Nuuanu resident Robert emailed, “For the last few years we have been blessed by beautiful white birds cavorting in the sky, swooping all over our valley at great speed. They never seem to go to ground, although they have settled for a few minutes in some tall trees around our home. They seem to be having a blast! Do you know what they are and why they swoop back and forth?”

Any Oahu resident who writes about being blessed with beautiful, white birds that race about and land in trees can mean only one species: the white tern or manu-o-Ku, formerly known as the fairy tern. White terns are foot-long seabirds with 30-inch wingspans which can hover over the ocean’s surface while plucking out fish. The birds also helicopter close overhead to check out a person and soar like Captain America’s buddy Falcon.

Fairy terns have a circle of black feathers around their eyes, giving them a mild-mannered and lovable look. Usually they are. But threaten them and the charming terns become the original angry birds.

At Midway Atoll last year, I saw hundreds of white terns gang up on a peregrine falcon that got blown to the atoll. In a raucous mob high above the trees, the sweet-looking terns shrieked, pecked and dive-bombed the poor peregrine until it flew off. Having nowhere else to go, however, the little raptor later returned to the island, once again unleashing the fury of the white angels.

Although white terns are abundant in the Northwestern Hawaiian islands, in the main islands they breed only on Oahu. In 1971 the first pairs were seen in Kapiolani Park and Fort DeRussy. The birds continued to branch out in the 1980s, raising chicks in downtown Honolulu, Pearl City and Nuuanu Valley. In 2002 a researcher counted 500 breeding terns in the city and suburbs. (They don’t seem to like the countryside.) Today estimates of white terns on Oahu are around 1,600.

The cavorting that Robert describes could be mating displays or prospective parents looking for a place to raise a chick.

White terns make no nest whatsoever. The female lays her egg in the crook of a tree branch or on a bare rocky ledge. If the parents choose a site that holds their egg through incubation and hatching, and the chick balances there well enough to fledge, that family wins the natural selection award.

Robert sent two pictures of his birds in flight, confirming my guess that his swoopers are white terns. How lucky we are that the fairylike birds have chosen our island to enchant. You can find white terns at Kapiolani Park, Fort DeRussy, Iolani Palace, Thomas Square, Foster Botanical Garden and some Windward communities as the birds continue expanding their range.

Reach Susan Scott at susanscott.net.