Manu-o-Kū – White-Tern
Gygis alba
| Stated-recognized | Indigenous |
| NatureServe Heritage Rank | G4 – Apparently Secure |
| North American Waterbird Conservation Plan |
Moderate Concern |
| Regional Seabird Conservation Plan |
USFWS 2005 |
The Manu-o-Kū, or White Tern, is a small, all-white bird belonging to the family Laridae, found in tropical regions around the world. These terns have dark eyes and a thick, sharply pointed black bill with an electric blue base. Adult males and females look identical, and there are no seasonal changes in their plumage.
The flight of the Manu-o-Kū is buoyant, characterized by erratic changes in direction and speed. They feed by dipping their beaks into the water’s surface or by diving. White Terns often join hunting parties made up of several bird species and primarily prey on fish that have been driven to the surface by larger predatory fish. In Hawai‘i, their diet consists mainly of juvenile goatfish and flying fish.
Breeding adults stay close to their nesting sites and forage in inshore areas, such as shoals and banks, occasionally venturing into offshore waters. Unlike most other terns, the Manu-o-Kū is not very colonial or social, preferring to nest either in loosely associated groups or alone. They usually remain paired for multiple breeding seasons and often return to the same nesting site year after year.
Instead of building nests, a single egg is laid in a suitable depression found on tree branches, buildings, man-made structures, rock ledges, or on the ground. In Hawai‘i, White Terns breed year-round, although most eggs are laid between February and June. If their first nesting attempt fails, pairs will replace the egg, and some can successfully raise two or three sets of offspring each year. Both parents share the responsibility of incubating the egg, brooding, and feeding the chick.
Newly fledged birds rely on their parents for up to two months. They typically start breeding at about five years of age, and the oldest known individual lived to be 42 years old.
The Manu-o-Kū (White Tern) breeds throughout the Northwest Hawaiian Islands (NWHI) and on the island of Oʻahu. Outside of Hawaiʻi, these birds also breed on islands in subtropical and tropical oceans, although their breeding in the southern Atlantic Ocean is limited. The non-breeding distribution of the Manu-o-Kū is not well understood. Typically, they remain near their breeding colonies year-round and seldom venture far from shore.
The Manu-o-Kū breeds on oceanic islands, including low-lying coralline sand islands and high volcanic islands. They do not build nests; instead, eggs are laid in any suitable depression available. Common nesting sites include volcanic pinnacles, cliffs, rocky slopes, large bushes or trees, and man-made structures. They are often seen foraging in nearshore waters.
The following management goals are important to Pacific seabird conservation: maintain, protect, and enhance habitat; eradicate or control non-natives; minimize bycatch and other negative effects of fishing; improve the effectiveness of oil spill response efforts; identify contaminates and hazardous substances; and minimize the effects of powerlines, towers, wind turbines and lights (USFWS 2005). The goal of these management actions is not only to protect seabird populations and their breeding colonies, but also to re- establish former breeding colonies thereby reducing the risk of extinction. In addition to these efforts, future management specific to Hawaiian populations of Manu-o-Kū (White Tern) should include the following:
Eradication and control of introduced predators at current and potential nesting sites. Continued protection and management of existing wildlife sanctuaries and refuges.
Like all seabirds, both adult White Terns (Manu-o-Kū) and their nests are vulnerable to predation by rats (Rattus spp.) and feral cats (Felis silvestris). However, all sites in the Northwestern Hawaiian Islands (NWHI) are free of these predators. Due to the remote nature of their nesting sites, which often include cliffs, Manu-o-Kū are less susceptible to predation compared to many other seabird species. Historically, rats have likely preyed on eggs, chicks, and adult birds on Midway Atoll.
Hui Manu-o-Kū
The Hui Manu-o-Kū is a group of dedicated conservationists and citizens who have come together to observe, protect and raise awareness about Manu-o-Kū. Noting that very little focus was being put on the official bird of Honolulu, the group was formed in 2016. This is a collaborative group with representatives from US Fish and Wildlife Service, Pacific Rim Conservation, Hawaii Audubon Society, ‘Iolani School, State of Hawaii Department of Land and Natural Resources, Hawai’i Wildlife Center, and public citizens. We all share dedication and compassion for these beautiful native Hawaiian seabirds.
