "largest" to "biggest".

Line 101: is black corvid an accepted definition of a group of these species?

Authors’ response: we have removed the term "black" as it is not an accepted generic term, as the reviewer rightly points out.

Line 118: best to not start a sentence with "Because..."

Authors’ response: we have changed the sentence so that it does not start with “Because”, as recommended by the reviewer.

Line 120: "... whose population trends..."

Authors’ response: we have changed the sentence as recommended by the reviewer

I think you need to define resilience. What makes some common birds less resilient than others?

Authors’ response: we have changed "resilient" to "adaptable" throughout the manuscript because it better reflects the ability of species to withstand anthropogenic changes in the environment.

Methods

Line 125/126 needs a reference

Authors’ response: we have included a general reference as suggested by the reviewer.

Line 127 needs a reference

Authors’ response: the same general reference where a lot of information and other references are given has been cited several times in the same paragraph, so perhaps it is not necessary to refer to it in every sentence, bearing in mind that it is general information on the species that can be found in any European bird handbook.

Line 152: Please define what gypsophilous scrubland is

Authors’ response: It refers to scrubland growing on soils composed of gypsum. We have specified it in the text as suggested by the reviewer

For all species names (when first mentioned) in the text please provide the scientific name, e.g. holm oak, ash, olive etc.

Authors’ response: Done.

Please define what you mean by riparian forest.

Authors’ response: we have changed the term "riparian" to "riverside".

Figure 1: the legend on the figure explaining the different colours is very hard to read.

Authors’ response: we have made some modifications to the legend to try to make it clearer, as recommended by the reviewer.

Line 228: what limitations? Please explain

Authors’ response: in the line indicated by the reviewer, there is no text referring to limitations. Perhaps the reviewer is referring to line 258 where it refers to logistical limitations. We have specified these limitations in that part of the text, on the understanding that it is an error in the line number.

Line 299: "... subject to..."

Authors’ response: corrected

Statistical analysis

Very thorough and easy to follow.

Please provide the name of the statistical package used for data analysis (and a citation).

Authors’ response: We have included the statistical package used (glmmTMB package) and a corresponding reference (Brooks ME, Kristensen K, van Benthem KJ, Magnusson A, Berg CW, Nielsen A, Skaug HJ, Maechler M, Bolker BM (2017). “glmmTMB Balances Speed and Flexibility Among Packages for Zero-inflated Generalized Linear Mixed Modeling.” The R Journal, 9(2), 378–400).

How was model fit checked? 

Authors’ response: The fit of the models was evaluated using the package DHARMa (Hartig, 2018), now included in the text and reference list, respectively. Hartig F. 2018. DHARMa: Residual Diagnostics for Hierarchical (Multi-Level/Mixed) Regression Models. R Package. https://cran. r-project. org/package=DHARMa, Version 0. 2. 0.

Line 255: please explain which data were included in the KW test.

Authors’ response: we have specified the response variable (number of jackdaws in each roost: roost size) and the independent variable (census year).

Results

I would recommend using a Benjamini-Hochburg correction when comparing multiple P values to avoid false discovery. Likewise for Table 3.

Authors’ response: We have used the Benjamini-Hochberg correction for multiple tests in our comparisons following the reviewer’s comment. All tables were updated.

 

Figure 3: What happens if you re-draw without the outliers? It is very hard to see the trend in data currently. 

Authors’ response: Done

Discussion

Line 383 Perhaps the jackdaws are being squeezed out of these foraging sites by larger birds that can easily outcompete smaller species?

Authors’ response: This does not seem to be the case because these species were already very abundant in the garbage dumps when jackdaws were also abundant in the past. That is why in the text we said that these species have continued to use the dumps.

Line 401: How do you mean cattle farming is reduced but intensified? I.e. fewer farms overall but these farms have more cattle on them?

Authors’ response: we mean that its distribution range has been reduced but intensified in management. We have added these clarifications in the new version of the manuscript.

Line 497: avoid starting a sentence with "Because..."

Authors’ response: we have changed the sentence so that it does not start with “Because”, as recommended by the reviewer.

Line 498: I would refer to the jackdaw by name in the conclusion so the reader is aware of which bird you are discussing. 

Authors’ response: Done

Line 500: Are jackdaws of a relatively large size? Compared to what?

You also say that the jackdaw is medium sized in your methods section.

Authors’ response: we refer to it as a relatively large species among common birds. We have specified this in the new version

Line 507: "... when agricultural practices..."

Authors’ response: corrected.

Please provide information on ethical review of methods. 

Authors’ response: All data included are observational.

Please provide a data availability statement for the raw data files.

Authors’ response: All information included has been extracted from the appropriately cited literature, or is provided in the tables and figures.