This bird’s occurrence in a restricted habitat of one very small island makes it extremely vulnerable to natural disasters like fires and hurricanes, or to introduced diseases, and especially to the accidental introduction of non-native predators (3). Indeed, the introduced house mouse Mus musculus poses the greatest present threat through competition and predation (2). Buntings are found at low density in lowland areas where mice are abundant (2), and experiments with ‘dummy’ eggs imply that mouse predation on their nests is very high (5). Thus, researchers think the bird may have been forced by these mice from the best nesting sites into less suitable upland regions (5). Over the last 15 years, the proportion of juveniles in the population has declined from 50% to 20%, this appears to indicate that there are now too few young surviving to reproductive age to sustain the population.
The accidental introduction of the black rat Rattus rattus from Tristan is also a huge potential threat, having caused devastation on Tristan to a number of bird species. Worryingly, a dead rat was discovered in a packing case in 1967, another was found on the Gough supply ship in 1974, and there was an unconfirmed rat sighting on the island in 1983 (2).