Learn more about how evolutionary biologists are revising their understanding of how evolution works. Biologists have described a form of phenotypic plasticity in fairy-wrens. The Red-backed fairy wren displays a different feather colour (red and black vs brown) depending on the nature of their social interactions. The type of plumage colour is determined by how much testosterone the male birds have prior to the breeding season. Testosterone production is regulated by social interactions between the male Red-backed fairy-wrens. If the male fairy-wren is higher ranked (more successful in attracting female attention) the feather colour becomes brighter. The colour change is not permanent. Lower ranked male fairy-wrens can change to the bright plumage colour in subsequent years.
