Hawai'i's national wildlife refuges are reporting a number of unusual visitors this year, some seen here for the first time.

They include the Nazca booby, which landed in July at Tern Island in the Hawaiian Islands National Wildlife Refuge, and an American avocet, similar to a Hawaiian stilt, spotted last month at the Kealia Pond National Wildlife Refuge on Maui. Both birds had never been observed before in the Islands.

Kealia also attracted a marbled godwit, a large seabird known as "accidental stragglers" to Hawai'i but rarely seen.

"Our national wildlife refuges in the Pacific are often small remnants of wetland habitats or tiny islets and reefs in the midst of a vast ocean, but that makes them all the more important to migratory birds," said Barry Stieglitz, project leader for the U.S. Fish & Wildlife Service's Pacific island refuges. "Our proverbial welcome mat is always out for wildlife, but it's particularly exciting to see new species find these special places."

Hawai'i's wetland refuges report unusual arrivals almost every year, according to Beth Flint, a Fish & Wildlife biologist. In most cases, the birds were blown off course or became disoriented, but in some cases, Flint said, their presence is a sign of some sort of ecological phenomena, such as warmer ocean water intruding north or colder water spreading into southern seas.

"Usually it's just a case of bad luck on the part of the bird," she said.

Bad luck because many of the out-of-place arrivals end up starving to death, unable to pursue their usual diet or to survive the long flight back to familiar territory, Flint said.

Of this year's visitors, Flint found more interesting the appearance of the American avocet and the marbled godwit. "It's more challenging for them to get all the way to Hawai'i. They don't forage at sea and had to make a very long flight without feeding," she said.

By comparison, seabirds such as the Nazca booby "have an enormous capacity for flying over the ocean and foraging at sea."

There are nine national wildlife refuges in the main Hawaiian Islands, seven of them featuring wetlands for migratory species and native waterbirds. Their usual inhabitants include the Hawaiian stilt (ae'o), coot ('alae ke'oke'o), moorhen ('alae 'ula), and duck (koloa). Although endangered, these birds are common sights at the refuges.

Longtime bird-watching enthusiast Ron Walker of Kane'ohe didn't observe any of this year's unusual visitors, but the off chance of spotting a species not usually found in Hawai'i is what compels Walker and others to return to wetland sites with their notebooks and binoculars.

"In Hawai'i, the native, nonmigratory birds are pretty well-known, and the number of species is fairly limited compared to a place like the California Central Valley," Walker said. "So when a bird like the American avocet comes to Hawai'i, that's big news."

The American avocet, which made an appearance in September at the Kealia Pond refuge, is similar to the Hawaiian stilt but larger. It normally winters along the coasts of Mexico, California and the southeastern United States. Their summer breeding range is mostly in the western Great Plains.

"This sighting created quite a stir in the birding community," said Kealia refuge manager Glynnis Nakai.

Outside of breeding season, the American avocet has a grayish head, neck and chest, but during breeding season, the gray turns to a soft rust color. Its most distinctive feature is a long upturned bill, which it swings through shallow water to catch small invertebrates.

Also taking up temporary residence at Kealia was a marbled godwit, which stayed on Maui from January to April before flying to O'ahu, where it was sighted May 9 at the James Campbell National Wildlife Refuge.

It was the first sighting of a marbled godwit at the Kahuku refuge, and at last report, the bird was still in residence. The species typically winters along the coastlines of the United States and Mexico. It is a rich cinnamon brown with a distinctive, slightly upturned bill with a dark tip and pink base.

The Nazca booby, commonly found in the Galapagos Islands and on Malpelo Island in Colombia, occasionally strays to the California coast, but scientists were surprised to hear from volunteer Linda Takahashi that one had landed at Tern Island, staying for more than two weeks before flying off in early August.

Like its cousin the masked booby, Nazca boobies are all white with black on the edges of their wings and tail. But instead of a yellow bill, this species has a more tapered, bright orange bill.

A curlew sandpiper, a Eurasian species rarely seen in Hawai'i, also is believed to have done some island hopping, landing at Kealia in January and in May moving on to the Campbell refuge, where a second curlew sandpiper was seen. This medium-sized sandpiper nests on tundra and occasionally migrates to the East Coast but is rare on the West Coast.

The Pearl Harbor National Wildlife Refuge welcomed its first white-faced ibis during the winter, and a second, younger bird arrived last week at the Campbell wetlands. Normally this species winters in southern California, southern Texas, southern Louisiana and Mexico. This dark wading bird has a long, down-curved bill.

Other unusual refuge visitors this year include a peregrine falcon, osprey, a greater white-fronted goose, cackling geese and a tufted duck.

Walker said more unusual winter sightings are likely.

"For people like myself who do a lot of birding, we look forward to the winter months when you get these oddball migratory birds and waterfowl that aren't here all year round," he said.

Reach Christie Wilson at cwilson@honoluluadvertiser.com.