The Hawaiian archipelago is a chain of volcanic islands located in the central North Pacific Ocean, making it the most geographically isolated major landmass on Earth. Situated nearly 2,400 miles from the nearest continent, this extreme remoteness created a unique evolutionary laboratory for the life that successfully crossed the vast ocean. Hawaiian wildlife is sharply divided between the rare, unique species that evolved there and the abundant animals that have been introduced by humans.
Endemism: Why Hawaiian Wildlife Is Unique
The defining characteristic of Hawaiian wildlife is its high degree of endemism, meaning species are found nowhere else on Earth. Roughly 90% of the native terrestrial species in Hawaii are endemic, a direct result of the islands’ isolation. Colonization happened rarely, primarily by what is often summarized as the “three Ws”: wind, waves, and wings.
Species that arrived, such as the ancestors of birds, insects, and plants, were few in number and often represented a single “founder species.” Once established, these founder populations underwent adaptive radiation. This evolutionary phenomenon allowed a single ancestral species to rapidly diversify into numerous new species, each adapted to a specific ecological niche or island habitat.
The archipelago’s diverse ecological zones, ranging from rainforests to alpine deserts, provided many open niches for these new species to fill. This process created distinct species on different islands, allowing a single lineage to diversify into many forms across the chain. However, the high rate of speciation meant that these endemic species evolved without the natural defenses against predators, diseases, and competitors common on continents.
Defining Marine and Coastal Wildlife
The ocean surrounding Hawaii supports a variety of marine and coastal species, many of which are endemic. One unique example is the Hawaiian Monk Seal (Monachus schauinslandi), one of the world’s most endangered seal species and the only seal native to the United States. Known in Hawaiian as ʻIlio holo i ka uaua (“dog that runs in rough water”), these seals are often seen resting on secluded beaches across the islands.
The Green Sea Turtle (Chelonia mydas), known locally as Honu, is a common sight in nearshore waters, frequently grazing on marine plants. These large reptiles are considered a form of ʻaumakua, or family guardian, in Hawaiian culture and are federally protected. Humpback Whales (Megaptera novaeangliae), or Kohola, are seasonal visitors, migrating thousands of miles from northern feeding grounds to the protected waters of Hawaii each winter to mate and calve.
Closer to the coral reefs, over 700 species of reef fish thrive, with about 25% being endemic. The state fish, the reef triggerfish, known by its long Hawaiian name, Humuhumunukunukuāpuaʻa (Rhinecanthus rectangulus), is one of the most recognizable examples. This brightly patterned fish uses its sharp spine to lock itself into crevices for protection.
Endemic Terrestrial Fauna (Birds and Bats)
The terrestrial environment is home to specialized native animals, particularly birds and invertebrates. The Hawaiian honeycreepers are perhaps the most famous example of adaptive radiation, with over 55 known species having evolved from a single ancestral finch. These birds exhibit a spectacular range of bill shapes, specialized for different diets, such as the curved bill of the ʻIʻiwi used to sip nectar from native flowers.
The Nēnē (Branta sandvicensis), or Hawaiian Goose, is the state bird and an endemic species believed to have evolved from the Canada Goose. Unlike its mainland relatives, the Nēnē is non-migratory and has adapted to walking across lava flows and rough terrain, reflected in its reduced webbing on its feet. The islands’ sole native land mammal is the Hawaiian Hoary Bat (Lasiurus semotus), or ʻŌpeʻapeʻa, a subspecies of the North American Hoary Bat. This bat is a nocturnal hunter found across the islands.
Native invertebrates also display unique characteristics, such as the tiny Happy Face Spider (Theridion grallator), found on several main islands. This small, non-venomous spider is famous for the distinct, smiley-face-like pattern on its abdomen. The color polymorphism of the markings suggests they may serve as a defense mechanism to deter predators like birds.
Pervasive Introduced Species
A significant portion of the terrestrial wildlife encountered daily consists of animals brought to the islands by humans, either intentionally or accidentally. These non-native species often thrive in the absence of natural predators, posing a major threat to the fragile endemic ecosystem. One widespread introduced mammal is the Small Indian Mongoose (Herpestes auropunctatus), brought in the late 19th century to control rat populations in sugar cane fields.
This effort was unsuccessful because the mongoose is diurnal while the rats are largely nocturnal, leading the mongoose to prey heavily on native, ground-nesting birds and their eggs. Feral pigs (Sus scrofa), or puaʻa, were introduced by early Polynesians and later by Europeans. They cause extensive damage by rooting up native plants and creating wallows that serve as breeding grounds for disease-carrying mosquitoes. The Axis Deer (Axis axis) was introduced for sport hunting and has rapidly multiplied on islands like Maui and Molokaʻi, causing significant damage to vegetation through overgrazing.
Commonly seen introduced species include the Coqui frog (Eleutherodactylus coqui) from Puerto Rico, known for its extremely loud, high-pitched nocturnal call that can reach over 90 decibels. Introduced birds like the Common Mynah (Acridotheres tristis) and various species of cardinals are now abundant in urban and low-elevation areas. These non-native species represent the most common wildlife encounters for visitors and residents, contrasting sharply with the elusive native fauna found in protected forests.