Size and Sex Effects on Storm-Petrels’ Maximum Load-Lift at Takeoff

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript explores the load-lifting capacity during takeoff of the Least Storm-Petrel (LSP) and the Black Storm-Petrel (BSP), on Isla Partida Norte in the Gulf of California. The authors highlight the importance of lifting capacity for effective foraging, survival, and reproductive success in seabirds. This timely research could be vital for understanding and addressing the forthcoming challenges that seabird populations face.

In this study, sex was determined using DNA analysis. The researchers assessed the maximum carrying capacity by attaching weights to the birds to measure their lifting abilities during takeoff (48 LSP and 23 BSP). The average LSP body mass was 18.93 grams, while BSP averaged 54.80 grams. LSP managed to lift loads equal to 37.25% of its body mass, whereas BSP lifted 30.62%. While females generally showed a higher body mass and lifting capacity, these differences were not statistically significant.

Despite being smaller, the results indicate that LSPs have a higher load-lifting capability than BSPs. The study also suggests environmental factors, such as El Niño events, that can influence the seabirds.

Interestingly, both LSP and BSP exhibit smaller body sizes compared to historical data, with LSPs showing a greater relative lifting capacity. The authors should consider discussing this very interesting point of historical downsizing, which has wide-ranging ecological implications.

Overall, the writing is coherent and well-organized, and the flow of the story is good.

However, I have a few suggestions for improving the manuscript further:

Abstract - focus on the key findings and their broader implications.

As someone not deeply rooted in seabird research, I believe the authors should justify their chosen methods and statistical analyses more clearly. A rationale for the experimental design will help readers understand your approach better. Additionally, a discussion on sample size and its implications for statistical power and the generalization of the results would strengthen the readers' understanding of your thought process.

Finally, the authors might consider outlining recommendations for future research directions. These can either be more general or site specific as per their personal experiences.

Author Response

RESPONSE TO REVIEWER 1 (below each comment where corresponds)

 

Comments and Suggestions for Authors

The manuscript explores the load-lifting capacity during takeoff of the Least Storm-Petrel (LSP) and the Black Storm-Petrel (BSP), on Isla Partida Norte in the Gulf of California. The authors highlight the importance of lifting capacity for effective foraging, survival, and reproductive success in seabirds. This timely research could be vital for understanding and addressing the forthcoming challenges that seabird populations face.

In this study, sex was determined using DNA analysis. The researchers assessed the maximum carrying capacity by attaching weights to the birds to measure their lifting abilities during takeoff (48 LSP and 23 BSP). The average LSP body mass was 18.93 grams, while BSP averaged 54.80 grams. LSP managed to lift loads equal to 37.25% of its body mass, whereas BSP lifted 30.62%. While females generally showed a higher body mass and lifting capacity, these differences were not statistically significant.

Despite being smaller, the results indicate that LSPs have a higher load-lifting capability than BSPs. The study also suggests environmental factors, such as El Niño events, that can influence the seabirds.

Interestingly, both LSP and BSP exhibit smaller body sizes compared to historical data, with LSPs showing a greater relative lifting capacity. The authors should consider discussing this very interesting point of historical downsizing, which has wide-ranging ecological implications.

Overall, the writing is coherent and well-organized, and the flow of the story is good.

However, I have a few suggestions for improving the manuscript further:

Abstract - focus on the key findings and their broader implications.

1. We have focused on the key findings and broader implications, as can be seen in lines 26-28 (Abstract section). Now, we acknowledge that “Although smaller, LSP lift more than BSP, and environmental factors like El Niño also influence seabird performance”.

As someone not deeply rooted in seabird research, I believe the authors should justify their chosen methods and statistical analyses more clearly. A rationale for the experimental design will help readers understand your approach better. Additionally, a discussion on sample size and its implications for statistical power and the generalization of the results would strengthen the readers' understanding of your thought process.

1. We followed this recommendation by the reviewer. Now, we include the following ideas: 1) Justification of chosen methods. The methodology established by Marden [6] was selected due to its widespread use and validation in avian flight performance studies, ensuring comparability and scientific rigor. The incremental loading technique, using a known weight attached to the legs, allows for a precise and repeatable assessment of maximum carrying capacity while mimicking natural load-bearing scenarios like prey transport. To minimize stress and ensure ethical treatment, the protocol was adapted to include nighttime handling, red-light conditions, and sufficient rest between trials—measures supported by best practices in avian field research. The absence of observable exhaustion further supports the appropriateness of this approach. Conducting the trials in a wind-sheltered tent ensured standardized environmental conditions, reducing confounding variables such as gusts and thermal drift. Additionally, the calculation of maximal lift force using the method of Ortega–Jiménez et al. provided a robust and physiologically grounded measure of performance. Together, these elements offer a reliable, ethical, and scientifically defensible method for evaluating load-lifting capacity in storm-petrel species. 2) Statistical analyses. Student’s t-test was employed to assess whether statistically significant differences exist between groups—specifically, between sexes or species of storm-petrels. This test is appropriate for comparing the means of two independent groups when the dependent variable (e.g., lift force or carrying capacity) is continuous and approximately normally distributed. Prior to analysis, data were checked for normality and homogeneity of variances, ensuring the assumptions of the t-test were met. Given the two-group comparison and the scale of measurement, the t-test provides a straightforward and powerful method to detect group differences.

Finally, the authors might consider outlining recommendations for future research directions. These can either be more general or site specific as per their personal experiences.

1. We included the following paragraph: Future research should investigate the physiological and biomechanical mechanisms behind the LSP’s greater relative load-carrying capacity and energy efficiency, including muscle composition and wing dynamics. Comparative studies across different populations may clarify whether the observed reductions in body mass and wingspan reflect geographic, ecological, or climatic influences. Given the potential impact of environmental stressors like El Niño, longitudinal studies ex-amining how such factors affect flight performance and body condition are recom-mended. Additionally, tracking individuals across life stages and seasons could re-veal ontogenetic or temporal changes in carrying capacity. While no significant sex-based differences were found, further research with larger sample sizes may uncover subtle variations. Finally, integrating aerodynamic modeling with field tracking would also enhance understanding of flight performance under natural conditions, and examining the long-term fitness consequences of lift efficiency may provide insight into the ecological significance of these traits.

 

Reviewer 2 Report

Comments and Suggestions for Authors

Title: explain the novelty of your study compared to

Maximum load-carrying during takeoff of Leach's Storm-Petrel Oceanodroma leucorhoa and Cassin's Auklet Ptychoramphus aleuticus

Abstract

Comment: As it occurs in many other places worldwide, seabirds within the Gulf of California for- 16 age for themselves and their chicks by carrying heavy loads over long distances to the nest. The 17 extra weight the bird can lift during takeoff thus becomes an important factor for efficient 18 foraging. Although some studies have addressed this, most did not consider fac- 19 tors such as lifting force, maximum induced power, or aerobic and anaerobic performance. How- 20 ever, no important differences among individuals (i.e., size between individuals or sex) have been addressed. Too long. Reduce this section with short and direct ideas.

Comment: In both species, carrying ca- 24 pacity was found to be independent of individual size, but the Least Storm-Petrel managed to 25 takeoff with a higher proportion of its total mass than the Black Storm-Petrel. No differences were 26 found in carrying capacity associated with sex. Possible implications of these results for each of 27 the species are discussed. Please develop this part. Since this presents the results, which are the most important goals of the study.

Comment: Mention the limits of your approach and suggest new guidelines.

Introduction

Comment: The Gulf of California (hereafter, GoC) is recognized as a region of high species rich- 31 ness, many of which are endemic. References.

Comment: lines 31-65: loo long. Please divid it into clear and one-idea paragraphs. You can start by the the idersity in the Gulf and the activities of birds, you can cite examples for species (i.e. the study species).

Comment: In the second paragraph, we suggest to discuss the studied parameters (weight of takeoff, etc).

Comment: we found im- 70 portant differences between the size and weight of both species currently recognized and 71 those found in our study. Also, we observed differences in the maximum extra load sup- 72 ported at takeoff between species, but not in terms of sex; however, although it was found 73 that in all cases the females and males of each species achieved an efficient anaerobic take- 74 off, not all individuals achieved an aerobic takeoff. These are results. Please mention the novelty of your study. The specificity of the studied parameters and their utility.

Materials and methods

Study zone

Comment: add a map to clarify the sampling sites.

Comment: The study area was fused with data collection.

Comment: please separate them.

 Statistical analysis

Comment: did you tested the normality of data.

Comment: mention the software used and replications.

Results

Sex determination of BSP and LSP individuals

Comment: Present results in a figure :

Discussion

Comment: Table 6. P: displace it to results.

Conclusions

Comment: please start by the objective, mentions the most important conclusions supported by results.

Comment: mention the implications of your results, limits of the approach, and the avenues for future studies.

 

 

 

 

 

 

 

Author Response

RESPONSE TO REVIEWER 2 (below each comment where corresponds)

Comments and Suggestions for Authors

Title: explain the novelty of your study compared to

Maximum load-carrying during takeoff of Leach's Storm-Petrel Oceanodroma leucorhoa and Cassin's Auklet Ptychoramphus aleuticus

1. While previous work, such as the study on Leach's Storm-Petrel and Cassin's Auklet, focused on interspecific differences in maximum load-carrying capacity and takeoff dynamics, the present study offers several novel contributions. First, it examines two closely related storm-petrel species (LSP and BSP) within the same ecological guild, allowing for finer-scale comparisons of morphology, muscle mass proportion, and lift-to-power ratios under controlled conditions. Second, it uniquely highlights that despite being smaller, LSPs exhibit greater relative load-carrying efficiency and a higher lift-to-power ratio, suggesting a functional advantage in energy expenditure not previously reported. Third, this study incorporates sex-based comparisons and finds that, although females tend to have higher absolute performance metrics, sex has no significant effect on relative carrying capacity—a dimension largely unaddressed in the earlier literature. Lastly, by comparing current morphometric data with historical records, this work identifies potential temporal or environmental shifts in body size, prompting ecological questions about climate or habitat-driven adaptation. Together, these elements contribute novel insights into the biomechanics, energetics, and ecological implications of flight performance in small seabirds.

Abstract

Comment: As it occurs in many other places worldwide, seabirds within the Gulf of California for- 16 age for themselves and their chicks by carrying heavy loads over long distances to the nest. The 17 extra weight the bird can lift during takeoff thus becomes an important factor for efficient 18 foraging. Although some studies have addressed this, most did not consider fac- 19 tors such as lifting force, maximum induced power, or aerobic and anaerobic performance. How- 20 ever, no important differences among individuals (i.e., size between individuals or sex) have been addressed. Too long. Reduce this section with short and direct ideas.

1. We have reduced that section of the paragraph. Now, this section is shorter, with direct ideas: In the Gulf of California, seabirds carry heavy loads to feed their chicks, making takeoff capacity crucial for foraging. While some studies explore this, few consider lift force, induced power, or aerobic vs. anaerobic performance. Moreover, differences between individuals—such as size or sex—remain largely unexamined, leaving gaps in understanding seabird flight efficiency.

Comment: In both species, carrying ca- 24 pacity was found to be independent of individual size, but the Least Storm-Petrel managed to 25 takeoff with a higher proportion of its total mass than the Black Storm-Petrel. No differences were 26 found in carrying capacity associated with sex. Possible implications of these results for each of 27 the species are discussed. Please develop this part. Since this presents the results, which are the most important goals of the study.

1. We elaborate on this, as suggested by the reviewer. Now, it includes the following sentences: This study found that both storm-petrel species were smaller and lighter than previously reported, yet LSPs carried relatively heavier loads than BSPs. Although BSPs had higher absolute values for mass and lift, LSPs were more energy efficient. Muscle mass proportions were similar and typical for takeoff. No significant sex-based differences were found. Both species used aerobic and anaerobic takeoff, with anaerobic flight likely being more efficient

Comment: Mention the limits of your approach and suggest new guidelines.

Introduction

Comment: The Gulf of California (hereafter, GoC) is recognized as a region of high species rich- 31 ness, many of which are endemic. References.

1. We have included three references. These sources collectively affirm the Gulf of California's exceptional biodiversity and high levels of endemism, reinforcing its importance as a region of significant ecological value.

Comment: lines 31-65: loo long. Please divid it into clear and one-idea paragraphs. You can start by the the idersity in the Gulf and the activities of birds, you can cite examples for species (i.e. the study species).

1. We have followed this recommendation. Now, that paragraph was divided into three paragraphs, each containing separate ideas.

Comment: In the second paragraph, we suggest to discuss the studied parameters (weight of takeoff, etc).

1. We followed this recommendation. Now, we added the following sentences in that paragraph: “Maximum Load-Lift at Takeoff refers to the greatest amount of extra weight a bird can carry while still being able to successfully take off from the surface. It reflects the bird’s lift-generating ability relative to its body mass and is influenced by factors such as wing size, muscle strength, and flight technique. It is a key indicator of flight performance and energy capacity. On the other hand, a takeoff model such as Marden's model, is a biomechanical framework used to estimate a bird’s maximum load-lifting capacity and related flight parameters. It typically incorporates variables like body mass, wing area, muscle mass, and induced power to predict how much weight a bird can lift during vertical or near-vertical takeoff, and to assess flight efficiency and energy use.”

Comment: we found im- 70 portant differences between the size and weight of both species currently recognized and 71 those found in our study. Also, we observed differences in the maximum extra load sup- 72 ported at takeoff between species, but not in terms of sex; however, although it was found 73 that in all cases the females and males of each species achieved an efficient anaerobic take- 74 off, not all individuals achieved an aerobic takeoff. These are results. Please mention the novelty of your study. The specificity of the studied parameters and their utility.

1. In this response-by-point (see above), we have addressed the novelty of this study. Therefore, we incorporate the following sentences: While previous work, such as the study on Leach's Storm-Petrel and Cassin's Auklet, focused on interspecific differences in maximum load-carrying capacity and takeoff dynamics, the present study offers several novel contributions. First, it examines two closely related storm-petrel species (LSP and BSP) within the same ecological guild, allowing for finer-scale comparisons of morphology, muscle mass proportion, and lift-to-power ratios under controlled conditions. Second, it uniquely highlights that despite being smaller, LSPs exhibit greater relative load-carrying efficiency and a higher lift-to-power ratio, suggesting a functional advantage in energy expenditure not previously reported. Third, this study incorporates sex-based comparisons and finds that, although females tend to have higher absolute performance metrics, sex has no significant effect on relative carrying capacity—a dimension largely unaddressed in the earlier literature. Lastly, by comparing current morphometric data with historical records, this work identifies potential temporal or environmental shifts in body size, prompting ecological questions about climate or habitat-driven adaptation. Together, these elements contribute novel insights into the biomechanics, energetics, and ecological implications of flight performance in small seabirds.

Materials and methods

Study zone

Comment: add a map to clarify the sampling sites.

10. The information on sampling sites has been published elsewhere (see https://journals.sagepub.com/doi/10.1177/1940082920949177). We consider that this information has been well described already, and the source cited properly. Therefore, we consider that redrawing the same map with exactly the same information is not strictly necessary.

Comment: The study area was fused with data collection.

Comment: please separate them.

1. We followed this recommendation and separated them.

 Statistical analysis

Comment: did you tested the normality of data.

1. Yes, both normality and homogeneity of variances were tested, ensuring the assumptions of the Student’s t-test were met. We included a sentence explaining and clarifying this.

Comment: mention the software used and replications.

1. We have added the software used and appropriate citation were corresponds.

Results

Sex determination of BSP and LSP individuals

Comment: Present results in a figure :

1. We have included the corresponding figure (Figure 1).

Discussion

Comment: Table 6. P: displace it to results.

1. We have displaced table 6 from the Discussion section to the Results section.

Conclusions

Comment: please start by the objective, mentions the most important conclusions supported by results.

1. We have completely rewritten this section, highlighting the most important conclusions supported by the results, as suggested by the reviewer.

Comment: mention the implications of your results, limits of the approach, and the avenues for future studies.

1. We have added a paragraph at the end of the previous section (Discussion), explaining the implications of your results, limits of the approach, and the avenues for future studies. as suggested by the reviewer.

 

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors improve the manuscript very well. I accept the article in  this form