HONOLULU — On Polynesian voyaging routes, people long have read the arrival of birds as a cue to the presence of land. In modern Honolulu, white terns—known locally as manu-o-Kū—have become a recurring sight in that same city landscape, with new counts and survey results pointing to a population that has expanded even as many other native birds in Hawaii declined.
Kaʻiulani Murphy, who guides Polynesian voyaging canoes, said she has long been quick to spot the white terns flapping their wings as the vessels move across the Pacific. She described how the birds hunt for food at sea and lay eggs on land, a pattern that can signal to traditional navigators that land is near.
The latest reporting ties the growth to multiple layers of monitoring. Hui Manu-o-Kū, the volunteer group that tracks the birds, said it had 691 eggs and chicks in Honolulu trees “as of this week,” and the group’s work is tied to the Hawaiian name for the white tern, manu-o-Kū, meaning “bird of Kū,” the god of war.
Scientists and conservationists also point to wider trends in how the birds are breeding on Oahu. New data described in the reporting says the white tern population in Honolulu has jumped more than 50% in the past decade, and the group’s most recent population survey, conducted in 2023 but unpublished until now, found Oahu’s population of breeding adults rose 1.5 times to 3,600 compared with 2016.
The birds’ success stands out against the broader picture of Hawaii’s native bird declines after humans arrived and introduced predators and diseases. The reporting said that since humans came to Hawaii, 71 of 113 bird species found only on the islands have gone extinct, and that many of those remaining are threatened or endangered, often living in smaller numbers in higher-elevation forests.
White terns are native to the islands, but they were not observed breeding on Oahu until 1961, when scientists saw a pair of adults with a single egg. Decades later, as the bird population grew, Honolulu named manu-o-Kū its official bird in 2007, with school children singing songs about the species and an annual festival held every May.
Part of the reason the birds fit into the city may involve where they choose to lay eggs. The reporting said the terns do not build nests and instead lay eggs on bare tree branches, cliff ledges or even window sills; after hatching, the young remain on a branch until they can fly, with strong claws that help them hold on during strong storms.
In Honolulu, Hui Manu-o-Kū staff help reduce conflicts between the birds and routine tree care. The group ties blue plastic ribbons around trunks of trees that host eggs and chicks to alert tree trimmers to stay clear, and it also uses an online map to help bird-watchers track the birds. Joyce Hsieh, who has taken photos of the terns for eight years as they incubate eggs, feed young birds and raise hatchlings, said one of her preferred spots is a Target parking garage because she can reach the same height as birds in nearby trees.
For researchers, the central question remains why this seabird is thriving in the urban core. The reporting said scientists are not sure, but suggested several possible explanations, including that the city may be more hospitable because humans have reduced predators such as rats and cats around restaurants and buildings. The reporting also pointed to busy roads deterring predators and said that barn owls and mongoose, other species that feed on terns, are rare in the urban core.
Eric VanderWerf, executive director of Pacific Rim Conservation, said the birds appear undisturbed by city life. “All the lights and the noise, the commotion of people and traffic, and things like that, doesn’t seem to bother them,” VanderWerf said.
The reporting also described how even small habitat details can matter, with downtown trees providing favorable places for eggs. It said that a cup made from the scar tissue of a trimmed tree branch can be an ideal spot for an egg, and that well-maintained trees can therefore create plentiful homes for the breeding birds.
Murphy, the traditional voyager, linked the birds’ presence to a sense of continuity and resilience, drawing parallels between the birds’ adaptation and her people’s history. She said diseases introduced by the first Europeans killed Native Hawaiians in vast numbers in the 1800s, but that Hawaiians remain and their population is growing; she described seeing terns offshore en route to Oahu as “like seeing old friends,” adding, “It’s just a special feeling.”