The species range of the red-backed fairy-wren. The species occurs across northern Australia, in the Cape York Peninsula, and along much of the east coast (a). The range of the crimson-backed, shorter-tailed M. m. cruentatus subspecies (b) is shaded dark grey and the range of the orange-backed, longer-tailed M. m. melanocephalus subspecies (c) is shaded light grey. Field observations have led to the subjective delineation of a morphological contact zone in the northeast. The solid line represents the Carpentarian Barrier, a biogeographic barrier across which the subspecies are genetically differentiated. The dashed line represents the eastern contact zone as we have defined it based on reflectance spectrometry of feather samples. Stars indicate sampling localities (N = 24) and white stars indicate three locations not included in the plumage color and male tail length dataset.