Mammal Fauna Changes in Baltic Countries During Last Three Decades

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Very interesting detailed analysis showing population trends for all mammal species in three Baltic countries. Perhaps it could be possible to identify more precisely reasons for sharp population decline in some cases and  rapid increase of some other species. Some human related environmental changes can be either detrimental or beneficial depending on the species and it would be interesting to show those relations.

The paper would benefit from including few more maps showing distribution of the most endangered species and their possible connections with home ranges of those species in neighbouring countries.

Comments for author File: Comments.pdf

Author Response

Reviewer 1 comments and answers

Comment: Very interesting detailed analysis showing population trends for all mammal species in three Baltic countries. Perhaps it could be possible to identify more precisely reasons for sharp population decline in some cases and rapid increase of some other species. Some human related environmental changes can be either detrimental or beneficial depending on the species and it would be interesting to show those relations.

Answer: We appreciate your comment and fully agree that identifying specific human-related environmental changes that either negatively or positively impact mammal populations is critical for understanding the broader trends. We would like to clarify that this is a review paper, and while we do not provide new empirical analyses, we do address presumed causes of population change in detail in Section 4.5, Presumed Drivers of Recent Changes.

In this section, we synthesize findings from previous research and monitoring to highlight key drivers influencing mammal population dynamics in the Baltic region. These include historical and contemporary human-related factors such as:

• Increased forest cover and intensified forest management, driven by large-scale land abandonment and natural afforestation since 1991, especially in eastern Latvia.
• Fragmentation of mature forests due to intensified forestry and the proliferation of forest roads (e.g., 7700 km constructed in Latvia since 2003).
• Infrastructure development, including major projects like Via Baltica and Rail Baltica, as well as border fences, which restrict large mammal movement and contribute to habitat fragmentation.
• Climate change and globalization of wildlife diseases, which have led to changes in species distributions, competition, and mortality.
• Expansion of renewable energy infrastructure, particularly wind energy, which poses a growing but under-researched threat to bat populations.

We also present species-specific examples of how these factors interact:

• M. avellanarius benefits from current forest management.
• L. timidus and M. erminea are declining due to increased predation and climate change.
• C. aureus is expanding due to climate change and land abandonment.
• U. arctos is recovering, benefiting from rural depopulation and intensified forestry creating suitable habitats.

We believe these examples illustrate how certain human activities can have dual effects—benefiting some species while negatively impacting others—depending on species-specific ecological traits. We hope this framework helps clarify the complex interplay between anthropogenic drivers and mammal population trends in the region.

 

Comment: The paper would benefit from including few more maps showing distribution of the most endangered species and their possible connections with home ranges of those species in neighbouring countries.

Answer: we included map of the flying squirrel, Pteromys volans, indicating range decrease as Supplement Figure S1.

Additional comments: The main issue described in this paper are long term changes in population numbers of mammal species in three Baltic countries in the context of climate changes, land cover transformation and anthropogenic pressure.

In my opinion the topic is original (I do not know similar reports from this region) so it fulfils important gap.

There was the lack of similar elaborations from this region, so in my opinion this report provides very important overview of the trends in mammal populations.

I do not see any need for improvements of methodology, the authors seem to explore all available sources of information.

In conclusions, the authors have identified presumed drivers of changes in population numbers and indicates similar patterns occurring in neighbouring countries. Since the paper is not experimental and did not require initial hypothesis, its main issue is adequately presented.

In my opinion the references cited in the paper are appropriate and I do not have additional comments on the tables and figures.

Answer: thank you for understanding this is a review paper! We used all available references concerning Baltic and presented identified presumed drivers of changes in population numbers.

Reviewer 2 Report

Comments and Suggestions for Authors

Review

I have read the manuscript with great interest and must say that this work by the authors deserves the highest praise. Unlike many modern works, this study is based on real reliable data on the distribution of mammals in the region. It is necessary to note the very thorough and consistent approach of the authors to the formation of the primary database and the deep analysis of literature and other resources to obtain reliable information. The work done by the authors undoubtedly makes a very significant contribution to current knowledge in the field of ecology and nature conservation in Eastern Europe.

The article is provided with a very extensive bibliography. In many respects, the presented materials can be used as a good summary of the population dynamics of a number of species, which is important in the conservation and game and hunting business. The approach chosen by the authors to grouping species according to the characteristics of their population dynamics and ecological status also looks advantageous.

Also, I strongly recommend that you provide as an Appendix a file with the geographic coordinates of the observation points of the animals that appear in this study. Or a link to a database of such points, for example, in GBIF or similar.

 

 

Affiliation (one of Authors) Certified mammalian expert;

Expert? Certified? Who certified it and for what kind of expertise? Please provide the certification organization information or use general established for these cases term "Independent researcher, without affiliation"

 

Materials and Methods

Lines 156-166

Although the general approach to the analysis is clear, I still do not quite understand how the authors processed the geographical distribution of data on the territory? Which areas were established, how were the dynamics of areas and population density, individual random finds assessed? A detailed description of these points needs to be added to the section.

 

Results

Generally.

For all species, please indicate the full Latin species name at the first mention in the text (excluding tables).

Figure 2 and 3

Here, in the figure caption, you need to indicate the source of the data.

 

Neomys anomalus|milleri.

Authors should still decide on the accepted name and use only one of them everywhere, preferably the more correct Neomys milleri

Comments for author File: Comments.pdf

Author Response

Reviewer 2 comments and answers

Comment: I have read the manuscript with great interest and must say that this work by the authors deserves the highest praise. Unlike many modern works, this study is based on real reliable data on the distribution of mammals in the region. It is necessary to note the very thorough and consistent approach of the authors to the formation of the primary database and the deep analysis of literature and other resources to obtain reliable information. The work done by the authors undoubtedly makes a very significant contribution to current knowledge in the field of ecology and nature conservation in Eastern Europe.

Answer: thank you for the positive evaluation.

 

Comment: The article is provided with a very extensive bibliography. In many respects, the presented materials can be used as a good summary of the population dynamics of a number of species, which is important in the conservation and game and hunting business. The approach chosen by the authors to grouping species according to the characteristics of their population dynamics and ecological status also looks advantageous.

Answer: thank you.

 

Comment: Also, I strongly recommend that you provide as an Appendix a file with the geographic coordinates of the observation points of the animals that appear in this study. Or a link to a database of such points, for example, in GBIF or similar.

Answer: we understand your desire, however there are several reasons this cannot be done:

1. The authors are obliged to include this in the European Mammal Atlas ver 2, which has not yet been published, but the distribution data are presented.
2. Data we used are available in the mentioned databases, so we cannot re-publish these
3. Links to all used information sources are present in the paper.

 

Comment: Affiliation (one of Authors) Certified mammalian expert; Expert? Certified? Who certified it and for what kind of expertise? Please provide the certification organization information or use general established for these cases term "Independent researcher, without affiliation"

Answer: Valdis Pilats is certified at Latvian Nature Conservation Board, see https://www.daba.gov.lv/lv/katalogs?sugas__catalog_vid_1[425]=425

And it says (available in attached PDF file)

We revised as “Certified mammalian expert (certificate No. 042, Nature Conservation Board, Latvia); valdispilats@gmail.com “, though we need further consultation with MDPI, if change we did to the affiliation is correct

Materials and Methods

Comment: Lines 156-166, Although the general approach to the analysis is clear, I still do not quite understand how the authors processed the geographical distribution of data on the territory? Which areas were established, how were the dynamics of areas and population density, individual random finds assessed? A detailed description of these points needs to be added to the section.

Answer: we add text to 2.3: The geospatial data stored in the aforementioned national databases was initially evaluated and prepared for the needs of the EMMA2 (European mammal atlas) project using GIS tools. For this study, the same data were then compared across all three Baltic states, as well as with the geospatial data used for the EMMA1 maps and the previous study (Timm, 1998). A 50×50 km grid was used for both EMMA1 and EMMA2. In the databases, either a 10×10 km grid or coordinates are available.

The population numbers in sections 3.2 and 3.3 were used at the country level. We added Supplementary Table 1, which includes data on some game species. We would like to clarify that this is a review paper and that we do not provide new empirical analyses. Therefore, we did not "establish areas." Decreases in distribution were measured by comparing the number of occupied grid cells reported in Timm et al. (1998) with the number reported in the current study. This approach allowed us to standardize changes across the Baltic countries and species despite the varying national monitoring frameworks and national databases referred in Material and Methods section.

 

Comment: For all species, please indicate the full Latin species name at the first mention in the text (excluding tables).

Answer: Our experience publishing with various MDPI journals shows that (1) the full species name must be used the first time it is mentioned, but (2) tables are not specifically excluded.

Consulting the publication practices of other publishers shows that introducing a species name for the first time in a table can work if the table is prominently placed and clearly referenced before any abbreviated form appears in the text. This is the case for us. We placed the full species names in Table 1 so that readers would know what taxonomy we use. Species names used before Table 1 are presented in full. Therefore, readers will encounter the full name before seeing any abbreviations.

 

Comment: Figure 2 and 3, Comment: Here, in the figure caption, you need to indicate the source of the data.

Answer: Data on the number of game animals were drawn from official sources: Game animal census in Lithuania [33], Game animal populations in Latvia [34], and Status of Game Populations in Estonia [35], now indicated in the caption.

 

Comment: Neomys anomalus|milleri. Authors should still decide on the accepted name and use only one of them everywhere, preferably the more correct Neomys milleri

Answer: as N. anomalus was species name at the time of identification, reflected in publications, we acknowledge your comment with revision of Line 333: Since the 1990s, one insectivorous mammal, N. milleri (N. anomalus at that time),

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Here are some suggestions I have for this article, which I hope will be helpful to the author:

1.Lines 66–68. By 2050, the habitats of European mammals are expected to lose approximately 10%. Is there any reference to support this statement? Please provide additional explanation.

2.Lines 83–91. Is there a necessary connection between “developmental differences between countries” and “the emergence of research projects”? The logic between the sentences is not very smooth, and there is no obvious connection between the context. Additionally, what is the connection between the types of research projects listed in this paragraph and the article's theme of “changes in mammal community structure”? Please provide a detailed explanation. If this paragraph does not have a necessary reason for existence, it is recommended that the author delete it.

3.Line 94. The article mentions “summarizing changes in mammal composition while considering climate uncertainty and habitat conversion,” which suggests that the subsequent analysis will incorporate data on relevant climate factor changes and combine climate factors with community composition analysis. However, the article's methodology does not mention any climate-related data collection. I would like to know what the authors mean by considering climate uncertainty here, and I hope the authors can explain in detail what scientific questions are raised and addressed in this article.

4.Lines 97–105. The article uses an entire paragraph to introduce the historical evolution of the Baltic Sea region, which seems to have no connection to the main focus of the study (changes in mammal populations). It is recommended that this section be revised.

5.Lines 131-134. The article mentions the use of relevant scientific publications, but what are the criteria for selecting these publications? I suggest that the authors provide a detailed explanation of this aspect.

6.Line 138. The authors mention that some data that cannot be found online were collected from official websites. I would like to know what kind of sources these official websites refer to? National libraries? Or what kind of official websites? This involves the reliability of data sources, and I hope the authors can provide a detailed explanation of this issue.

7.The title of Section 2.2 is “Data Sources,” but I am not clear on what types of data the authors ultimately collected. Species distribution data? Species lists for each region? Or other types of data? Additionally, the authors analyzed changes in mammals over a 30-year period, which would require data on the structure of mammals across different years. What is the time interval between data from different periods? Five years, ten years, or something else? I suggest the author explain these issues in the paper.

8.I noticed that the data mentioned by the author cannot be found online, and there are no supplementary materials providing any data. This means that relying solely on the data mentioned in the paper is insufficient to reproduce the results, which significantly undermines the paper's credibility. I suggest the author carefully reconsider the way they present the data and materials.

9.The article does not appear to mention appropriate statistical analysis of the data, nor does it provide detailed explanations of how the data was processed after collection. It merely mentions the use of CAGR to calculate animal populations, which does not sufficiently justify the subsequent results. It is recommended that the authors provide detailed supplementary information.

10.The results section of the article reads more like a “discussion” section rather than actual “results.” It is recommended that the authors refer to relevant literature on the subject and rewrite the results section accordingly.

Author Response

Reviewer 3 comments and answers

Here are some suggestions I have for this article, which I hope will be helpful to the author:

Comment: 1 .Lines 66–68. By 2050, the habitats of European mammals are expected to lose approximately 10%. Is there any reference to support this statement? Please provide additional explanation.

Answer: it is [12], presented in Line 70.

 

Comment: 2.Lines 83–91. Is there a necessary connection between “developmental differences between countries” and “the emergence of research projects”? The logic between the sentences is not very smooth, and there is no obvious connection between the context. Additionally, what is the connection between the types of research projects listed in this paragraph and the article's theme of “changes in mammal community structure”? Please provide a detailed explanation. If this paragraph does not have a necessary reason for existence, it is recommended that the author delete it.

Answer: To acknowledge your comment we revised text accordingly: Due to differences in research history and capacity across the Baltic countries, data coverage is uneven. These differences have resulted in variations in long-term and synthesis projects, including Red Data and Red Books, studies on invasive species, analyses of roadkill, monitoring of mammals, and population replenishment through breeding. For instance, extensive long-term monitoring exists for large ungulates, yet sparse records exist for small insectivores, carnivores, and bats. Therefore, analyses of community-structure shifts must account for these gaps. For instance, there is limited small-mammal data in Latvia, and bat surveys are lacking in Lithuania. Some existing information remains at the expert level.

 

Comment: 3.Line 94. The article mentions “summarizing changes in mammal composition while considering climate uncertainty and habitat conversion,” which suggests that the subsequent analysis will incorporate data on relevant climate factor changes and combine climate factors with community composition analysis. However, the article's methodology does not mention any climate-related data collection. I would like to know what the authors mean by considering climate uncertainty here, and I hope the authors can explain in detail what scientific questions are raised and addressed in this article.

Answer: We would like to clarify that this is a review paper, and while we do not provide analyses, we do address presumed causes of population change in detail in Section 4.5, Presumed Drivers of Recent Changes.

In this section, we synthesize findings from previous research and monitoring to highlight key drivers influencing mammal population dynamics in the Baltic region. These include historical and contemporary human-related factors such as:

• Increased forest cover and intensified forest management, driven by large-scale land abandonment and natural afforestation since 1991, especially in eastern Latvia.
• Fragmentation of mature forests due to intensified forestry and the proliferation of forest roads (e.g., 7700 km constructed in Latvia since 2003).
• Infrastructure development, including major projects like Via Baltica and Rail Baltica, as well as border fences, which restrict large mammal movement and contribute to habitat fragmentation.
• Climate change and globalization of wildlife diseases, which have led to changes in species distributions, competition, and mortality.
• Expansion of renewable energy infrastructure, particularly wind energy, which poses a growing but under-researched threat to bat populations.

We also present species-specific examples of how these factors interact:

• M. avellanarius benefits from current forest management.
• L. timidus and M. erminea are declining due to increased predation and climate change.
• C. aureus is expanding due to climate change and land abandonment.
• U. arctos is recovering, benefiting from rural depopulation and intensified forestry creating suitable habitats.

We believe these examples illustrate how certain human activities can have dual effects—benefiting some species while negatively impacting others—depending on species-specific ecological traits. We hope this framework helps clarify the complex interplay between anthropogenic drivers and mammal population trends in the region.

 

Comment: 4.Lines 97–105. The article uses an entire paragraph to introduce the historical evolution of the Baltic Sea region, which seems to have no connection to the main focus of the study (changes in mammal populations). It is recommended that this section be revised.

Answer: to define study site, we suppose it is not enough to say “the Eastern Baltic Region” or “the Baltic”. To acknowledge your comment, we revised mentioned chapter and significantly shortened it.

 

Comment: 5.Lines 131-134. The article mentions the use of relevant scientific publications, but what are the criteria for selecting these publications? I suggest that the authors provide a detailed explanation of this aspect.

Answer: We agree that clarifying the literature selection process enhances the transparency and rigor of the study.

In response, we would like to emphasize that we used all relevant scientific publications available on mammal populations in the Baltic countries. Our literature search was conducted primarily via Google Scholar, using species names, country names, and relevant keywords (e.g., “mammals”, “population trends,” “distribution,” “threats,” etc. and country name). In addition to peer-reviewed articles, we also included grey literature, such as government reports, monitoring documents, national assessments, and technical publications that are often essential for capturing up-to-date or regionally specific data.

Furthermore, all three authors are actively engaged in mammal research in the Baltic region, either conducting or leading national programs. Given the limited number of national publications available for certain species, we ensured that all available and credible sources were included, regardless of their publication format. This comprehensive approach allowed us to incorporate the full scope of available knowledge on the subject.

We have now clarified this point in the revised manuscript in the section 2.2.

 

Comment: 6.Line 138. The authors mention that some data that cannot be found online were collected from official websites. I would like to know what kind of sources these official websites refer to? National libraries? Or what kind of official websites? This involves the reliability of data sources, and I hope the authors can provide a detailed explanation of this issue.

Answer: We appreciate the reviewer’s attention to the reliability of our data sources. The “official sources” referenced in Line 138 include government-published annual reports on game animal populations from the respective national environmental and forestry institutions in Lithuania, Latvia, and Estonia.

While current data (since ~2015) are available online through official portals, some earlier datasets are no longer accessible online due to the restructuring and reorganization of institutional websites. For instance, older archives were removed or replaced during updates to national environmental agency platforms or shifts in administrative responsibility. However, we would like to emphasize that these earlier data were collected directly from the same official institutions prior to their removal and are therefore equally reliable and comparable to more recent datasets. We have clarified this in the revised text to avoid any confusion about data integrity: “All game population figures, regardless of the period, originate from national programs and follow consistent data collection methodologies. The only difference is their current digital availability, not their source or validity.”

 

Comment: 7.The title of Section 2.2 is “Data Sources,” but I am not clear on what types of data the authors ultimately collected. Species distribution data? Species lists for each region? Or other types of data? Additionally, the authors analyzed changes in mammals over a 30-year period, which would require data on the structure of mammals across different years. What is the time interval between data from different periods? Five years, ten years, or something else? I suggest the author explain these issues in the paper.

Answer: We agree that further clarification of the types of data collected and the temporal structure of the dataset would improve the transparency of our methodology. We added text “Data we used in review include species distribution (coordinates or 10×10 km UTM grid cells, population numbers for game species and relative abundances for small mammals, ecological characteristics, such as habitat use, invasiveness and threats, and species status, including Red List assessments and expert evaluations”, to2.2,  and “In terms of the temporal structure of the analysis, we compared data from two main time periods: a baseline period (generally pre-2000, depending on the country and data availability) and a recent period covering 2000–2024. This results in an approximate 30-year interval. Although the exact interval varies slightly by dataset, the range allows for the analysis of long-term population trends.” To 2.3.

 

Comment: 8.I noticed that the data mentioned by the author cannot be found online, and there are no supplementary materials providing any data. This means that relying solely on the data mentioned in the paper is insufficient to reproduce the results, which significantly undermines the paper's credibility. I suggest the author carefully reconsider the way they present the data and materials.

Answer: While current data (since ~2015) are available online through official portals, some earlier datasets are no longer accessible online due to the restructuring and reorganization of institutional websites. For instance, older archives were removed or replaced during updates to national environmental agency platforms or shifts in administrative responsibility. However, we would like to emphasize that these earlier data were collected directly from the same official institutions prior to their removal and are therefore equally reliable and comparable to more recent datasets. We have clarified this in the revised text to avoid any confusion about data integrity, We also added Supplementary Table 1, which includes data on some game species. Otherwise, all data are available in references databases (which we cannot re-publish) and papers/reports/assessment.

 

Comment: 9.The article does not appear to mention appropriate statistical analysis of the data, nor does it provide detailed explanations of how the data was processed after collection. It merely mentions the use of CAGR to calculate animal populations, which does not sufficiently justify the subsequent results. It is recommended that the authors provide detailed supplementary information.

Answer: Chapters 2.2 and 2.3 were revised. We believe your comment has been addressed through these revisions. However, we would like to emphasize that no additional statistical methods were used because we do not analyze data in a review paper. CAGR was only used to compare the dynamics of species, regardless of their abundance.

 

Comment: 10.The results section of the article reads more like a “discussion” section rather than actual “results.” It is recommended that the authors refer to relevant literature on the subject and rewrite the results section accordingly.

Answer: All relevant literature sources were used for this review. We cannot rewrite the Results section by adding "relevant literature" because there are no additional references that could change the text. We understand that the format of this paper is not a strict literature review, as we use various data. However, we hope the editors will find this approach acceptable.

 

Reviewer 4 Report

Comments and Suggestions for Authors

This manuscript does a good job of updating us on the status and changes of mammal populations in the Baltic. It is well organized and written. The tables and figures are appropriate and useful. There is a thorough use of the literature, both old and recent. I only have 2 small suggestions to make: maybe spell out ASF in the abstract (line 19). And in Table 4, add the 2 citations [10, 11} to the last entry in the table as they are mentioned in the text. 

Author Response

Reviewer 4 comments and answers

Comment: This manuscript does a good job of updating us on the status and changes of mammal populations in the Baltic. It is well organized and written. The tables and figures are appropriate and useful. There is a thorough use of the literature, both old and recent. I only have 2 small suggestions to make: maybe spell out ASF in the abstract (line 19). And in Table 4, add the 2 citations [10, 11} to the last entry in the table as they are mentioned in the text. 

Answer: thank you, both comments were acknowledged in revised text.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

After reading the revised manuscript, I noticed that you have made targeted revisions to address the main issues I raised. Overall, the manuscript has been significantly improved in terms of logical structure and data interpretation. Thank you for taking my comments into consideration, and I wish you all the best in your future research.