Infrequent Cooperative Breeding in a Short-Lived Migratory Songbird, the Wilson’s Warbler

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Comments & Suggestions

 

 Infrequent Cooperative Breeding in a Short-Lived Migratory Songbird, the Wilson’s Warbler

 

 

 

Comments

• 130: hoeever (was omitted w)
• 134-137: Can you provide other arguments/details regarding the uniqueness of this species' behavior (citation of reference papers, monographs of the species, etc.)?
• Figure1: It might be relevant to use photos that capture the described behaviour of this species. Did you use photo traps for this study?
• 150: A more detailed explanation of the working method is needed, e.g. how the observations were made (what optical devices were used), from what positions relative to the nests, on what days, intervals, at what stages of reproductive biology, etc. It should also be explained how the specimens were captured, whether official permits were required, etc.
• 150: Could telemetry be applied for a more detailed study, especially regarding the home range and the intersection with other neighboring territories?
• 157: I based many of the findings in this study. What exactly does many mean?
• 157-158: Do you think that the observations were sufficient for just one nest? I'm thinking especially about the use of terms/definitions regarding this type of behavior. Perhaps if there were a larger number of nests under observation, the results and conclusions would have been, to a greater or lesser extent, different.
• 177-180: these explanations are rather results of the study and as such should be reviewed from this chapter. Attention also to other previous sentences, where there may be aspects related to the results and not to the methodology
• 220-222: Why didn't you use statistics to also demonstrate the significance of some results?
• 223-229: same comment as in 220-222. I think you could use various statistic tests that involve numbers, or percentages.
• 267-269: same comment as in 220-222
• 3.1. – 3.9.: In addition to the description made in the 9 subchapters, I believe that a synthesis of these data/observations was necessary, possibly as a table.
• 3.7.: same comment as in 220-222
• 341-342: The phrase should have been reformulated, evidence provided through quotes
• 342-390: At least some of the content is repeated in the results in one form or another, or should rather be included in the conclusions. Rethink and rephrase this paragraph.
• 408: ccrtain, please correct
• 435: Chaetzzra pelagica, please correct with Chaetura..
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Suggestions

  -        To admit or eliminate the degree of infrequent helping behavior as the main cause of the kinship in the present study, a genetic analysis of the participating specimens may be necessary (considering also those specified of you at 514-516).

Author Response

As an initial statement, there was a disconnect between the numbering of the sentences indicated by the reviewer, and those on the current draft that I was using.  I do not know how this problem occurred, but it made it difficult to always tell to what line on my draft the reviewer was referring.  Initially the offset in line numbers was 32 lines, but toward the end of the paper it had increased to 104 lines.  In addressing reviewer comments, I have stated the reviewers line numbers and then, (in parenthesis) those that I best interpreted them to refer to in my draft.  Addtionally, my text insertions (underlined and bold) and deletions (strikethrough) may have altered line numbering.  My responses are to the referees stated Line numbers.

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Line134-237 (166-159) – The Wison’s Warbler has many unique attriburtes, and to mention a few: Dual timing of migratory return (Gilbert 2023, Ecology and Evolution, Stewart ), non-territorial nesting, no dawn singing, and a cloacal protuberance index, indicative of sperm competition, among the largest of dozen or so of investigated worldwide species (Ammon and Gilbert, 2020).  Much of these features will be topics of future papers.   However, these unique attributes do not have direct relevance to the current study.  Infrequent cooperative breeding is not unique with WIWAs, and is shared with multiple other passerines, as noted in this paper. The main goal of this paper is to establish infrequent helping as behavior that is distinct from helping characteristic of entire species (frequent coop breeding), and to describe some unique behaviors associated with the new category of helping behavior (infrequent helping). 

Fig. 1. - A photo of the subject species might be of general interest, and thus I include one.  A photo illustrating studied behavior would be ideal, but not part of the study.  In any case, while video might show behavior, still photos would be a challenge to do do.  I have authorization to use the photo I provide, and am providing a caption.  However, I have contacted the Cornell Lab (McCaulay Library) to possibly get a replacement, since the photo included was used in a paper several years ago, and I am not certain it can be used twice.  If there are problems including a photo used previously, and if a replacement cannot be obtained in time, mention of figure  1 (the photo) can be eliminated from the text, as it does not add critical data to the manuscript.   

Line 150 (182) – I have revised text to state more detail of procedures and observations in Methods, as suggested.  I have stated that observations of infrequent cooperative breeding in WIWAs, made mostly during the nest-building stages of some resident pairs, were part of a broader study of breeding ecology.

 Most observations of nest building yielded no evidence of helper males, and this is the case, also, for reports of infrequent cooperative breeding in other species where it has been found. 

Line 150 (182) - Yes, I would think that telemetry would be a productive addition to future studies of infrequent cooperative breeding, and I am mentioning this in suggestions for future research.

Line 157 (189) – Use of “many.”  I have reworded in text.

Line 157 (189) – Is major data based on a single nest sufficient?  I believe so.  This was a study extending over 10 years, and had even more encounters with helper males occurred, I would have noted them.  Some papers referred to are based on observation of just single events, so such few observations is not unusual.  In this study, the observations from other territories in which helping occurred (disjunct and adjacent satellite territories) in no ways were contradictory to behaviors observed in the principal breeding territory of RM and RF.  For example, in all territories observed, helpers were not chased away by the resident males, helpera did not interact sexually with the resident females, they guarded the host territories, they solicited to gain territorial acceptance, etc., etc.  I had no reason to believe relevant helper behaviors varied among host territories.  The one exception was a helper that apparently sang in a far corner of its host territory, and may have been expelled for that  transgression.  This exception seems to prove the rule, discovered in this study, that helpers do not, or should not, sing in host territories when resident males are present.  

177-180 – “METHODS” confused with “RESULTS.” – The question of what material in a paper constitutes METHODS vs RESULTS is not always as clear-cut as might be assumed, in my experience.  Some statements have elements of both.  Some statements that can be considered to be RESULTS are needed to clarify later statements that are more relevant as RESULTS.  Thus, in METHODS I frequently detected another male (9830) which turned out to be the helper.  Is this detection a RESULT, or necessary METHODS information to subsequently describe unique RESULTS attributable to 9830.  If information had to be placed in RESULTS, it would be lost as a set-up in METHODS.  I tend to err that some preliminary information needs to be placed in METHODS to better explain more important RESULTS, but I do make an effort to keep the two sections as dedicated as possible.  

220-222 -Not certain what information is thought to be amenable to statistical analysis, but I see none.  The paper is mainly descriptive of behaviors.  However, I greatly appreciate the suggestion for a table (following 3.1 – 3.9) and I do see a need for that numerical clarification.  I thus have created Table 1. 

220-222 – Use of statistics. – Not certain what specific information was thought to be amenable to statistical analysis. In terms of possibly comparing infrequent cooperative breeding of WIWAs with that reported for other warbler species, studies for those other species were done during brood care analyses, while observations with WIWAs were during nest building.  Thus, no cross-species comparisons possible.  Within WIWA observations, I could have done a stat analyses comparing the frequency of attacks on intruding males by resident male (RM) vs. attacks by helper male (HM).  However, I did not, and I question that such a comparison now would add significantly to the paper.  I have introduced Table 1, as suggested, and this shows that RM was seen to attack intruders 44 times, while HM attacked intruders 7 times.  This indicates that RM attacked more than HM, which might be expected.  Importantly, HM did defend the territory some, and to show that it did so statistically less often than did RM would not seem relevant.   

Reviewer 2 Report

Comments and Suggestions for Authors

This paper reports the suspected cooperative breeding behavior observed in the Wilson's warbler. Such low-frequency cooperative breeding behavior may exist in more species, but not all of them have been timely reported. Therefore, the results of this study hold certain significance. I have a only few points for the author to consider revising.

L21-25: “An ignored dichotomy, however, separates helping found in many individuals of some long-lived, sedentary species, from helping occasionally found in isolated breeding pairs of some short-lived, long-distance migrant species. Both types of helping are called “cooperative breeding” in the literature.” Here it emphasized that occasional helping is found in isolated breeding pairs of some short-lived, long-distance migrant species, but in fact occasional helping also occurs in long-lived species or sedentary species, and regular helping also happens in migrant species.

L44-45: Alexander Skutch provided the first detailed descriptions of cooperative breeding in birds, but the history of cooperative breeding or helping behavior in birds was not started from his publication.

L49-50: “cooperative breeding increasingly has been shown to be based on behavioral drivers, in addition to genetics”. This sentence is also not a proper statement. Behavior is the surface-level manifestation of selection pressures (it is a consequence), while the underlying drivers refer to internal mechanisms. So “behavioral driver” is not a proper phrase.

L57-58 and L 66-68: please see my comments on lines 21-25.

L115-116: For most of the reasons that the authors listed for occasional helping species (L109-115), they also apply to long-lived sedentary, regularly cooperative breeding species. So the statement that “helping in short-lived, migratory species happens for reasons that are different from reasons that it happens in long-lived sedentary species” is again not proper.

L408: “ccrtain” should be “certain”?

Author Response

1. L 21-25 – (Where helping is found) – I would have welcomed specific examples of species in which infrequent helping has been found to occur in long-lived, sedentary species. Since, prior to this manuscript, infrequent helping has not been described in the literature as behavior separate from what historically has been considered to be cooperative breeding, I am at a loss to know how infrequent cooperative breeding previously could have been described as occurring in any bird species, much less a long-lived sedentary species. 
2. Also, I am not aware of species in which kinship-related (regular) helping occurs in short-lived migratory species.  The fact that migrant species typically lack natal philopatry, it would seem rare for a first-breeding-season migrant to retrn to the territory from which it had fledged to assist its father with a brood (mothers typically change territories year-to-year).   I thought I might have found an example of a relatively short-lived migrant species that had kinship-related cooperative breeding in the Bobolink, but close exam of Beason and Trout’s paper showed that, although Bobolinks annually returned to the same general breeding area, their subsequent nests were at a distance from prior year’s nests, and thus no philopatry, and no helping based on kinship (aka, “regular” cooperative breeding).  Still, there can be exceptions to  generalizations that I do not know about.  So I will reword my paper to say “Cooperative breeding based on kinship “tends to be found” in longer-lived and sedentary avian species. whereas cooperative breeding found occasionally among species, and described in this study,” to date only has been found” in short-lived, migratory species.  These are very conservative statements. 
3. L 44-45. – I have reworded to say that Scutch provided the first detailed studies of cooperative breeding (but not necessarily that he discovered it).
4. L49-50 – OK, I am rewording the text to clarify that the more immediate reasons that cooperative breeding exists in some species is because of direct behavioral benefits (such as territory acquisition), whereas it exists in other species because of indirect benefits of kinship. Both have genetic bases, so if genetics is considered to be the ultimate drivers, then my original statement needs amending.  
5. L57-58, and 66-68 – My response to reviewer comments for lies 21 – 25 apply here also. I found a summary of the general situation that applies to tropical, sedentary, non-migratory, and long lived species versus the opposites. 
6. “Cooperative breeding in birds is more common in the tropics, particularly among altricial species. This behavior is more prevalent in species that are sedentary and maintain year-round territories, which reduces the availability of uncontested nesting territory. Cooperative breeding is also more common in species that have low mortality, small clutch sizes, high survivability of offspring, and longevity of adults, contributing to a stable population with low turnover of territories or mates. These factors, along with the long period of parental care needed by the young in the nest, make cooperative breeding advantageous for the dominant pair.” 
7. L115-116 – “Reasons for differences in why helping occurs in short-lived migratory species vs long-lived sedentary species are not proper.” I cannot disagree more.  Cooperative breeding in the two behavior groups, frequent vs. infrequent helping, is similar only to the extent that, in both groups, certain individuals help central pairs (parents or relatives in “frequent” helping groups, and unrelated territorial pairs in “infrequent” groups). And do not directly sire young. But then similarities end. The reason that “frequent” or “regular” cooperative breeding exists in a species or population is that helping is an inherent behavior of a group.  Thus, for example, in a colony of Acorn Woodpeckers, all members of the largely extended family group participate in cooperative breeding, as part of their evolved behavior.  By way of contrast, “infrequent” cooperative breeding occurs sporadically, if at all, in isolated individuals among scattered avian species or populations.  It is not inherent behavior, characteristic of entire species or populations.  The reason helping happens in certain individuals in these isolated groups is uncertain.  However, I here hypothesize that it is associated with variation in ecological conditions, rather than resulting from inherent behavior.  For example, infrequent cooperative breeding may be the consequence of a paucity of suitable breeding territories.  This is a huge basic difference in the underlying causation of the two superficially similar behaviors.  The possible causation of helping in species such as warblers opens up a whole new area of potential research, not available to studies of regular cooperative breeding.  There are other differences, too, such as regular helping tending to occur in sedentary, long-lived species, and infrequent helping tending to occur in migratory, short-lived species.  But the difference between genesis of the two types of behavior, behavioral vs. (likely) ecological, is the principal difference potentially open to future research. 
8. L408- thanks, I have corrected it.