Data from: 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.