The fantail species of Australasia typically build a compact cup-shaped nest of vegetable fibre bound externally with spider web, with a ‘tail’ extending from the base. The discovery of an active Dimorphic Fantail Rhipidura brachyrhyncha nest in montane Papua New Guinea revealed an atypical nest externally composed of moss, but without a ‘tail’. The coloration and size of the egg were similar to those of other Australasian fantails. A clutch-size of one in montane fantail species and usually two in lowland species contributes toward an understanding that clutch-size decreases with altitude in many open-cup-nesting New Guinean fantails, monarchs, robins, honeyeaters and birds-of-paradise but not in bowerbirds, Myzomela and Meliphaga honeyeaters, berrypeckers, jewel-babblers, woodswallows and whistlers.