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March 16, 2000

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Island Castaways

The home of over 5 million breeding seabirds, Laysan Island is an uninhabited Hawaiian atoll formed from coral deposits atop a 20 million-year-old submerged volcano. Today the highest point of what was once "Laysan Mountain" is only about 12 meters (40 feet) above sea level, and a person can walk the perimeter in about 3 hours. The interior of the island holds a large, salty lake 2-4 times the salinity of the ocean and full of bright pink brine shrimp. Mudflats surround the lake and in the springtime are covered with clouds of small flies. The interior of the island is vegetated with native bunch grasses.

By day, the small, endangered Laysan Duck hides in the thick grass and is invisible to both the soaring seabirds overhead and the researchers who study them. The glossy brown ducks with spectacle-like white eye-rings emerge from their hiding places before sunset and congregate at the lake or coastal tidepools. Some begin feeding in the vegetation or on the shrimp and flies around the lake. They disappear into the bunch grasses again before dawn.

About 90 years ago there were no bunch grasses left on the island, after rabbits were introduced in the early 1900s and ate all the vegetation. This catastrophe brought the Laysan Duck to the brink of extinction. The species miraculously recovered from a population of less than 10 adults, when the rabbits were eliminated and the vegetation grew back. Unfortunately, three other landbirds, the Laysan Rail, Laysan Millerbird, and Laysan Apapane did not survive, due to the damage caused by the rabbits. Laysan has been designated as a National Wildlife Refuge since 1909, and the ducks were among the original endangered species listed in 1964 because of the threat of their extinction. Today there are fewer than 400 wild Laysan Ducks, found only on Laysan Island.

The Laysan Duck has the most restricted range of any duck species. Although they can fly, they don't leave the island, even when there is a drought, a big storm, or a disease epidemic. Perhaps Laysan is the safest place to be, because there are no mammalian predators there. Like many of Hawai`i's species, the Laysan Duck evolved without rats, cats, and mongooses and is ill-suited to a habitat invaded by non-native predators. The ducks are very curious and will approach humans for a closer look.

The effects of human-caused change have been most severe for island birds. Until 1995, the Laysan Duck was thought to have inhabited only the island for which it was named. However, paleontologists have recently discovered remains of Laysan Ducks from Lisianski, Kaua`i, O`ahu, Moloka`i, Maui, and Hawai`i.

Bones from adult and flightless juvenile Laysan Duck have been found at many diverse areas on Hawai`i Island, including higher elevations of Hualalai, Mauna Kea, and Mauna Loa. Remains were also found in lower elevations near the coast at South Point. It is likely that Laysan Ducks inhabited all the islands of the chain. Perhaps the ducks flew between the Hawaiian Islands until the risk of dispersing increased after the arrival of humans and other mammals; those flying between islands did not survive. Thus, the Laysan Duck has been restricted to Laysan Island only since the time period between 1840 and 1890!

Isolated populations are extremely vulnerable to extinction from chance events and human-caused disturbance. The population on nearby Lisianski Island vanished after successive shipwrecks on the island in the 1840s. The Laysan Duck has been missing from the main Hawaiian Islands for only about a thousand years. The fossil evidence has revealed that the Laysan Duck is essentially an island castaway. Perhaps it could be restored to other predator-free islands.

Eruption Update

Eruptive activity of Kilauea Volcano continued unabated during the past week, and a glow from Pu`u `O`o crater was visible at various times. Lava is erupting from Pu`u `O`o and flowing through a network of tubes toward the coast. Occasional breakouts from the tube system above and on the face of Pulama pali produce short-lived `a`a and pahoehoe lava flows. One flow is entering the ocean at Lae`apuki, and a second flow, located to the east of the first flow, is active in the area near Waha`ula. The public is reminded that the ocean-entry areas are extremely hazardous, with explosions accompanying unpredictable collapses of the new land. The active lava flows are hot and have places with very thin crust. The steam clouds are highly acidic and laced with glass particles.

There were two earthquakes reported felt during the week ending on March 16. Residents of Hilo felt an earthquake at 4:56 a.m. on March 10. The magnitude-3.3 temblor was located 12 km (7.2 miles) southeast of the summit of Kilauea Volcano at a depth of 7.9 km (4.7 miles). The second earthquake was reported felt by residents of Honaunau at 11:04 p.m. on March 13. The magnitude-2.4 earthquake was located 4 km (2.4 miles) south Of Honaunau at a depth of 13.6 km (8.1 miles).

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Updated: 20 Mar 2000