Sunday, September 20, 2015

Land of the Lost: The Nene of Hawai'i

For the first-time traveler to Hawai'i, a word about the birds. There are two groups of birds, the species native to the Hawaiian Islands, and the introduced, or invasive species. There are also two groups of birds, the ones you are likely to see during your trip, and the ones you won't. It's unfortunate, but the two lists are pretty much the same. The native birds of the islands are under assault, and most of them never were a good fit for urban environments where island visitors spend most of their time. The natives have been decimated by disease (often transmitted by mosquito, another island invasive), habitat loss, predation by rats, mongoose, and cats, hunting, and competition from non-native birds. The state bird of Hawai'i, the nene (Branta sandvicensis), is the most iconic example of a native that was almost driven to extinction. A close relative, the Giant Hawaiian Goose, once lived on the island, but is now extinct. I wrote about the nene a few months ago, and the following is an abridged version of that post.

Perhaps 500,000 years ago, a pregnant Canada Goose, or a small flock of geese took a wrong turn. A really wrong turn. Somehow, flying along the coast of North America, the leader maybe decided to take a short cut, and it went poorly. Soon the shoreline was lost to view, and for days, not a single bit of land could be seen. I can imagine the flock becoming smaller and smaller as the weaker members fell behind and were lost.  After days of nothing but ocean, an island came into view. The tired geese landed and began looking for food. None of the plants were particularly familiar, but some proved edible and a few of the geese survived. For all we know, some of them rested up and left for further journeys, but a few stayed around. They took up residence on the volcanic island in the tropics of the Pacific Ocean, a vastly different environment than their summer home in the Canadian Arctic. The isolated volcanic edifices are today called the Hawaiian Islands.

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.
I didn't mean that as a flippant remark. Evolution is a process that has provided the incredible diversity on our planet, and isolated islands have provided the crucible in which much of the planet's diversity has arisen. But birds and other animals that have adapted to very specific situations are vulnerable when those situations are changed. The two extinct Hawaiian geese species were secure on the Hawaiian Islands, but the arrival of humans changed their environment too much and too fast. They were certainly easier to capture than a bird that could escape by flying.

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 1,950 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.
I've seen the nenes (pronounced "nay-nay") on Maui at Hosner Grove (the top picture), and on the flank of Kiluaea in Hawaii Volcanoes National Park on the Big Island (the other two pictures). It is awe-inspiring to observe the descendants of a few very unlucky Canada Geese (or lucky?) who made a wrong turn 500,000 years ago and survived a terrifying journey over a very large ocean. I'm glad we're trying to help them survive, instead of driving them to extinction.

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:

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