A small population of South Island brown kiwis lives in the north of the Haast range as well as in the Arawhata and Waiototo valleys at the foot of the ranges. Paradise shelducks are common in grassy flats, while the numbers of blue ducks, who live in torrents, are decreasing. Riverbeds are habitats for migratory and wading birds such as wrybills, pied stilts, arctic terns, pied oystercatchers, dotterels and black-billed gulls. See also Birds of New Zealand . Both New Zealand's only native mammals, the long and short-tailed bats, live within the park.
Insect life is rich, including beetles, moths, flies, grasshoppers, and wetas.
The giant carnivorous snail Powelliphanta lives in the Haast river area. Native galaxiid fish can be found in many parts of the park, and especially in the rivers of the western side, where they sustain commercial whitebait fishing. Introduced animals have had a destructive impact on both native flora and fauna in Mt Aspiring National Park, as in many other parts of New Zealand. Rats, cats and mustelids are responsible for the decline in numbers of many bird, insect and reptile species. Red deer were introduced from 1871 until the 1920s to provide game for hunting.