Hawaiian Birds and Hawaiian Honeycreepers
Smithsonian scientists have determined the evolutionary family tree for one of the most strikingly diverse and endangered bird families in the world – the Hawaiian Honeycreepers. The researchers determined the types of finches that the honeycreeper family originally evolved from and also linked the timing of that rapid evolution to the formation of the main Hawaiian Islands. Using genetic data from 28 bird species that seemed similar to the honeycreepers morphologically, genetically or that shared geographic proximity, it was determined that the various honeycreeper species evolved from Eurasian rosefinches.
There were once more than 55 species of these colorful songbirds, and they are so diverse that historically it wasn’t even entirely clear that they were all part of the same group. Honeycreepers probably represent the most impressive example of an adaptive radiation in vertebrates that has led to a number of beak shapes unique among birds. Some eat seeds, some eat fruit, some eat snails, some eat nectar. Some have the bills of parrots, others of warblers, while some are finch-like and others have straight, thin bills.
Hawaii’s unusual geology played a role in the rapid evolution of many honeycreeper species that followed. The volcanic islands have formed one by one over time, as the Pacific tectonic plate is dragged across a “hot spot” of magma, and each new island provided a new opportunity for colonization. Each island that forms represents a blank slate for evolution, so as one honeycreeper species moves from one island to a new island, those birds encounter new habitat and ecological niches that may force them to adapt and branch off into distinct species.
The researchers looked at the evolution of the Hawaiian honeycreepers after the formation of Kauai-Niihau, Oahu, Maui-Nui and Hawaii. The largest burst of evolution into new species, called a radiation, occurred between 4 million and 2.5 million years ago, after Kauai-Niihau and Oahu formed but before the remaining two large islands existed, and resulted in the evolution of six of 10 distinct groups of species characterized by different sizes, shapes and colors.
Kauai History and Hotspot Theory
At one time or another we have all heard the theory of plate tectonics, in which the Earth’s surface consists of about a dozen rigid slabs or plates, each averaging at least 50 miles thick. These plates move relative to one another at average speeds of a few inches per year. The great majority of the world’s earthquakes and active volcanoes occur near the boundaries of the Earth’s shifting plates.
Why then are the Hawaiian volcanoes located near the middle of the Pacific Plate more than 2,000 miles from the nearest plate boundary?
Enter the ‘hotspot theory’. According to the hotspot theory, the Hawaiian Island chain resulted from the Pacific Plate moving over a deep, stationary hotspot in the mantle, located beneath the present-day position of the Big Island. Heat from this hotspot is producing a persistent source of magma by partly melting the overriding Pacific Plate. The magma then rises through the mantle and crust to erupt onto the sea floor, forming an active seamount. Over time, countless eruptions cause the seamount to grow until it finally emerges above sea level to form an island volcano. As the plate movement carries the island beyond the hotspot, the magma source is cutoff, leaving one island volcano extinct, and another waiting to develop over the hotspot. This trail of volcanic islands and seamounts can be seen across the Pacific Ocean floor.
The State of Hawaii is composed of 132 islands, reefs and shoals that extend for over 1500 miles across the central North Pacific Ocean from the Big Island to Midway and Kure Atolls. Included in this chain are some of the Earth’s largest mountains, rising 18,000 feet from the ocean bottom to a height above sea level of nearly 14,000 feet. Mauna Kea and Mauna Loa on the Big Island are volcanic mountains with a total elevation of nearly 32,000 feet.
next – Kauai History and Volcano Islands
