PREreview of Carotenoid-dependent plumage coloration is associated with reduced male care in passerine birds

Overall summary:

This study uses phylogenetic comparative analyses across 350 passerine bird species to demonstrate a correlation between carotenoid-rich food consumption and carotenoid-dependent plumage coloration, linking this with an inverse correlation with male investment in offspring care. The authors use data from published sources, particularly relying on data from: a) Liker et al, 2015 on relative investment in parental care by each sex in passerine species, from which they calculated a mean relative ration male participation score; and b) Thomas et al, 2014 on species with males with carotenoid-dependent coloration, from which they scored the extent of coloration and amount of carotenoids needed.

This manuscript describes the methods and rationale for analysis in great detail, with the authors making extensive use of a range of carefully-considered variables to inform their modeling, which is used to test two questions:

1. Does the presence of carotenoid-dependent coloration indicate male tendency to invest in parental care?

2. Does the magnitude of the signal give a more reliable indication of any tendency?

The data analyses are very well explained, with thorough evaluation of the work in context provided. The authors critique the results extensively in the discussion, including discussion of limitations and potential future research questions. The work uses methodologies that are well-rationalized and systematic.

Major Comments:

I have no major comments.

Minor Comments:

In Figure 1, does the scale of parental care represent less male parental care at 0.333, and most at 3.333? What is the meaning of these numbers?

While interesting to look at, what is Figure 1 trying to convey to the reader? Are we to take from this that there is some kind of conclusion about the phylogenetic distribution of carotenoid-dependent coloration, and/or of male paternal care?

Conflicts:

I have no conflicts to report; I have not been involved with nor discussed this work with the author. I do not stand to gain or suffer financially or otherwise from this publication.

License:

This review is published under a CC-BY license.

Competing interests

The author declares that they have no competing interests.