The scope of this month's article is a little further afield than my usual central California locale, mainly because I'm doing my "research" sitting on a beautiful white sand beach on Oahu's windward shore. Lest you worry that this is a working vacation, let me assure you I'm also working on my tan and my snorkeling skills.
The history of the birdlife on Hawaii is a fascinating subject, and typifies the incredible changes brought by humans to these fragile ecosystems. The islands, formed as the Pacific Plate moved over a volcanic hot spot, are mere geologic infants. Kaua'i, the northernmost, and oldest island, is only five million years old, and Hawai'i (the Big Island), still forming as we speak, is only 1.5 million years old. So every plant, animal, and bird on the islands somehow found their way to those specks of rock in the middle of the Pacific Ocean, 2500 miles from the nearest continent, in that brief span of time.
The islands once supported 113 species of birds found nowhere else in the world. Because the only native mammal to Hawaii is a bat, and there were no native reptiles or amphibians, the birds were not predated upon on the ground, so flightless geese, ibis and rails evolved to fill that niche. The dominant herbivore on the islands was the Moa Nalo, a large flightless duck ancestor that weighed up to 17 pounds, and the top predators in the food chain were a harrier, a hawk, an eagle, and four species of owls . Today there are about 50 species of honeycreepers on Hawaii, and like Darwin's Finches, the first honeycreepers adapted to the incredible diversity of plant and insect life on the islands and evolved elaborate curved bills to sip the nectar of the island's tropical flowers, small warbler-like bills to eat insects, and large conical seed-eating bills, and the birds vary greatly in size and color and song.
Humans, doing what they do best — populating the planet — soon "discovered" the islands and quickly wrought dramatic changes. The early Polynesian settlers ate the Moa Nalo, killed the brightly colored honeycreepers for adornment, burned off the native forests to grow crops, and introduced pigs, dogs, and rats. That theme continued with the arrival of Captain Cook and the Europeans, and thus the Hawaiian bird populations have been forever affected by loss of habitat, and by the introduction of cattle, pigs, exotic plants, and mosquito-borne diseases. A rust disease threatens the most important food plants for the honeycreepers and plants are overwhelming the breeding habitat of the Black-footed and Laysan albatrosses. The mongoose, introduced to rid the islands of rats (brought to the islands on ships), are wreaking havoc on the ground nesting birds.
Japanese White-eye
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Because the island fauna evolved without these introduced predators, they are extremely vulnerable. In the list of bird extinctions worldwide, 87% have been on island archipelagos. About 58 species of Hawaiian birds have become extinct since the arrival of the first humans, and many more are endangered and threatened with extinction. Birds with impossible-sounding names such as O'o A'a, Nukupu'u, and the 'O'u, among others, are feared lost forever. In 1973, a bird new to science, the Po'o-uli was found in remote forests of Maui, and in 2005 the population numbered two individuals. Most of the Hawaiian Island's native birds are now only found above 5000 feet in elevation — the "mosquito line" — and it is feared that global climate change will allow the insects, and the avian malaria they carry, to populate the higher elevations, and rising sea levels will decimate the coastal breeding birds.
White-rumped Shama
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Among the land birds on the islands, nearly 70% now are introduced birds, epitomized perhaps by the Japanese White-eye. Introduced to the islands in 1929 for insect control, the white-eye was thought to be non-invasive, but it became quickly evident that was a wrong assumption. They are now considered a major threat to Hawaii's endemic birds, and range from sea level to the tree line on all the main islands, in both dry and wet habitats, and in native forests and suburban tracts. They have altered entire communities by spreading seeds of non-native plants, and are outcompeting the forest birds for food and nesting space in the old-growth forests. They nest in all but two months of the year, and can fledge three - four young in 10 days. They are very good at what they do.
The Hawaiian government and wildlife biologists are fighting back though, with increased acreage on wildlife preserves, and a constant vigilance towards thwarting the exotic introductions. With the state's constant influx of tourists from around the world, and the daily military flights onto the islands, it is a daunting task. Brown tree snakes were recently found at the Honolulu airport and military bases, no doubt a stowaway from Guam, where it is a serious bird predator. It will take a concerted effort to protect the remaining native plants and birds on Hawaii.
