Flashy and Functional: Interplay of Iridescence and Hydrophobicity in Hummingbird Feathers

In birds, iridescent feathers feature flat subcomponent barbules to maximally reflect light, contributing to vivid coloration. Such structure is distinct from non-iridescent feathers, where barbules are spaced and angled to create an arrangement of keratin and air. The differences in topology between iridescent and non-iridescent feathers lead to differences in wettability, where iridescence comes with the trade-off of decreased hydrophobicity. As a result, the coverage of iridescent vs. non-iridescent feathers on birds reflect necessities for either colorful appeal or functional hydrophobicity. In this investigation, we study the peculiar exception to this relationship, found in the hierarchal structure of hummingbird feathers that are both iridescent and super-hydrophobic. We perform optical and wettability measurements for different feathers found on the ruby-throated hummingbird and discuss the optimization of geometry that allows for super-hydrophobicity to coexist with iridescence.