Unusual birds show up in Hawai'i every year, and this year's prize find is a white-tailed eagle that has been soaring Kaua'i's mountains since December.

The animal appears to be a mature bird, and is making itself comfortable, said Bob Dieli, an outdoor recreation planner with the Kilauea Point National Wildlife Refuge.

"It has been seen at Waimea, Makaha (Ridge), and along the mountains behind Kapa'a, too. But most of the time it's from Larson's Beach to Kilauea" on the island's northeastern shore, he said.

The eagles feed on birds, fish and occasionally small mammals. Among its prey: Laysan albatross nesting along the coastline. With a wingspan that can be 6 to 8 feet, it is the only bird in the Kaua'i environment bigger than a Laysan albatross.

Dieli said that while albatross are protected, they are far more common than white-tailed eagles, so no one is planning to remove the eagle to protect the seabirds. Wildlife officials hope the eagle gets a taste for feral chickens that have overrun Kaua'i.

The eagle's presence on Kaua'i has fascinated birders, and even after four months, "we still get people asking about it," he said.

The white-tailed eagle or white-tailed sea eagle, Haliaeetus albicilla, has a home terrain from Northern Europe across northern Asia to the Aleutians. This tree-nester is closely related to the American bald eagle, which also has a white tail.

And it's not the first white-tailed eagle to inhabit Hawai'i.

Smithsonian Institution fossil bird expert Storrs Olson said scientists have found fossil eagle bones on Moloka'i, O'ahu and Maui. The bones of the bald eagle and sea eagle are so similar that he couldn't tell them apart. But Olson said his team was able to extract DNA from a Maui bird that lived 3,300 years ago. It was the same species as the Kaua'i eagle.

"The living bird now on Kaua'i is of great interest in showing that the birds obviously could get to the (Hawaiian) archipelago from the Asian mainland and also that Kaua'i would be the most obvious landfall coming from that direction," Olson said in an e-mail.

But oddly, researchers have never found eagle bones in Kaua'i fossil deposits.

"This is a complete mystery to me, as eagles would easily be capable of flying from O'ahu to Kaua'i," Olson said. "We have never found any eagle bones on the Big Island but that doesn't mean anything because our fossil record from there is so incomplete."

If you have a question or concern about the Hawaiian environment, drop a note to Jan TenBruggencate at P.O. Box 524, Lihu'e, HI 96766 or jant@honoluluadvertiser.com. Or call him at (808) 245-3074.