Feeding behavior of the Orii's flying-fox, Pteropus dasymallus inopinatus, on Mucuna macrocarpa and related explosive opening of petals, on Okinawajima Island in the Ryukyu Archipelago, Japan

The role of the Orii's flying-fox, Pteropus dasymallus inopinatus, in the reproduction of Mucuna macrocarpa was investigated through captive and wild observations on Okinawajima Island in the Ryukyu Archipelago, Japan. When Orii's flying-fox fed on flowers of M macrocarpa, it pushed its nose to the basal portion of the flowers to feed on nectar. This caused the hard petals of flowers to explode and consequently opened the carina. When a flying-fox's face pointed in the same direction as a flower, there was a significantly higher explosive opening rate compared with approaches from the side or the opposite direction (chi(2) test; P < 0.001). In total, in the captive setting, 32.2% of the flowers exhibited explosive opening. During such events, stamens with pollen and pistils emerged and attached to the throat and forehead of the flying-fox. Other main flower visitors were the brown-eared bulbul, the Japanese white-eye, the Japanese bush warbler, and the honeybee, but they did not stimulate explosive opening. These observations demonstrate that the Orii's flying-fox is the only explosive opener and the primary pollinator of this flower. On the other hand, flying-foxes sometimes damaged flowers. However, this does not appear to be a serious problem for M macrocarpa, which has a large number of flowers.