This is an interesting study on the relationship between key environmental variables and chick growth in seabirds, and how climate change has and will affect these relationships. The manuscript reads well throughout and is clearly focused on a cohesive story that the authors want the reader to get from their investigation. The authors clearly set out the context of their study and have four explicit and relevant objectives which they address by means of well-conducted analyses of an appropriate large multi-specific pluri-annual dataset. Their study is providing results and conclusions which should be of general interest to the readership of Journal of Avian Biology and beyond.

I just have a few general comments/questions, which might help the authors improve their message if they are addressed, in one way or another, in a revised version of the manuscript:

There is no quantification of the explanatory and/or predictive power of the selected time windows (and non-selected ones, vs. the mean throughout the full relevant set of time periods considered). I think that such information would be very helpful if you can provide it. That would be useful to know how much environmental cues over the time windows are effectively predictive of growth. Also, in the end the authors are not predicting anything for the first hatched kittiwakes because no time window was retained, although they represent the largest proportion of the population. Does it mean that their growth is not impacted by variation in the environmental variables considered at all, or rather that these variables matter throughout the full set of periods considered?

Apparently, the relevant time windows can change drastically across years. The authors provide interesting possible interpretations for this in discussion, but the exact mechanisms are unclear. I get from this that there might be major qualitative shifts in the relative importance of different periods of reproductive investment, possibly associated with rather complex biological mechanisms of compensation. Maybe I am exaggerating this? But is this issue impairing their projection analysis? In the end the authors make predictions for the future based on average relationships across the study period. Can we trust such predictions if the underlying mechanisms are in fact not so linear? If my comment make sense, I think that the authors should discuss this point in their manuscript.

The Introduction mentions the potential importance of selection and evolution, and interaction with plasticity. However, the proposed analyses and conclusions on biological implications for predicting consequences of scenarios for future climate change make little case of these issues. I appreciate that this is not the present objective to quantify and disentangle these three components, but in the end their relative importance and direction will determine the population response to climate change, and how it is shaped on the short- and longer-term. I think it would be a good thing if the Discussion somehow ties everything back to these important points in final forward-looking section. The limits and prospects of the study, and hence its contribution to ongoing research in evolutionary ecology of wild populations facing climate change, would hence appear much clearer to the reader.

Overall, I think that my three general comments above call for the authors to better delineate their attempt at predicting the future. I do see it as a useful illustration within the limits of the present models. But it is important that the readers keep in mind that there is still more complex biology and eco-evolutionary dynamics underpinning the surface patterns that are nicely highlighted in this manuscript. The present predictions might possibly be challenged by detailed knowledge of the underlying mechanisms (and there is no problem with this if properly acknowledged).

I also have a series of minor comments:

l.36: "will be adaptive..." and could thus consequently result in micro-evolutionary changes providing underlying additive genetic variation, right? This is missing a bit - sounds like you try to avoid it, or put it in the bag of things being "adaptive", but it's not enough.

l. 38-39: OK, but it is not only about stressors and constraints. There is also beneficial energetic intake that will allow the individual to grow (to stick to your context). I think you can mention this, otherwise it sounds as if life histories are only about incurring detrimental effects.

l. 45: Perhaps the transition could be made a bit smoother, by having a link with the previous paragraphs a bit more explicit?

l. 48: Specify "early life" before environmental conditions. Also specify if this is immediate and/or future survival (I guess you have both in mind)? Just to be explicit on the framework of fitness costs and benefits (necessarily implying trade-offs) which is underpinning your rationale.

l. 52-54: This is valid only if parents face a limitation in the energetic budget, right? I think this should be stated explicitly, because it sets the limits of validity of your hypothesis.

l. 52-54: OK, but here it is not clear what else it could impact ("[…] impact growth of chicks" vs. what?). Are you thinking of growth of chicks vs. energy intake of the parents, then? Or growth of chicks vs. growth later from fledgling to adulthood? Perhaps, the reader will need a clearer definition of "growth" in the context of your study system. Is it getting to adult size (in which case the parents are not supposed to "grow" anymore, right?), or do you include self-maintenance of adult mass?

l. 63: You say "each year" but you are not specifying the years during which the study took place. Same thing for the gulls.

l. 68-69: So, the only two things that alter the distribution of age-dependent (age<15 days) mass within a given cohort of chicks are: the environmental effects (on growth) and survival selection (correct?). Would it be worth specifying this to prepare the reader for correct interpretation?

l. 101-105: Do you have references or other justifications for choosing these spatial scales? This would certainly deserve a bit more explanation.

l. 122: Not clear if the random effects are on the intercept and/or slope of the growth function. And l. 131-132: are the random effects applied to all parameters of the growth curve? You say it on l. 133-135, but it should come earlier for murres. And you could be more straightforward: you have included random individual and year effects on all parameters of the growth curve for each species.

l. 123: Is this population-mean centred or individual-mean centred?

l. 146: Some justification for these lengths of time windows would be appreciated.

Finally, I have a small additional bunch of trivial editing comments:

l. 7: I tend to think that it would be helpful to specify that the period considered is something occurring within-year.

l. 11-13: I think perhaps this can be reworded to clarify the link between the general points (1 and 2) and the specific finding in the study species.

l. 91: I am not sure the grammar is OK (e.g. shouldn’t there be “that” between "temperature" and "reflects"?). Anyway, this is a very long sentence, I think you can divide into several ones.

l. 95: This is sea-ice cover in Hudson Bay, right? Perhaps use the term "sea ice cover" instead of just “ice cover” (at least in the first occurrence). Just to help the reader see what you are talking about.

l. 118-119: Worth specifying that is based on the Stan software?

l. 125-126: Either cut "a" before "non-linear mixed models" or cut the "s" of "models".

l. 128-130: Something is not correct here: you have twice the same letter ("A") for naming two different parameters. But do you need these letters? You do not use them anywhere else in the text.

l. 178-180: I think you should already give the timespan of this projection scenario here (the year in which the new environmental values are reached, 2080 as specified on l. 183).

l. 344: Add "by" after "predicted"

I thank the authors for their response to my previous comments. I think the authors did a good job at addressing the comments they received. Overall, I really enjoyed reading this revised version of the manuscript, and I think it will be of great interest to the readership of Journal of Avian Biology and beyond. I have no further comment.