Nanoscale millefeuilles produce iridescent bill ornaments in birds

Colours are well studied in bird plumage, however studies on colours in other integumentary structures remain scarce. In particular, iridescent colours from non-plumage structures are undescribed in birds. Here, we show that a multilayer of keratin and lipids are sufficient to produce the iridescent bill of Spermophaga haematina. Furthermore, the observation that the male bill is presented to the female under differengt angles during display, provides support for the hypothesis that iridescence evolved in response to sexual selection. Not only is this the first report on an iridescent bill, it is only the second instance of iridescence in birds in which melanosomes are not involved. These results are thus exciting, as they suggest that birds utilize an even wider array of physical phenomena to produce colouration, and should further stimulate research on non-plumage integumentary colours., , , This datasets conatains 2 R scripts.

R_Script_plotting_graphs.RMD is used to plot the simulated and measured reflectance spectra. It depends on bluebillref.csv as an input file.
evo_history.R is used to estimate the ancestral state of colour mechanisms. It depends on state data (bill_final2.csv) and a phylogenetic tree (birdtree.tre)

bill_final2.csv has tree columns: column 1 contains the species name, column 2 (final) contains the colour mechanism based on museum specimens, column 3 (final2) contains the mechanism based on photos and descriptions.

Other files include:

-Supplementary data 1 - Reflectance data which contains reflectance data across different angles (55/60/65/70/75/80/85/90, for multiple patches (_1/2).

-Supplementary data 2 - specimens checked. This file has 6 columns: \"Species\" describes the species name, \"sex\" describes the sex, \"year collection\" describes the year the specimen was collected, \"Locality\" where it was collected, \"Voucher number\" corresponds to the u...