The appearance this year of an eagle on Kaua'i, an osprey on O'ahu, a harrier on Maui, and reports of peregrine falcons on several islands suggests either that there's something strange going on, or that visits by these Mainland birds are far more common than most folks know.

Bird watchers regularly make note of the appearance of unusual birds in the Hawaiian environment, and it suggests that the 2,000-plus-mile passage from almost anywhere to Hawai'i is not as daunting for many forms of avian life as it might appear.

Tiny shorebirds do it annually. The kolea, or Pacific golden plover, among the Islands' most beloved snowbirds, left Hawai'i about a month ago for their summer breeding season in the Arctic. They'll be back in the late summer and fall, to spend winter where it's warmer.

Waterbirds like mallards show up with some frequency, although their feats might not be considered quite so impressive, since their swimming ability means they could stop on the ocean for a break along the way.

Most raptors aren't regular cross-ocean migrators, and many are not able to land on the water and then take off again.

But they make the crossing, and it's not a new thing. Fossil evidence of prehistoric eagles on O'ahu and Maui County shows they were here before humans were.

Kaua'i's famous golden eagle arrived unannounced and was on the island throughout the 1970s, until it was killed while attacking a helicopter in 1984.

George Balazs, who is best known for his studies of Hawaiian green sea turtles, reported a Steller's sea eagle in 1978 on Kure Atoll, on the northwesternmost end of the Hawaiian archipelago. A month later, a similar-looking eagle, and perhaps the same one, was on Midway, 60 miles east of Kure.

In December 2006, "we believe that we had probably two peregrine falcons pass through Midway," said John Klavitter, U.S. Fish and Wildlife Refuge biologist at the Midway Atoll National Wildlife Refuge. Both preyed on Laysan ducks that have been brought to Midway to establish a breeding population.

One of those birds may have moved down the Hawaiian chain, since one was spotted at Laysan Island later in December. What's not known is whether it was the same peregrine that was reported early this year on Kaua'i.

Klavitter said he believes peregine falcons show up at a rate of one or two a year at Midway.

Not surprising, perhaps, since peregrine means "wandering" or "nomadic."

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.