Dyacopterus spadiceus - Dayak Fruit Bat - Peninsular Malaysia
Female, Field Cat. No. 920825.5, Kuala Lompat, Krau Game Reserve, Peninsular Malaysia, 1992. C M Francis

The Dayak fruit bat or Dyak fruit bat (Dyacopterus spadiceus) is found in Sumatra, Borneo, the Philippines, and the Malay Peninsula. Males of the species have large, swollen nipples that lactate. The Dayak fruit bat is the only known mammalian species where male lactation might be standard. Male nipples are still smaller than those of females and produce only about a tenth as much milk. The cause and purpose of this phenomenon is unknown, it may be a side effect of phytoestrogens in leaves in the bats' diet, or it may be an actual adaptation to feed their young.