The animals were very similar to the extant hippopotamus and pygmy hippopotamus. The pygmy hippo is reclusive and nocturnal. Brown-mantled tamarins are generally sympatric with pygmy marmosets and often raid pygmy marmosets' gum holes. Nomenclature of the pygmy hippopotamus reflects that of the hippopotamus. Several folktales have been collected about the pygmy hippopotamus. Young pygmy hippos can swim almost immediately. This moth species is the preferred food source of mountain pygmy possums. Visitors include pilot whales and pygmy sperm whales. The gestation period of pygmy rabbits is unknown. Even large animals such as birds, bats, and pygmy possums can be employed. The reproduction of pygmy three-toed sloths is unknown. The programme cared for a population of 45 mountain pygmy possums. Few reliable estimates exist for population status of pygmy blue whales. It seems to prefer warmer waters than the pygmy sperm whale. A breeding pair of pygmy right whales were retained in a netted area.