5 March 2015 Last updated at 12:42
By Mark KinverEnvironment reporter, BBC News
A "dramatic" shift in behaviour and appearance obscured the identity of two birds on remote Indonesian islands.
The forest-dwelling birds are members of the pipit and wagtail families, but were not recognised as such, partly because they live in very different habitats to their relatives.
The madanga was considered to be a white-eye species, while the Sao Tome shorttail's affinities were uncertain.
The findings appear in the Royal Society journal Open Science.
DNA samples confirmed the their true identities, and it suggests that birds can change appearance in short periods of time.
"This is surprising because these birds do not look anything like a pipit or wagtail," explained co-author Per Alstrom from the Swedish Species Information Centre, based at the Swedish University of Agricultural Sciences.
He told BBC News that the birds also occurred in "completely different habitats".