Detecting animals by identifying their DNA in water is a valuable tool for locating and monitoring species that are difficult to detect through other survey techniques. We developed a test for detecting the endangered Gouldian finch Erythrura gouldiae, a small bird endemic to northern Australia. Only 1 previous study has reported an environmental DNA (eDNA) test that unequivocally identifies a bird species using the water bodies from which they drink. In controlled aviary trials with a pair of Gouldian finches, first detection in 200 ml of water occurred after as little as 6 h, but the detection rate was higher at 30 h. DNA persisted in water exposed to the sun for <12 h and in the shade for 12 h. In trials with 55 finches, persistence was up to 144 h. The eDNA test for finches and the Gouldian finch-specific test were positive for waterholes where Gouldian and other finch species were observed each morning over 3 d. Importantly, where no Gouldian finches were observed for up to 72 h prior to water sampling, the Gouldian test was negative. Where other species of finch but no Gouldian finch were observed and counted, the finch test was positive, but the Gouldian finch test was negative. This approach could be developed for broadscale monitoring of this endangered species, and potentially applied to a much broader range of terrestrial species that shed DNA into water bodies.