Female ornamentation is frequently observed in animal species and is sometimes found as more evolutionarily labile than male ornamentation. A complex array of factors may explain its presence and variation. Here we assessed the role of female cost of reproduction and paternal care. Both factors have been pinpointed as important by theoretical studies but have not been investigated yet in detail at the interspecific level. We worked on 133 species of North temperate Passeriformes bird species for which both the clutch volume – here taken as the proxy of female cost of reproduction – and the amount of paternal care are relatively well known. Using spectrometry, we measured the whole-body colored plumage patches and quantified three metrics corresponding to brightness (i.e. achromatic component), color chromaticity (i.e. intensity), and color volume (i.e. diversity). We found a strong association between male and female color metrics. Controlling for this association, we found additional small but detectable effects of both cost of reproduction and paternal care. First, females of species with more paternal care were slightly brighter. Second, the interaction between the level of paternal care and egg volume was correlated with female color intensity: females with more paternal care tended to be more chromatic, only when their investment in reproduction was low. Together these results suggest that female cost of reproduction and paternal care are part of the multiple factors explaining variation of female coloration, besides the strong covariation between male and female coloration.

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For phylogenetic trees (phylogenies.tre): function read.nexus from package ape in R

For CSV data file: read.csv (basic package, sep = ";") in R