May 2020
Vol 6, Issue 20

About The Cover

Cover image expansion

ONLINE COVER Structural colors that arise from the branches within feathers, manifesting in a range of iridescent hues, have been observed in many modern-day birds but have never been reported in members of the palaeognath clade, which includes the cassowary. This large, flightless bird has a killer nail fitted to its second toe that often earns it the label "the world's most dangerous bird." To investigate the eye-catching feathers of this uninviting bird, Eliason and Clarke compared the reflectance ratios of 32 feathers from 17 palaeognath species. They used atomic force microscopy and transmission electron microscopy to understand the structural basis of cassowary sheen, finding that their feathers are not noticeably smoother than those of related species and that they possess no keratin film. This led the researchers to measure aspects of feather microstructure with light microscopy, noting the differences between shiny and matte species. Eliason and Clarke conclude that the cassowary achieves its luxuriously glossy plumage through modifications to feather shape, similar to the hair structure of some mammals with scale-like body covering. [CREDIT: JOEL SATORE-NATIONAL GEOGRAPHIC PHOTO ARK]