Pteropus dasymallus is widely distributed on islands throughout the western edge of the Pacific Ocean. The Formosan flying fox, P. d. formosus, is an endemic subspecies in Taiwan found mainly on Lyudao; it was previously thought to have been extirpated. Since 2005, intensive surveys have been conducted to investigate the residency, population size and plant resource utilization of P. dasymallus in Taiwan. Interviews were carried out to investigate its former abundance and the causes of population decline. In Taiwan, P. dasymallus is in a state of ongoing oceanic dispersal and colonization and has considerably expanded its geographic range. In addition to remaining in its historic habitat on Lyudao, P. dasymallus has also established colonies on Gueishan Island and in Hualien on Taiwan's main island in the past few decades. The total population size is estimated to be 240 individuals, and this number is on the rise. Approximately three-quarters of the entire population (73.64%) was found on Gueishan Island. The sex ratio was strongly skewed toward males. A total of 40 plant species were recorded as being used by the flying fox for food, roosts or perches. More agricultural and horticultural plant species were used by the flying fox in urban Hualien. According to the interviews, flying foxes were abundant on Lyudao, but their number dramatically declined from the 1970s to the mid-1980s, mainly due to commercial hunting. Maintaining a sufficient population size and genetic variability is fundamental to the long-term survival of the flying fox. Enforcing conservation laws, restoring habitats, controlling invasive species and improving public awareness are the main steps in the recovery and sustainability of the flying fox population.
Keywords: Insular ecosystem; Interoceanic dispersal; Local extirpation; Pteropodidae; Ryukyu flying fox.