For the Birds Radio Program: Planning a Trip to Hawaii
Hawaii Geology .
I’m planning a trip to Hawaii, and to understand the patterns of native birdlife there, I’ve been studying the island’s geology. Hawaii’s string of islands comprises one of the smallest states, totaling less than 17,000 square miles. The total land mass isn’t much smaller than Costa Rica’s, but while Costa Rica has over 830 species of birds, Hawaii has only 285. Over half of these are aliens, introduced by people from other places on the globe, and many of the others are migrants that fly in from the far north for the winter, such as Pacific Golden-Plovers and Northern Pintails. About 60 native Hawaiian birds have become extinct since the islands were first inhabited by humans, and more are in dire danger of extinction. There are only 45 species of forest birds endemic to Hawaii, and of these 15 are now extinct and several more are nearing extinction.
Only three Hawaiian crows remain, and a few forest species haven’t been recorded anywhere since the 1980s. But even if all the extinct birds still lived there along with all the exotics that we’ve introduced, Hawaii would still have considerably fewer species than Costa Rica.
Why does Hawaii have so few native birds? Costa Rica is right smack in the middle of two enormous continents-land masses both rich in birds. Costa Rica also borders two oceans, so its birdlife includes saltwater birds from two different seas. Hawaii is made up of islands in the middle of the ocean, a minimum of2400 miles from the nearest continent. And unlike Australia and New Zealand, at no time in geologic history was Hawaii attached to a continent. Rather, this string of islands was formed by volcanoes–you can actually watch the island of Hawaii grow as lava pours out of Kilauea, the most active volcano on the planet. Kilauea has spewed out more than two billion cubic yards of lava since 1983, and is still going strong.
The flowing lava of Hawaii’s volcanoes has buried enormous swaths of land, but because it doesn’t flow evenly, odd little pockets of vegetation remain between the fingers of hardened lava-these are called kipukas and in the higher elevations are excellent places to see native Hawaiian forest birds. As lava cools, the first plants to invade were virtually always the red flowered, beautiful ohia-lehua trees. These pioneers break up the lava, and then provide shade for other plants. Because they pioneered right as the lava cooled, large stands of ohia trees are virtually all the same age, and in many cases all seem to die at once. When the island was undisturbed newer ohia plants took over as the older generation died, but now in many cases introduced weeds become the new climax vegetation, which is good for introduced birds but bad for the native birds that depend on the native ohia trees and the mix of natural Hawaiian vegetation.
Hawaii had few natural freshwater wetlands to begin with, and thanks to agriculture and settlement, most of these have been drained. What is now Pearl Harbor and Waikiki were once all wetland. But there are still pockets of wetland and man-made ponds that provide some habitat for freshwater birds. Once bazillions of oceanic birds nested on all the islands, but virtually all have disappeared from the main islands now.
Only two mammals reached Hawaiian shores on their own-the Hawaiian Bat flew and the Hawaiian Monk Seal swam there-and there are no native reptiles or amphibians. But if Hawaii’s native birds are few in number, they make up for it in quality. Next time I’ll tell you about some of the most fascinating species.