DOI: 10.5061/dryad.8kprr4xmq
title: Data from: Plumage and eggshell colouration covary with the level of sex-specific parental contributions to nest building in birds

description: Interspecific variation in sex-specific contributions to prenatal parental
 care, including avian nest building, remain poorly understood. Here, we
 examined whether the colouration of the parents and of their eggs covary
 with sex-specific nest-building contributions in 521 species of Western
 Palearctic birds. Having colourful plumages and laying colourful eggs are
 both costly because of the deposition of pigments (in feathers and eggs)
 and/or forming costly nanostructural substrates (in feathers), and so it
 is expected that those costs are traded-off against the costs of nest
 building. We therefore tested two predictions of this trade-off
 hypothesis, namely that species in which females alone build nests (1)
 exhibit sexual plumage dichromatism in that females are less colourful
 than males and (2) lay less colourful eggs. Using a
 phylogenetically-informed comparative approach, we found support for the
 first prediction so that species in which females build nests alone or
 together with males are more likely to be dichromatic in plumage.
 Meanwhile, regarding the second prediction, contrary to our expectation,
 we found that species in which females build nests alone or together with
 males are more likely to lay colourfully pigmented eggs relative to
 species in which only males build nests. This suggests that sex
 differences in plumage colouration and egg colouration covary in a complex
 manner with female pre-copulatory investment in reproduction at the
 interspecific level.
description: We quantified nest-building contributions, and the colouration of
 parent birds and their eggs of 521 bird species, included in the Birds of
 the Western Palearctic book series. Nest building contributions were
 classified as being ‘male’ if males build nests alone, ‘female’ if females
 build nests alone, ‘both’ if both parents contribute to nest building, and
 ‘neither’ if none of the parents contribute to nest building (e.g.
 seabirds). Sexual plumage dimorphism was classified as being either
 present or absent. Data on clutch sizes and body mass of males and females
 were extracted from the same source and were averaged per species.
 Eggshell colour was determined by reading species descriptions and by
 inspecting colour plates and was defined as being blue, brown, or white.
 We deemed blue or brown but not white (unpigmented) as pigmented by
 predominantly biliverdin or protoporphyrin IX, respectively.
description: Variable names and descriptions Species -
 scientific name of bird species<br>Nest_builder - nest builder sex
 (both, male, female, neither)<br>Colour_dichromatism - sexual
 plumage dichromatism (yes/no)<br>Egg_colur - egg colouration (blue,
 brown, white)<br>Mean_BM - average adult body mass in
 grams<br>Clutch_size_mean - average clutch size
description: # Data from: Plumage and eggshell colouration covary with the level of
 sex-specific parental contributions to nest building in birds
 ### Methods We quantified
 nest-building contributions, and the colouration of parent birds and their
 eggs of 521 bird species, included in the Birds of the Western Palearctic
 book series. Nest building contributions were classified as being ‘male’
 if males build nests alone, ‘female’ if females build nests alone, ‘both’
 if both parents contribute to nest building, and ‘neither’ if none of the
 parents contribute to nest building (e.g. seabirds). Sexual plumage
 dimorphism was classified as being either present or absent. Data on
 clutch sizes and body mass of males and females were extracted from the
 same source and were averaged per species. Eggshell colour was determined
 by reading species descriptions and by inspecting colour plates and was
 defined as being blue, brown, or white. We deemed blue or brown but not
 white (unpigmented) as pigmented by predominantly biliverdin or
 protoporphyrin IX, respectively. ### Usage notes Variable names and
 descriptions Species - scientific name of bird species Nest_builder - nest
 builder sex (both, male, female, neither) Colour_dichromatism - sexual
 plumage dichromatism (yes/no) Egg_colur - egg colouration (blue, brown,
 white) Mean_BM - average adult body mass in grams Clutch_size_mean -
 average clutch size