There are two microchiropteran bat species in New Zealand: the long-tailed bat Chalinolobus tuberculatus and the short-tailed bat Mystacina tuberculata. Both species coexist on Little Barrier Island in the Hauraki Gulf, New Zealand. In this study we examined the diet of M. tuberculata, and the activity levels of both bat species associated with Metrosideros excelsa, a native flowering plant and potential nectar source, on Little Barrier Island. Between November 1994 and February 1996, M. tuberculata were caught in mist-nets, and their faecal pellets were collected for later dietary analysis. In addition, pollen samples were collected from the fur of bats caught during December 1995 and January 1996. Faecal analysis showed that M. tuberculata on Little Barrier Island exhibits a high degree of omnivory, with its diet comprising flying and non-flying arthropods, and also pollen and other plant material. During December 1995 and January 1996, the activity levels of both bat species associated with flowering and non-flowering M. excelsa trees were investigated by recording bat echolocation calls with automatic detecting and recording units. Significantly higher numbers of M. tuberculata echolocation calls were recorded near flowering M. excelsa trees than near non-flowering ones, whereas the numbers of C. tuberculatus calls did not differ significantly between flowering and non-flowering trees. These results contribute further to the existing evidence for nectarivory in M. tuberculata.