sentences:  Almost a quarter of all rail species have conservation concerns, and flightless island species are particularly at risk, at least 15 species having become extinct since 1600.The estimated population of the invisible rail is 3,500–15,000 birds, and its restricted range and small population mean that the species is classified as vulnerable by the International Union for Conservation of Nature (IUCN), although this rail is so poorly known that it may be more common than the estimates suggest.Habitat loss has occurred through commercial harvesting of the sago, or conversion to rice cultivation and fishponds.