Friday, November 7, 2014
Bird of the Day: What Happens if a Canada Goose goes on a Tropical Vacation? nene!
During the millennia that followed, different flocks of geese took up residence in different ecological niches, such as lava flows, grassy slopes, and woodlands. Isolated groups began to diverge, and before long at least three species developed on the islands. One of them, the Giant Hawaiian Goose (species name not yet established), was big, almost four feet long. A lack of predators on the island made flight an energy-intensive but unneeded luxury, so the wings became smaller as the bird evolved to larger size. The goose was flightless. This worked fine for a long time, but humans ultimately arrived on the islands, and probably exterminated them, either by hunting, or by introduction of egg-eating rats, or by habitat destruction.
The second species was the nene-nui (Branta hylobadistes). It was also a big bird, but had larger wings so that it was still capable of weak flight. Like the Giant Hawaiian Goose, it became extinct soon after the arrival of humans on the islands. It has been characterized as a bird in evolutionary transition, in the midst of losing the ability to fly, but it went extinct first. Possibly because it couldn't fly well.
The flying goose, the one that survived was the nene (Branta sandvicensis). The nene's wings were smaller than its Canadian ancestors, because it didn't need to migrate thousands of miles during the change of seasons. But it retained enough flying ability to escape from the island's human invaders. It differed from the Canada Goose in several other respects, including longer legs, reduced webbing between its toes, and a more erect posture. It is adapted to living on lava flows and grasslands, and was less dependent on wetlands than other geese.
It survived, but no longer thrived. Rats ate their eggs and chicks, and later on cats and mongooses were brought to the islands. The species was devastated, dropping from an estimated 25,000 when first European contact was made in 1778 to thirty individuals in 1952. A captive breeding program began, and populations were established on their ancient habitats on Maui and Kauai (where mongooses were never introduced). The wild population is now around 800, with another thousand or so in captivity. They are still highly endangered, but their prospects are slowly improving. They have been named the state bird of Hawaii.
Are you interested in learning a bit more about these fascinating creatures? Here is a link for a National Geographic article on the evolution of the Hawaiian geese and their Canadian cousins, and the scholarly article of the research into the vanished species: