Reproductive Success of Tree Swallows at Abandoned Mine Drainage Treatment Ponds

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript entitled "Reproductive Success of Tree Swallows at Abandoned Mine Drainage Treatment Ponds" scientifically evaluated whether the distance between the ponds and the nests affected various reproductive parameters. The author conducted a field experiment using the tree swallows as models. The results were interesting and of value, suggesting that individuals closer to the pond have a higher reproductive success. Despite this, some parts of the manuscript need to be improved. Hope the below comments will be able to help to further improve this work.

 

Abstract

Lines 21-25 There are some problems with the first two sentences of the abstract; you should start by writing about the background of the study and the existing scientific problem. Then lead into your specific object of study.

 

Introduction

Lines 38-45 Same problem here. The beginning of the introduction needs to introduce the reader to the background of the study, not directly to the subject of your study. The characteristics of the tree swallow you mention should be used appropriately by you to solve a scientific problem. You could start by asking a question about animal-environment interactions, and then say what kind of characteristics the tree swallows have, and therefore can be used as a model to study that question. This is because your readers will not just be people concerned with tree swallows, but other environmentally related researchers will also be interested in your study, and the opening paragraph as it stands could give the false impression that you are only specialising in tree swallows' behaviour.

Lines 78-82 These details can be put into the study methods section.

 

Materials and Methods

Lines 98-99 These numbers don't seem to have much to do with the study.

Line 107 Does this lake interfere with the study? Because these birds can also visit this lake to feed. Also, where is the main source of water for the birds in the FAR group? Is it also these waters on the north side of the map? But as described in the first paragraph of your introduction, it doesn't seem to be.

Lines 123-128 Why are you only measuring these mineral-related parameters? Other common water quality parameters are also informative, such as Chemical Oxygen Demand, Total Dissolved Solids, Heavy Metals such as Cd, Ammonia Nitrogen, Bacteria, etc.

Lines 175-177 I think there is a problem here. You started by saying that these birds would forage at a range of 400 metres. Therefore, you are wrong to combine this middle group with the FAR group. And there is a clear clustering of the three sets of nest boxes as seen on the map. I think the data processing should retain the three scales set at the beginning.

 

Results

Lines 214-215 The clarity of the figure is very low.

Lines 254-255 The nestlings in the NEAR group don't look like they are gaining weight, and this graph confuses me. In addition, since Figures 3 and 4 have fitted lines, you need to provide R².

 

Discussion

Lines 301 One issue that the study may have overlooked is the health of the nestlings. Breeding data looks better in the NEAR group, but are the nestlings healthier? Maybe in future studies, you can measure some physiological data. Nestlings in the NEAR group may have easier access to food and therefore grow faster. But in fact, their bodies may have been enriched with harmful substances.

 

Reference

Current reference formats are not consistent.

Comments on the Quality of English Language

Minor editing of English language required.

Author Response

Thank you for your review. Your comments have definitely improved my work. I will respond to your comments point-by-point:

• Abstract. Lines 21-25 There are some problems with the first two sentences of the abstract; you should start by writing about the background of the study and the existing scientific problem. Then lead into your specific object of study.

I agree and revised accordingly.

• Introduction. Lines 38-45 Same problem here. The beginning of the introduction needs to introduce the reader to the background of the study, not directly to the subject of your study. The characteristics of the tree swallow you mention should be used appropriately by you to solve a scientific problem. You could start by asking a question about animal-environment interactions, and then say what kind of characteristics the tree swallows have, and therefore can be used as a model to study that question. This is because your readers will not just be people concerned with tree swallows, but other environmentally related researchers will also be interested in your study, and the opening paragraph as it stands could give the false impression that you are only specialising in tree swallows' behaviour.

I simply re-ordered my paragraphs and start with a discussion of abandoned mine drainage and how it can affect ecosystems. I do not mention Tree Swallows now until the fifth paragraph.

• Lines 78-82 These details can be put into the study methods section.

I kept the definition of "bird productivity" here. I felt it was import to list the various ways it can be measured. It was also important for the reader to know the importance of egg lay date and how it corresponds in other studies to higher reproductive success. This discussion is best kept in the Introduction.

1. Materials and Methods. Lines 98-99 These numbers don't seem to have much to do with the study.

I agree with you. However, the last time I submitted a manuscript to Birds, the editor asked me to insert this information, implying it was policy for all papers to contain this information--reasoning that it helps international readers understand the study site better. Therefore in this submission I elected to keep it on the chance that the current editor would request it be added back in.

• Line 107 Does this lake interfere with the study? Because these birds can also visit this lake to feed. Also, where is the main source of water for the birds in the FAR group? Is it also these waters on the north side of the map? But as described in the first paragraph of your introduction, it doesn't seem to be.

Good point about the lake. Interestingly, the Tree Swallows almost never forage over the lake. I conducted point-counts for a separate (unpublished) study at the same time as I was doing this Tree Swallow work. Only one Tree Swallow was recorded out of 429 observations. I inserted this information on Lines 120-121  and in footnote 27. The FAR group of nest boxes is not near any permanent surface water, but there are small wetland areas along edges of most agricultural fields. The soil is wet enough to support growth of cattails, so I assume aquatic insect larvae may live there, but I do not know. I discussed this on Lines 113-117.

• Lines 123-128 Why are you only measuring these mineral-related parameters? Other common water quality parameters are also informative, such as Chemical Oxygen Demand, Total Dissolved Solids, Heavy Metals such as Cd, Ammonia Nitrogen, Bacteria, etc.

I had other data and inserted it per your request. I did not have information on bacteria, COD, or ammonia nitrogen.

• Lines 175-177 I think there is a problem here. You started by saying that these birds would forage at a range of 400 metres. Therefore, you are wrong to combine this middle group with the FAR group. And there is a clear clustering of the three sets of nest boxes as seen on the map. I think the data processing should retain the three scales set at the beginning.

This ended up being the most important criticism of my work, because despite my originally saying that the MID group was most similar to the FAR group, now that I have analyzed the groups separately, it appears the MID group is more similar to the NEAR group. In any case, the MID group almost always had intermediate values between the NEAR and FAR groups, and that's a pretty interesting finding. I was reluctant to try this because I was worried about losing statistical power. I did to some degree, and given how few nests were in the MID group, those data are not the most conclusive. Still, I thank you for asking me to do the right thing. You will see my data analysis has been completely re-done to account for three groups instead of two.

• Results. Lines 214-215 The clarity of the figure is very low.

I had to re-do the figure anyway, so I think you'll find it's better now.

• Lines 254-255 The nestlings in the NEAR group don't look like they are gaining weight, and this graph confuses me. In addition, since Figures 3 and 4 have fitted lines, you need to provide R².

I provided R2 values in the caption of the Figure. You will find that the NEAR group's regression line is flat and the R2 is near zero. This is because the data are too thin at the younger and older nestling ages to draw a line with any kind of confidence (see Lines 347-350). I re-did the analysis to account for three distance groups and there is no significant interaction term, so please concentrate on the overall increasing function (significant) rather than the three individual groups. In fact, as I type this, I am wondering if I should just remove the three regression lines and just plot one.

• Discussion. Lines 301 One issue that the study may have overlooked is the health of the nestlings. Breeding data looks better in the NEAR group, but are the nestlings healthier? Maybe in future studies, you can measure some physiological data. Nestlings in the NEAR group may have easier access to food and therefore grow faster. But in fact, their bodies may have been enriched with harmful substances.

I inserted this idea into Lines 364-368.

• Reference. Current reference formats are not consistent.

I reviewed each one and found one or two errors, but I didn't see any big discrepancies.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors present a study on the reproductive success of Tree Swallows at abandoned mine drainage treatment ponds! This study sheds light on the possible impact of treatment ponds on the breeding outcomes of these birds. The study addresses a specific and relevant research question and was conducted following established protocols for monitoring bird nests and collecting morphological data, and the analyses are appropriate. The paper is well written and flows well, but I found several points that I consider important and should be addressed by the authors:  

Abstract: Reword 2^nd sentence. It insinuates that swallows feed directly from the pond during the larval stages, while you suggest that this influences their adult populations, which are prey for the swallows.

Line 141 – Please justify, or give a reference, as to why all boxes faced East.

Line 152 – you measured randomly a single nestling in each nest. How was it chosen? Why? Is hatching synchronous? Did this bring in a bias?

Lines 156-160 – Why not simply take the date between visits – as recommended by the Mayfield method?

Lines 170-171 – if you monitored the nests every 3-4 days, how were some nestlings too old to measure? Did you not measure according to the hatching dates? Please clarify in the text.

Lines 203 – 204 – “…… the number of young that hatched and survived long enough to be counted …….” - Did you not monitor all nests throughout the breeding season? The sentence insinuates that the study was conducted with fixed dates without necessarily considering the species' breeding biology.

Lines 264-265 – “Our rationale was that water contamination at the ponds would negatively impact the 264 quality or quantity of food fed to nestlings…” This suggests that the swallows are collecting prey directly from the pond. Hence, please clarify that these are aerial foragers and that your true intention is that the adults are contaminated, assuming they have emerged from the ponds.

Lines 282-83 – could you explain/justify why data was not collected at 6 days of age?

 

Line 331 – Please give Latin names of organisms when first mentioned.

Author Response

Thank you for reviewing my paper. Your comments have improved my work. I will respond to each point in turn:

• Abstract: Reword 2^nd sentence. It insinuates that swallows feed directly from the pond during the larval stages, while you suggest that this influences their adult populations, which are prey for the swallows.

I tried to make this sentence more clear. See Lines 22-24.

• Line 141 – Please justify, or give a reference, as to why all boxes faced East.

Done. See Lines 165-166.

• Line 152 – you measured randomly a single nestling in each nest. How was it chosen? Why? Is hatching synchronous? Did this bring in a bias?

The morphological measurements were taken on a single nestling, but the nestling mass is the average of the brood (Lines 176-177). I chose the nestling from the brood based on its average appearance. I avoided the largest and the smallest (Lines 179-180). There is asynchronous hatching, and this does result in small differences in size among the nestlings, though I often could not tell just from looking at them. I considered whether my near-random selection of a single nestling could introduce bias in my results. The answer is no, but it could introduce extra statistical noise in just one case: the comparison of wing chord to nestling age. In this case, the wing chord is exactly what I measured the nestling to be, so that number is accurate. However, the age could be a little less than shown if I happened to choose one of the later-hatching nestlings (Lines 195-198).

• Lines 156-160 – Why not simply take the date between visits – as recommended by the Mayfield method?

I had not heard of the Mayfield method so I looked it up. It is a technique used in the calculation of nest survival rates. That's not really what I'm doing here, so I think it's apples-and-oranges. In any case, my technique of using published species averages for incubation and nestling periods has some inprecision, but so does the Mayfield method, and it's impossible to know if one would be any better than the other. Therefore, I stuck with my original method. If it's any comfort, I always reviewed the nest visit records after the young fledged to make sure that my estimates were consistent with the visit records.

• Lines 170-171 – if you monitored the nests every 3-4 days, how were some nestlings too old to measure? Did you not measure according to the hatching dates? Please clarify in the text.

**First, nest visit occurred every 2 and 3 days, not 3 and 4. However, I understand that's not your main concern. My main problem was I wanted to both band the nestlings and measure them on the same day (Lines 184-187). That minimizes disturbance and stress for the parents, who defensively zoom over our heads during the time we are handling the nestlings. As I explain now in the text, I had a limited window of time when I could band the nestlings, and I had trouble scheduling all the required nest visits into that window. I knew I had a problem in 2022 with this, so I became less restrictive with the ages at which I took measurements. I say this a little better on Lines 207-211.

• Lines 203 – 204 – “…… the number of young that hatched and survived long enough to be counted …….” - Did you not monitor all nests throughout the breeding season? The sentence insinuates that the study was conducted with fixed dates without necessarily considering the species' breeding biology.

I understand how this was confusing. By "survived long enough to be counted" I just meant that I did not always visit a nest on the day after hatching, so there could have been a nestling that hatched but then died and was discarded by its parents. As I edited the manuscript to address other issues, this whole sentence was deleted.

• Lines 264-265 – “Our rationale was that water contamination at the ponds would negatively impact the 264 quality or quantity of food fed to nestlings…” This suggests that the swallows are collecting prey directly from the pond. Hence, please clarify that these are aerial foragers and that your true intention is that the adults are contaminated, assuming they have emerged from the ponds.

Line 327 contains an edit that should clarify this.

• Lines 282-83 – could you explain/justify why data was not collected at 6 days of age?

See my explanation above (noted by the **).

• Line 331 – Please give Latin names of organisms when first mentioned.

Of course. I corrected this.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have appropriately addressed the reviewers’ comments. According to the current version, I have no further comments and recommend to accept.

Comments on the Quality of English Language

Minor editing of English language required

Author Response

Thank you for reading our submission again.