Bats are a diverse group of native mammals, the most conspicuous of which are the Grey-headed Flying-fox (Pteropus poliocephalus), or fruit bats. In 1981 a camp established in the Royal Botanic Gardens. Since then numbers have increased dramatically, with up to 30 000 animals now present in Melbourne. In 2003 the camp was moved to Yarra Bend. Melbourne is now an important area for this nationally vulnerable species. Seventeen species of insectivorous bat (85% of the Victorian species) occur in the greater Melbourne area, though rarely observed due to their small size (mostly 4-15 g) and cryptic nature. Some species are widespread throughout the suburbs, others found only in outer regions with significant areas of native vegetation. Most species roost in tree hollows, with some colonies using roofs of houses as alternatives.