Nest defence behavioural reaction norms: testing life-history and parental investment theory predictions

Predation is the primary source of reproductive failure in many avian taxa and nest defence behaviour against predators is hence an important aspect of parental investment. Nest defence is a complex trait that might consistently differ among individuals (personality), while simultaneously vary within individuals (plasticity) according to the reproductive value of the offspring. Both complementary aspects of individual variation can influence fitness, but the causality of links with reproductive success remains poorly understood. We repeatedly tested free-living female great tits (Parus major) for nest defence (hissing) behaviour across the nesting cycle, by presenting them with a model predator. Hissing behaviour was highly repeatable but, despite population-level plasticity, we found no support for individual differences in plasticity. Path analysis revealed that repeatable differences in hissing behaviour had no direct effect on nest success or fledgling number. However, our best supported path-model showed that more fiercely hissing females laid smaller clutches, with clutch size in turn positively influencing fledgling number, suggesting that females are most likely facing a trade-off between investment in nest defence and reproduction. Strong stabilizing selection for optimal plasticity, in combination with life-history trade-offs, might explain the high repeatability of nest defence and its link with reproductive success.


20-Feb-2019
Dear Mr Thys, The editors assigned to your paper ("Nest defence behavioural reaction norms: testing life history and parental investment theory predictions") have now received comments from reviewers. We would like you to revise your paper in accordance with the referee and Associate Editor suggestions which can be found below (not including confidential reports to the Editor). Please note this decision does not guarantee eventual acceptance.
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Once again, thank you for submitting your manuscript to Royal Society Open Science and I look forward to receiving your revision. If you have any questions at all, please do not hesitate to get in touch. Dear Dr. Thys, I have received the comments from two expert reviewers and as you can find they were both pleased by the degree to which you addressed issues raised int he past. However one reviewer continues to emphasize the importance of more equitably discussing the three possible models that received relatively equal support. The reviewer acknowledges that you have now mentioned this point, but they indicate that you have not done this sufficiently, such that you appear to favor one interpretation over others that statistically are equally good. I think you should more directly address this issue. There are several way sin which I think you could accomplish this, for example, you could walk back your interpretation and/or provide deeper discussion of the other ways to interpret the results based on the other models, or you can provide justification for why your preferred model deserves more prominence. Whatever you decide, I think that it is an important enough issue that it merits some more thought. This point notwithstanding, you have produced a nice study that clearly has generated some positive interest and I look forward to receiving your responses.
Editor comments: It appears that the reviewers are generally satisfied with the revisions, with one exception detailed by the AE. Please address this in your next version, and thanks for submitting.

Comments to Author:
Reviewers' Comments to Author: Reviewer: 1 Comments to the Author(s) I reviewed this manuscript previously when it was submitted to Proceedings of the Royal Society B. Generally, I think the majority of the concerns raised in the initial review were adequately addressed with the revisions, with one important exception; the interpretation of the strength of support for the alternative path analysis models. Models 1-3 are effectively all equally well supported (within 3 AIC of best model), and they each provide very different interpretations of the effect of hissing behaviour on breeding parameters and nest success. I think the only conclusion that can be drawn from this is that the role of hissing behaviour in shaping these other parameters is totally unclear. Although the authors vaguely acknowledge this in the discussion,they go on to primarily interpret the results of model 3. Further, the abstract presents the results of model 1 without clarifying that there are two alternative interpretations that are equally well supported, including no relationship between hissing and any of the other parameters.

Recommendation?
Accept as is

Comments to the Author(s)
The authors are now explicit about their criteria (delta AIC >2) for considering a significant difference between models, but clarify that two models were only marginally worse that this.  table files for each table  3) a caption file containing captions for the tables and figures 4) an editable version of the manuscript (Word or Latex preferred).
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