Evolving in the remote Hawaiian Archipelago and having the smallest range of any living goose, the Hawaiian Goose, or better known by its Hawaiian name—Nënë, is among the most isolated, sedentary, and threatened of waterfowl. The Nënë is also highly terrestrial, and several structural features demonstrate its adaptation to life on islands with limited freshwater habitat: It stands taller and more upright than geese of similar weight, enabling it to reach high to browse the fruits, seeds, and foliage that constitute its herbivorous diet; its legs and padded toes are long and strong, promoting swift, sure walking and running over rugged terrain; webbing is reduced between the toes; and though it is a capable swimmer and readily uses freshwater habitats when available, the Nënë does not require freshwater or oceanic habitats in the same way that many other waterfowl do.
Nënë were once widely distributed among the main Hawaiian islands; although they are capable of interisland flight, their wings are reduced in size, and they do not migrate from the archipelago. Although little is known about the vegetation structure and composition of habitats used by Nënë before human colonization and alteration of ecosystems, especially in the lowlands, Nënë seem adaptable and use shrublands and grasslands and human-altered habitats ranging from coastal to subalpine environments. Their distribution during the historic period (after 1778) reflects only a portion of the range that fossil remains indicate this species once occupied. Nevertheless, on the younger, larger, and southernmost islands of Hawai‘i and Maui, Nënë nest, raise their young, forage, and molt in grassy shrublands and sparsely vegetated lava flows. Some populations formerly moved seasonally from montane foraging grounds to low-land nesting areas. On Kaua‘i Island, Nënë inhabit mainly lowland pastures and other modified habitats.
Like other insular waterfowl, Nënë lay relatively large eggs in small clutches during an extended nesting season. Although pairs may renest after losing their first brood, gosling growth is slow and survival is low in mid- and high-elevation nesting areas, where habitat conditions are often marginal. Productivity is low on Hawai‘i and Maui Islands because diets of birds in wild habitats are limited by insufficient protein intake, and introduced mammals destroy many nests. Productivity is higher, however, on Kaua‘i Island where nutritious food is readily available in managed grasslands and where there are fewer predators. Adults and young forage on a wide range of native and introduced grasses, shrubs, and forbs, but highly nutritious foods are not readily available in remnant natural habitats, and Nënë populations survive and grow where managed grasslands or supplemental food are available. Nënë evolved with aerial predators, most of which are now extinct, but several introduced mammals now prey on these ground-nesting geese.
The Nënë is 1 of at least 11 species of waterfowl to have evolved in the Hawaiian Islands. The endemic Hawaiian anatids, at least 8 of which are extinct and known only from fossil remains, represent the most unusual assemblage of waterfowl anywhere because most were flightless and many were also terrestrial, herbivorous, gooselike derivatives of ducks or ancestors of uncertain affinity. Only the Nënë, Hawaiian Duck (Anas wyvilliana), and Laysan Duck (A. laysanensis) survive, although all are listed by the U.S. Fish and Wildlife Service and the state of Hawai‘i as Endangered Species. The Nënë's closest living relative is the Canada Goose (Branta canadensis).
Although quite adaptable in its diet and use of habitats, the Nënë nearly became extinct in the 1950s. Its subsequent rescue is a classic case study in the management of endangered species. Efforts in England and the Hawaiian Islands to propagate Nënë in captivity and release young to the wild have inspired similar projects around the world. Nonetheless, substantial additional efforts to reduce threats from predators and to enhance foraging opportunities by improving habitat conditions are needed if the Nënë is to recover fully.