Round 1

Reviewer 1 Report

 

This is a very detailed overview of what is known about penguin visual systems. The authors review the literature on the topic and offer their own speculations where data is missing. They often make use of information from other animal systems to supplement what is known about penguins.

 

The information within the paper is interesting and probably will be of use to someone interested in exploring the field. However, before being suitable for publication I would recommend some fairly serious editing.  I think the paper is much longer than it needs to be. This fact, combined with some awkward writing makes it more difficult to read than it needs to be. I recommend shortening in two basic ways. First, simply editing the writing to remove repetition and run-on sentences would be helpful.  Second, the use of pure speculation about aspects for which there is little or not data on penguins seemed counterproductive to me. In several places this resulted in lengthy descriptions (e.g. about habitat light, or bird visual systems) that, lacking relevant data on penguins, resulted in purely speculative statements that adding little or nothing to the current knowledge of penguins. A far better approach, in my opinion, would be to focus on those aspects of penguin vision for which there is data, and at the end summarize some of the aspects that are not known and might be interesting to investigate in the future.  In my comments below I give some examples of where too much time is devoted to material that in the end leads to no meaningful conclusions.

 

I also think the organization of the paper could be improved for clarity. I would add a short overview introduction to the topic by summarizing briefly the behavioral repertoire of penguins:  what times of day are the active, do they hunt at night, what are some the deepest known dives. It is unclear for example the extent to which some species are active at night, which is a critical consideration. Then I would present the most interesting and compelling questions. On top of the list is the fact that the eye must function in both air and water. Then in the detail sections they can address what sorts of adaptations follow from this. I  I would also combine the discussion of the anatomy of the eye with the section on optics. They go together naturally. You describe, for example, the dimensions of the eye but only much later do you discuss how this impacts visual processing. Why not put them together, and focus on how the optics and anatomy relate to the unique problems of being effective in air and water.

 

A few additional general comments:

 

1. The authors make frequent use of long run-on sentences, and use semi-colons to string together what should be separate sentences. This makes reading the manuscript challenging. In my comments below I point out several examples, but I would recommend a careful editing of the entire manuscript for readability.

 

2. The authors clearly state up front that some information they provide is their own speculation, and they indicate that they state when this is the case. However, they, in fact, often do not state when they are speculating, and in some cases the basis or logic of their speculation is unclear or unsatisfactorily stated. In my opinion it is fine to report anecdotal information or unpublished data. Pure speculation without any basis in data does not seem useful, and can be quite misleading. Some of this speculation extends beyond penguins to descriptions of other animals. In these cases, there is usually good information in other sources which in some cases contradicts what is presented here. Examples of this (see below) are the estimate of absolute visual sensitivity and the discussion of temporal responses of the eye.

 

SPECIFIC COMMENTS

 

Line 26. Are penguins active at night, or only during the day? This is a very relevant question, since it governs the range of light intensity in which they must typically operate.

 

Line 32. Luminance is a photometric unit that measure human-percieved intensity. Here it would be better to refer to a “low intensity” environment, since that objectively describes the environment.

     I don’t see the point of discussing other birds from low intensity environment. First, you have not clearly stated if (or why) penguins primarily operate in such environments. The birds you discuss are behaviorally and evolutionarily very different from penguins and it is not clear if, or why, they represent a good model for comparison. I would delete lines 32-46.

 

Line  46-54.  This is a long run-on sentence. It should be split into at least 3 different sentences for readability.

 

Line 70.  “….the light conditions under which they operate.”

 

Lines 86-87. “…attenuation of light underwater. In this regard the articles….”

 

Line 97-98.  “…of speculating or drawing our own conclusion.  We have….”

 

Line 110. “…vision is generally the most important sensory mode utilized, and this is likely to be the case for penguins.”

 

Line 111-112. “Given that they forage….”

 

Line 112-113. “We must first examine the availability of light in that environment.”  (delete the rest of the sentence).

 

Line 114-125. Do all the relevant papers use the photometric units (lux, luminance, illuminance etc.)? This is unfortunately since these are measures of human perception. Quantal units (radiance, irradiance etc.) are more appropriate. The book “Visual Ecology” by, Cronin et al. gives intensities in various aquatic habitats in quantal units.

 

Line 122-130. I’m not sure of the point of this argument. It is known that there are animals (including birds) that can detect light intensities as low as single photons striking photoreceptors, and many animals can function effectively in very intense light. It is obvious that penguin absolute sensitivity must lie somewhere between these extremes.  There is no real useful information here about penguins. This provides no basis for estimating the limits of penguin visual sensitivity. I would leave this out.

 

Line 131-141. I do not see the point of this paragraph. Again, there are some animals that can see in very very dim light (including some birds) and many that can see well in very intense light. Therefore penguins must fall somewehre in the middle. Your estimate of where they sit in this continuum seems completely arbitrary. Is this useful information? The estimate given is based on no real information.

 

It makes sense to estimate light intensities at different depths at times the animals hunt, and it is reasonable to assume they can see under those conditions. The “phylogenetic comparison” offers no useful insight.

 

Line 155. It seems odd to switch from your earlier use of photometric units to the quantal unit irradiance.

 

Lines  171-173. This hypothesis has been addressed in many different species of fish, birds and other terrestrial animals. There is some evidence that fish spectral sensitivity sometimes matches water color. However for terrestrial animals, including reptiles, hymenopteran insects, birds and mammals, the spectral sensitivity is nearly the same in all.  There is no evidence that it shifts in response to habitat color. Your hypothesis may be “reasonable” but there is a great deal of data that suggests it probably is not true. The most reasonable guess would be that penguin spectral sensitivity peaks at a similar wavelength in all species and it is similar to that of other terrestrial animals.

 

Lines 182-197. I don’t really follow the point that is being made here. You can state how dark it gets in different locations, but without evidence that penguins actually catch fish in these conditions, it doesn’t tell you much about their visual sensitivity. There does not seem to be very good information here about where and when they forage, and no direct evidence is presented about their visual sensitivity. It seems like rather circular speculation with much in the way of a meaningful conclusion.

 

This entire section on visual sensitivity seems badly overwritten. You do not actually have any information on visual sensitivity in penguins, and do not present detailed information about the light intensities at which different species operate. You could replace these two pages with a statement something like:  “Emperor penguins have been recorded diving as deep 564 m, and king penguins hunt in open pelagic waters down to 300 m. Light intensities at these depths have been estimated to be as low as…….(can get this info from “Visual Ecology” or other sources.” )Assuming they utilize vision to hunt at these depths this suggests the capacity to use vision in light as dim as ………”

 

Such a statement could replace line 109-151, and gives just as much useful information. There is really no need for you to discuss light in the ocean more generally, since the topic is well covered in a number of other sources. The discussion of light in water is well beyond the scope of this paper. You have too little information on where and when penguins forage for this to be useful in this analysis.

 

Finally, in discussing habitat light it is preferable to use quantal units, rather than photometric units (lux etc.) since the latter are based on human perception. Data about ocean light in quantal units (radiance, irradiance) is available from various sources.

 

Lines 155-181. This could be removed, or summarized much more succinctly.  It is covered well in other sources and is only indirectly relevant to data you actually present on penguin vision.

 

Lines 182-207. All the useful information about sensitivity limits are presented in these two paragraphs.

 

Lines 209-241. I do not think this information shed much light on penguin vision. It is sufficient to say they evolved basic features of their vision from birds, and those aspects shared by birds represent the ancestral condition.

 

Line 302-303. This is a large oversimplification. Depending on the shape of the eye and aspects such as focal length relative to pupil size a large eye can function to increase sensitivity (e.g. owls, deep sea fishes) or, alternatively it can be designed to increase acuity. One cannot say much based only on the size of the eye. Eyes that are large to increase acuity typically have relatively small pupils, and gain acuity by enlarging the image (not by increasing the total amount of light entering the eye). Eyes that evolve for high sensitivity evolve large pupils, and typically a short focal length, which increases the light entering the eye per unit area of retina.

 

Line 324-339. Is the shape of the penguin eye more like that of an eagle or an owl? In other words does it appear to have evolved for a low f number of high sensitivity, or more towards a high f number of increased acuity.

 

Line 366. It would nice here to provide a comparison to some other birds (or possibly humans) to show that, indeed, the penguin eye has evolved to rely less on corneal curvature for image formation. 

 

Line 318. Delete “quite substantial.”

‘

Line 381-386.  Run-on sentence. Split into multiple sentences.

 

Line 389-392. Awkwardly worded run-on sentence

 

Line 400. Delete “what I shall refer to as”

 

Line 472. Replace the semi-colon with a period.

 

Line 517.  What does “oblate” mean?  I would rewrite this as:

 

The penguin lens appears to be more spherical than is found in most terrestrial vertebrates. Spherical lenses are typical of fish eyes, which, like penguins obtain no refractive power in water from the cornea.

 

Line 524. It would be useful to give some values for a typical terrestrial bird (or even human) for comparison. The numbers by themselves don’t mean much to the reader.

 

Line 527-530. This sentence is not needed. Anyone reading this paper will know what the retina is. Start with “In many vertebrates….”

 

 

Line 574. So  penguins are trichromats? If so, this should be clearly stated.

 

Line 577. The presence of UV sensitive cones does not mean the eye suffers from image loss due to chromatic aberration. The longer wavelength cones all possess oil droplets that filter out the UV light. The UV cones (like blue cones in humans) are probably not involved in detailed image formation – they simply add some color.

 

Do penguins have rods?  How common are they relative to cones?

 

Lines 616-649. This section could be greatly shortened. Most of it applies to birds in general, and possibly to penguins. A short statement about the likely roles of oil droplets in birds (and presumably penguins) suffices. This article is not about “bird vision”, but rather about penguin vision. The details described are not particular to penguins.

 

Line 650-664. This paragraph should be deleted. It is not particularly relevant for the discussion of penguin vision and much of it is probably nonsense.  For example the sentence "Thus relative to mammals that can act more quickly and instinctively….  is, as far as a I know groundless, and I note there is no citation.  Birds, in general are as intelligent as mammals, and in many ways their visual and cognitive responses are similar.  The CFF can be measured in a number of different ways yielding different answers. In general however, it is similar for animals that rely on primarily cone vision. It does seem to be faster for flying animals. It also depends on the relative stimulation of rods vs cones (rods are slower) I cannot see how this discussion adds insight into penguin vision. bearing on decision making per se.  Finally there is no information in this part of the paragraph about penguin vision. It is full of dubious speculation about bird visual processing.

 

Lines 673-696. Is there any information of behavioral spatial resolution?  Also, it would be helpful to give values for humans for comparison.

 

Line 745. Why would “temperate climes” influence f number?

 

Line 807.  I plugged the term “binocular overlap in birds” into Google scholar and found more than ten references. Is your statement true?

 

Line 846. Delete “workings and capabilities.”

 

Line 863-871.  I would delete this line. Commenting on the utility of online resources does not seem appropriate here.

 

Line 890-892. As I mentioned above, UVS (and probably SWS) photoreceptors probably contribute little to detailed spatial analysis of visual stimuli so chromatic aberration is probably not important. UV does not degrade the imaging by other photoreceptors because they block it out with oil droplet.

Author Response

Reviewer 1:

1. This is a very detailed overview of what is known about penguin visual systems. The authors review the literature on the topic and offer their own speculations where data is missing. They often make use of information from other animal systems to supplement what is known about penguins. The information within the paper is interesting and probably will be of use to someone interested in exploring the field. However, before being suitable for publication I would recommend some fairly serious editing. I think the paper is much longer than it needs to be. This fact, combined with some awkward writing makes it more difficult to read than it needs to be. I recommend shortening in two basic ways. First, simply editing the writing to remove repetition and run-on sentences would be helpful. Second, the use of pure speculation about aspects for which there is little or not data on penguins seemed counterproductive to me. In several places this resulted in lengthy descriptions (e.g. about habitat light, or bird visual systems) that, lacking relevant data on penguins, resulted in purely speculative statements that adding little or nothing to the current knowledge of penguins. A far better approach, in my opinion, would be to focus on those aspects of penguin vision for which there is data, and at the end summarize some of the aspects that are not known and might be interesting to investigate in the future.  In my comments below I give some examples of where too much time is devoted to material that in the end leads to no meaningful conclusions.

Response: We would like to thank the reviewer for this comment and pointing out all instances where the manuscript can be improved. We agree with their suggestions. We have therefore substantially edited the manuscript and attempted to remove data that does not pertain to penguins or is pure speculation, and rearranged the paper as suggested. Please see the tracked changes in the manuscript and responses to the specific points below. Please note that the lines the reviewer referred to are no longer correct, as we have substantially shortened the text.

 

2. I also think the organization of the paper could be improved for clarity. I would add a short overview introduction to the topic by summarizing briefly the behavioral repertoire of penguins: what times of day are the active, do they hunt at night, what are some the deepest known dives. It is unclear for example the extent to which some species are active at night, which is a critical consideration. Then I would present the most interesting and compelling questions. On top of the list is the fact that the eye must function in both air and water. Then in the detail sections they can address what sorts of adaptations follow from this. I  I would also combine the discussion of the anatomy of the eye with the section on optics. They go together naturally. You describe, for example, the dimensions of the eye but only much later do you discuss how this impacts visual processing. Why not put them together, and focus on how the optics and anatomy relate to the unique problems of being effective in air and water.

Response: We have now in the introduction examined the behavioural repertoire of penguins (sections 1.1 - 1.4), stated those compelling questions in the introduction and also combined the anatomy of the eye with the optics (sections 3.1.1 - 3.1.4).

 

A few additional general comments:

1. The authors make frequent use of long run-on sentences, and use semi-colons to string together what should be separate sentences. This makes reading the manuscript challenging. In my comments below I point out several examples, but I would recommend a careful editing of the entire manuscript for readability.

Response: We have re-edited to simplify sentence structure throughout the manuscript.

 

2. The authors clearly state up front that some information they provide is their own speculation, and they indicate that they state when this is the case. However, they, in fact, often do not state when they are speculating, and in some cases the basis or logic of their speculation is unclear or unsatisfactorily stated. In my opinion it is fine to report anecdotal information or unpublished data. Pure speculation without any basis in data does not seem useful, and can be quite misleading. Some of this speculation extends beyond penguins to descriptions of other animals. In these cases, there is usually good information in other sources which in some cases contradicts what is presented here. Examples of this (see below) are the estimate of absolute visual sensitivity and the discussion of temporal responses of the eye.

Response: We have, we hope, eliminated speculation by extensive editing and deleting as per the specific comments below and have eliminated most of the references to other animals, except where they seem very relevant, which in some cases is requested by the reviewers (e.g. a shape comparison of the globe and comparison of the corneal curvature)

 

SPECIFIC COMMENTS

1. Line 26. Are penguins active at night, or only during the day? This is a very relevant question, since it governs the range of light intensity in which they must typically operate.

Response: We have included in the introduction a section on penguin behaviour (section 1.3) and the depths to which they dive.

 

2. Line 32. Luminance is a photometric unit that measure human-percieved intensity. Here it would be better to refer to a “low intensity” environment, since that objectively describes the environment.

Response: The section now included in 1.3, has been edited to use the terms ‘low intensity’ or ‘dim’ and photometric units have been removed entirely

 

3. I don’t see the point of discussing other birds from low intensity environment. First, you have not clearly stated if (or why) penguins primarily operate in such environments. The birds you discuss are behaviorally and evolutionarily very different from penguins and it is not clear if, or why, they represent a good model for comparison. I would delete lines 32-46.

Response: The section (the last paragraph of section 1. Introduction) has been deleted as suggested.

 

4. Line 46-54.  This is a long run-on sentence. It should be split into at least 3 different sentences for readability.

Response: This sentence is in a part of the paper that has been extensively rewritten

 

5. Line 70. “….the light conditions under which they operate.”

Response: The section 1.4, originally containing this sentence, has been extensively rewritten for clarity.

 

6. Lines 86-87. “…attenuation of light underwater. In this regard the articles….”

Response: The first paragraph of section 2, originally containing this sentence, has been extensively modified for clarity.

 

7. Line 97-98. “…of speculating or drawing our own conclusion.  We have….”

Response: This sentence has been deleted from the second paragraph of section 2.

 

8. Line 110. “…vision is generally the most important sensory mode utilized, and this is likely to be the case for penguins.”

Response: We have attempted to justify this in the first paragraph of the introduction, as clearly this whole discussion is irrelevant if vision is not a useful sense for penguins

 

9. Line 111-112. “Given that they forage….”

Response: Edited and changed per reviewer’s suggestion.

 

10. Line 112-113. “We must first examine the availability of light in that environment.” (delete the rest of the sentence).

Response: Most of this section has been extensively rewritten.

 

11. Line 114-125. Do all the relevant papers use the photometric units (lux, luminance, illuminance etc.)? This is unfortunately since these are measures of human perception. Quantal units (radiance, irradiance etc.) are more appropriate. The book “Visual Ecology” by, Cronin et al. gives intensities in various aquatic habitats in quantal units.

Response: Thank you – Cronin is very valuable and we have eliminated photometric units and now use cdm^-2. It was difficult in one part as one author used photometric units but in a later publication, with a similar diagram, he converted these to quantal units (lines 79-95). We have also shortened the discussion on light attenuation underwater greatly.

 

12. Line 122-130. I’m not sure of the point of this argument. It is known that there are animals (including birds) that can detect light intensities as low as single photons striking photoreceptors, and many animals can function effectively in very intense light. It is obvious that penguin absolute sensitivity must lie somewhere between these extremes. There is no real useful information here about This provides no basis for estimating the limits of penguin visual sensitivity. I would leave this out.

Response: The sentence has been deleted

 

13. Line 131-141. I do not see the point of this paragraph. Again, there are some animals that can see in very very dim light (including some birds) and many that can see well in very intense light. Therefore penguins must fall somewehre in the middle. Your estimate of where they sit in this continuum seems completely arbitrary. Is this useful information? The estimate given is based on no real information.

Response: This paragraph has been deleted.

 

14. It makes sense to estimate light intensities at different depths at times the animals hunt, and it is reasonable to assume they can see under those conditions. The “phylogenetic comparison” offers no useful insight.

Response: This section has been deleted as suggested.

 

15. Line 155. It seems odd to switch from your earlier use of photometric units to the quantal unit irradiance.

Response: We have deleted much of this section and used quantal units where relevant.

 

16. Lines 171-173. This hypothesis has been addressed in many different species of fish, birds and other terrestrial animals. There is some evidence that fish spectral sensitivity sometimes matches water color. However for terrestrial animals, including reptiles, hymenopteran insects, birds and mammals, the spectral sensitivity is nearly the same in all.  There is no evidence that it shifts in response to habitat color. Your hypothesis may be “reasonable” but there is a great deal of data that suggests it probably is not true. The most reasonable guess would be that penguin spectral sensitivity peaks at a similar wavelength in all species and it is similar to that of other terrestrial animals.

Response: This section has been deleted. However, in 3.1.9 line 508 we do note that the spectral sensitivity of Humboldt penguin opsins has been measured and it has been found that there is a shift in the LWS sensitivity.

 

17. Lines 182-197. I don’t really follow the point that is being made here. You can state how dark it gets in different locations, but without evidence that penguins actually catch fish in these conditions, it doesn’t tell you much about their visual sensitivity. There does not seem to be very good information here about where and when they forage, and no direct evidence is presented about their visual sensitivity. It seems like rather circular speculation with much in the way of a meaningful conclusion.

This entire section on visual sensitivity seems badly overwritten. You do not actually have any information on visual sensitivity in penguins, and do not present detailed information about the light intensities at which different species operate. You could replace these two pages with a statement something like:  “Emperor penguins have been recorded diving as deep 564 m, and king penguins hunt in open pelagic waters down to 300 m. Light intensities at these depths have been estimated to be as low as…….(can get this info from “Visual Ecology” or other sources.” )Assuming they utilize vision to hunt at these depths this suggests the capacity to use vision in light as dim as ………”

Response: We have deleted this section entirely and included parts of it in the introduction 1.3 where relevant to the behaviour of different penguin species

 

18. Such a statement could replace line 109-151, and gives just as much useful information. There is really no need for you to discuss light in the ocean more generally, since the topic is well covered in a number of other sources. The discussion of light in water is well beyond the scope of this paper. You have too little information on where and when penguins forage for this to be useful in this analysis.

Response: We have now put this information in to the introduction.

 

19. Finally, in discussing habitat light it is preferable to use quantal units, rather than photometric units (lux etc.) since the latter are based on human perception. Data about ocean light in quantal units (radiance, irradiance) is available from various sources.

Response: We have extensively rewritten this section.

 

20. Lines 155-181. This could be removed, or summarized much more succinctly. It is covered well in other sources and is only indirectly relevant to data you actually present on penguin vision.

Response: These lines have now been deleted.

 

21. Lines 182-207. All the useful information about sensitivity limits are presented in these two paragraphs.

Response: These two paragraphs have been kept, in 1.3

 

22. Lines 209-241. I do not think this information shed much light on penguin vision. It is sufficient to say they evolved basic features of their vision from birds, and those aspects shared by birds represent the ancestral condition.

Response: We have deleted these paragraphs and replaced them as suggested.

 

23. Line 302-303. This is a large oversimplification. Depending on the shape of the eye and aspects such as focal length relative to pupil size a large eye can function to increase sensitivity (e.g. owls, deep sea fishes) or, alternatively it can be designed to increase acuity. One cannot say much based only on the size of the eye. Eyes that are large to increase acuity typically have relatively small pupils, and gain acuity by enlarging the image (not by increasing the total amount of light entering the eye). Eyes that evolve for high sensitivity evolve large pupils, and typically a short focal length, which increases the light entering the eye per unit area of retina.

Response: Deleted; we have explained the f-number in 3.1.4.

 

24. Line 324-339. Is the shape of the penguin eye more like that of an eagle or an owl? In other words does it appear to have evolved for a low f number of high sensitivity, or more towards a high f number of increased acuity.

Response: We have explained the shape of both eagle and owl eyes but noted that the penguin eye has a more simple shape (3.1.3) and then in another section looked at the f-number, which varies between penguin species.

 

25. Line 366. It would nice here to provide a comparison to some other birds (or possibly humans) to show that, indeed, the penguin eye has evolved to rely less on corneal curvature for image formation.

Response: The section 3.1.5 (lines 333-339) has been modified to include a comparison to other birds.

 

26. Line 318. Delete “quite substantial.”

Response: The phrase has been deleted.

 

27. Line 381-386. Run-on sentence. Split into multiple sentences.

Response:  The sentence has been split.

 

28. Line 389-392. Awkwardly worded run-on sentence

Response: The sentence has been altered.

 

29. Line 400. Delete “what I shall refer to as”

Response: The phrase has been deleted.

 

30. Line 472. Replace the semi-colon with a period.

Response: The semi-colon has been replaced with a period.

 

Line 517.  What does “oblate” mean?  I would rewrite this as:

The penguin lens appears to be more spherical than is found in most terrestrial vertebrates. Spherical lenses are typical of fish eyes, which, like penguins obtain no refractive power in water from the cornea.

Response: The sentence has been rewritten as suggested.

 

31. Line 524. It would be useful to give some values for a typical terrestrial bird (or even human) for comparison. The numbers by themselves don’t mean much to the reader.

Response: Values for human have been provided for comparison (lines 468-470).

 

32. Line 527-530. This sentence is not needed. Anyone reading this paper will know what the retina is. Start with “In many vertebrates….”

Response: The sentence has been deleted as suggested.

 

33. Line 574. So penguins are trichromats? If so, this should be clearly stated.

Response: The trichromatic status of penguins has now been stated in section 3.1.9 line 506

 

34. Line 577. The presence of UV sensitive cones does not mean the eye suffers from image loss due to chromatic aberration. The longer wavelength cones all possess oil droplets that filter out the UV light. The UV cones (like blue cones in humans) are probably not involved in detailed image formation – they simply add some color.

Response: This reference has been deleted.

 

35. Do penguins have rods? How common are they relative to cones?

Response: We have put in some information

 

36. Lines 616-649. This section could be greatly shortened. Most of it applies to birds in general, and possibly to penguins. A short statement about the likely roles of oil droplets in birds (and presumably penguins) suffices. This article is not about “bird vision”, but rather about penguin vision. The details described are not particular to penguins.

Response: The section has been shortened as suggested.

 

37. Line 650-664. This paragraph should be deleted. It is not particularly relevant for the discussion of penguin vision and much of it is probably nonsense. For example the sentence "Thus relative to mammals that can act more quickly and instinctively….  is, as far as a I know groundless, and I note there is no citation.  Birds, in general are as intelligent as mammals, and in many ways their visual and cognitive responses are similar.  The CFF can be measured in a number of different ways yielding different answers. In general however, it is similar for animals that rely on primarily cone vision. It does seem to be faster for flying animals. It also depends on the relative stimulation of rods vs cones (rods are slower) I cannot see how this discussion adds insight into penguin vision. bearing on decision making per se.  Finally there is no information in this part of the paragraph about penguin vision. It is full of dubious speculation about bird visual processing.

Response: This paragraph has been deleted.

 

38. Lines 673-696. Is there any information of behavioral spatial resolution? Also, it would be helpful to give values for humans for comparison.

Response: We have referenced a preliminary experiment that we presented as a poster (line 594) and have included human values also (line 597) now

 

39. Line 745. Why would “temperate climes” influence f number?

Response: We have deleted this. What we were implying (but didn’t explain) in the original manuscript was the increased illumination with a higher sun than in higher latitudes.

 

40. Line 807. I plugged the term “binocular overlap in birds” into Google scholar and found more than ten references. Is your statement true?

Response: We have changed this around in section 3.3.4 to really say that what is not known is whether birds including penguins have true stereopsis; of course they can use both eyes together and most have a binocular field. We did not express this clearly.

 

41. Line 846. Delete “workings and capabilities.”

Response: The phrase has been deleted.

 

42. Line 863-871. I would delete this line. Commenting on the utility of online resources does not seem appropriate here.

Response: This has now been deleted

 

43. Line 890-892. As I mentioned above, UVS (and probably SWS) photoreceptors probably contribute little to detailed spatial analysis of visual stimuli so chromatic aberration is probably not important. UV does not degrade the imaging by other photoreceptors because they block it out with oil droplet.

Response: The sentence has been deleted.

Reviewer 2 Report

The title of this manuscript is not suited according to the study results, it should be changed

Abstract

Introduction of the subject experiment not given and explained. Author should explain briefly why this study required to conduct? Results presentations not in scientific terms, it should need to revise profoundly. Future directions are also not presented well overloaded text should need to removed.

Keywords. This sections also should need to revisit according scientific requirement

1.      Introduction/Background

 

2.       The overall introduction/background section is very confusing and it needs major revision as the authors have added a lot of irrelevant information. This section should be precise and to the point. Most of the literature is much old irrelevant to the experiment which needs to be addressed.

1.      There is several overlapping information in this section, authors are advised to remove such information.

2.      Remove all outdated references and keep the latest.

3.      Overall need more explanation and background in this section

4.      A lot of grammar errors in this section, should need to revise again

5.      References used in the introduction section are too old

Material and Methods 

very confusing and not clear, should need to revist

Results

1.      There is no significance shown in all tables 2, data was not interpreted properly 

2.      Results are described without heading, make sub-headings and describe information under those sub-headings.

3.      Result presentation is very rough, should need to rewrite

Discussion

1.      The discussion need to be revised and need to make it more focused based on results.

2.      Remove the overlapping information/statements.

3.      Interpretation was not justifiable

4.      Irrelevent and extra data need to removed

References

 

1.      Update the reference section with latest findings keep only those old reference which are utmost important. 

Author Response

Reviewer 2:

1. The title of this manuscript is not suited according to the study results, it should be changed

Response: Thank you for the comment. We have heavily edited the manuscript and hope the title is now reflective of the paper.

 

2. Abstract

Introduction of the subject experiment not given and explained. Author should explain briefly why this study required to conduct? Results presentations not in scientific terms, it should need to revise profoundly. Future directions are also not presented well overloaded text should need to removed.

Response: We have edited the abstract substantially.

 

3. Keywords. This sections also should need to revisit according scientific requirement

Response: We have now put in between 3 to 10 keywords, as instructed, using words that are not in the title of the of the manuscript as they will be picked up by a search regardless.

 

4. Introduction/Background

The overall introduction/background section is very confusing and it needs major revision as the authors have added a lot of irrelevant information. This section should be precise and to the point. Most of the literature is much old irrelevant to the experiment which needs to be addressed.

Response: We have extensively revised this, deleting a lot of information that does not relate to other birds but including, as requested by review 1, information on penguin behaviour that relates to vision.

 

1. There is several overlapping information in this section, authors are advised to remove such information.

Response:

 

2. Remove all outdated references and keep the latest.

Response: Outdated references have been removed as suggested; there are still a few old ones that we think are important (e.g. Matthiessen and Wood), as we in the methods state that we are looking at all papers published concerning penguins, but 33 have been deleted.

 

3. Overall need more explanation and background in this section

Response: We have included more information about penguin vision and different species in 1.3

 

4. A lot of grammar errors in this section, should need to revise again

Response: We have revised this and performed a careful spelling and grammar check; PWH is a native English speaker but we have also asked other native English speakers to read the text. Many of the sentences were too long and difficult to follow we agree.

 

5. References used in the introduction section are too old

Response: We have deleted irrelevant older references

 

Material and Methods: very confusing and not clear, should need to revisit

 

1. ResultsThere is no significance shown in all tables 2, data was not interpreted properly

Response: We are unsure about this as there is no table 2. For table 1, we just took the available data and put it in our table; we were not trying to interpret it further than this, merely just show what others had reported.

 

2. Results are described without heading, make sub-headings and describe information under those sub-headings.

Response: We have put sub-headings in.

 

3. Result presentation is very rough, should need to rewrite

Response: We have reconfigured the results and removed the part about underwater illumination, the relevant bits of which we have included under penguin behaviour

 

Discussion

1. The discussion need to be revised and need to make it more focused based on results.

Response: We have extensively revised the discussion

 

Remove the overlapping information/statements.

Response: We have done this – we had done this multiple times

 

 Interpretation was not justifiable

We have completely revised the discussion and focussed on the core questions as well as what remains unanswered

 

. Irrelevent and extra data need to removed

 

References

1. Update the reference section with latest findings keep only those old reference which are utmost important.

Response: We have deleted 33 references; we have kept some old references where we think they add information that has not been superseded or that is still referred to (e.g. Walls and his outdated description of penguins being notoriously myopic in air)

 

 

 

Reviewer 3 Report

this manuscript is an overview about penguin visual system, I think it is interesting and fitted for Vision, I just hope the authours can cite some references in manuscript(see the attached Pdf).

Comments for author File: Comments.pdf

Author Response

Reviewer 3:

this manuscript is an overview about penguin visual system, I think it is interesting and fitted for Vision, I just hope the authours can cite some references in manuscript(see the attached Pdf).

Response: we have changed the abstract as requested. The other two areas that references were asked to be inserted into have now been extensively revised as per other reviewers’ comments, but we have added references at equivalent places (e.g. line 719 and 734).

Round 2

Reviewer 1 Report

The revision has, in my view, greatly improved the readability and clarity of the manuscript. I have only a few very minor suggestions/comments.

 

line 38.  "...probably represent the ancestral condition..."

 

line 139-140. The sentence "These questions themselves beget a third...." should be deleted. It seems repetitive.

 

line 274. The focal length is, I believe, the distance from the nodal point to the retina (rather     than the axial length).

 

line 333 I would delete the word "Furthermore,"

 

line 434. It would be useful to mention what methods were used in this study. Were they similar to the earlier studies, or were more reliable more modern techniques applied?

 

line 460-462. The spherical shape of fish lenses make them very powerful. However, Fish lenses accommodation involves movement of the lens itself, rather than changing its shape -- which is presumably difficult with a spherical lens. Do the authors have any thoughts on how penguins could use a more spherical lens and still be able to accommodate effectively? Is there any evidence they can move the lens?

Author Response

line 38.  "...probably represent the ancestral condition..."

Response

Probably has been inserted

 

line 139-140. The sentence "These questions themselves beget a third...." should be deleted. It seems repetitive.

Response

This has been deleted

 

line 274. The focal length is, I believe, the distance from the nodal point to the retina (rather     than the axial length).

Response

Yes this was unclear. Further, we had already stated that the focal length is part of the formula to calculate the f-number. Therefore we have deleted this and just discussed the entrance pupil.

 

line 333 I would delete the word "Furthermore,"

Response

This has been deleted

 

line 434. It would be useful to mention what methods were used in this study. Were they similar to the earlier studies, or were more reliable more modern techniques applied?

Response

We have inserted ‘also using retinoscopy’, which was the same (also stated) as used in the older studies, along with photorefraction.

 

line 460-462. The spherical shape of fish lenses make them very powerful. However, Fish lenses accommodation involves movement of the lens itself, rather than changing its shape -- which is presumably difficult with a spherical lens. Do the authors have any thoughts on how penguins could use a more spherical lens and still be able to accommodate effectively? Is there any evidence they can move the lens?

Response

Yes further examination of the penguin lens is likely to be very rewarding. We have expanded on this paragraph to note that no one has looked for lens movement in the penguin. As you say, a more spherical lens will reduce the accommodative potential of a change in lens shape and we have noted this. We also have noted that the eye may be in a slightly accommodated state when enucleated, which might mean that it is not always as spherical as has been measured, as all such measurements have been done post-mortem.

Reviewer 2 Report

I am satisfied with the revision made by the authors 

Author Response

Thank you