The long-tailed finch (Poephila acuticauda) is a common species of estrildid finch found in northern Australia, from the Kimberley region to the Gulf of Carpentaria. It is a predominantly fawn-coloured bird with a pale grey head and prominent black bib and eyes. It inhabits dry savannah habitats in Australia and adapts readily to aviculture.
The adult long-tailed finch is around 16 cm in length, the weight range of males is 13.5–16.2 g and females 11.4–17.6 g. It has a prominent roundish black bib on its throat and upper chest and a long pointed black tail. It has pinkish brown upperparts with paler plumage below its bib over the lower breast and abdomen. It has a grey head, a white ear-patch, and black lores. It has black patches on its upper flanks and its rump and undertail coverts are white. The beak colour of the adult long-tailed finch varies from red through orange to yellow. Males and females are similar, except the females may be slightly duller and may have a slightly smaller bib. Females have shorter wings and tails than males on average, but their measurements, as well as throat bib size, generally lie within the range of male measurements. Furthermore, male and female plumage is indistinguishable in ultraviolet and visible light. A study published in 1999 showed that male long-tailed finches were unable to determine the sex of unfamiliar members of their species unless the latter bird declared its sex by song. Juveniles have black beaks and shorter tail feathers.
The subspecies are distinguished by the bill coloration, the nominate western group presenting a yellow colour and the eastern P. acuticauda hecki is red.