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Creature Feature: The Hawaiian Petrel ('Ua'u ) Has a Problem with Artificial Light


National Park Service ecologist Darcy Hu releases a Hawaiian petrel at Hawaii Volcanoes National Park. The rescued bird, which had probably become disoriented by artificial light, was exhausted when found near Volcano House. NPS photo.

The Hawaiian petrel (Pterodroma sandwichensis) -- Native Hawaiian name ‘ua‘u -- is a pelagic seabird that spends most of its life in the open ocean, but nests on the main Hawaiian islands, including several national parks. Because its numbers plunged to alarmingly low levels in historic times (it was once considered possibly extinct), the Hawaiian petrel has been federally protected since 1967. This endangered species still continues to face many hazards and needs our help.

Native Hawaiians dubbed this bird ‘ua‘u because of its distinctive nocturnal "oo-ah-oo" call during the breeding season. In addition to this moaning sound, the birds also produce calls that sound like the yaps, barks, and squeals of a small dog.

Pterodroma sandwichensis is fairly large, sturdy, and distinctive-looking, though not what you'd call handsome. An adult bird typically measures 16-17 inches in length and has a wing span of about three feet. Its head, tail and long, narrow wings are grayish-black, while its throat, forehead, cheeks and belly are white, its legs and webbed feet are bi-colored black and pink (mostly pink), and its hooked-at-the-tip bill is grayish-black.

The Hawaiian petrel is sometimes mistaken for a similar-looking bird, the wedge-tailed shearwater (Native Hawaiian name 'ua'u kani), which is about the same size and often found in the same general areas. The Galapogos dark-rumped petrel, which is nearly identical in appearance, is now considered a separate species.

The Hawaiian petrel is a truly pelagic species that spends most of its time in the open waters of the central North Pacific Ocean. During the breeding season, some individuals are known to forage as far north as the Aleutian Islands to find food for their nestlings, making great looping trips spanning several weeks and covering over 6,000 miles.

Petrels commonly flock with birds of other species over schooling tuna and other predatory fish. The petrel's steeply-banked, arcing flights and dives are a trademark feature. Squid supplies 50-75% of the Hawaiian petrel's diet, but the bird also eats fish (especially goatfish and lantern fish) and crustaceans.

Vast ocean waters, highly mobile behavior, inaccessible nesting areas, and other factors make it very difficult to know how many Hawaiian petrels there really are. Pelagic surveys, nest counts, and other evidence suggests that the total population is around 19,000, but it could very well be as low as 10,600 or as high as 34,400. The number of breeding pairs is a vital statistic, of course, and it appears that there are 6,500 to 8,300.

Petrels nest in burrows, primarily in remote mountainous and forested areas. The three to six- foot long burrows, each containing one white egg, are typically situated in crevices along large rock outcrops, in cavities under cinder debris or at the base of trees, or dug into in soil beneath dense vegetation such as ferns or bracken.

The birds begin breeding at about six years of age, forming long-lasting pair-bonds and returning to the same nest site year after year. Both parents incubate the single egg and then brood and feed their chick. Like many other seabirds, adults regurgitate food for their chicks.

Viewed from the land perspective, the birds display distinctly nocturnal behavior. Feeding at sea during the day, they return to their nesting burrows after nightfall. Unless caring for an egg or brooding, they depart on foraging flights before dawn.

The breeding season generally extends from March to October, with eggs laid in May and June. Fledglings usually leave the nest and fly to ocean feeding grounds sometime between mid-September and mid-December.

Haleakala National Park on Maui is a very important nesting site, with an estimated 1,200 to 1,800 burrows on the slopes of Haleakala Crater (some not used every year). There are also a few hundred nesting birds (at most) in two small colonies in the West Maui Mountains. All told, Maui's Hawaiian petrel population may total around 3,000 to 5,000 individuals at the peak of the breeding season. This represents a substantial increase over the past 20 years.

The island of Kaua`i has some good nesting habitat (especially the wet forests of Waimea Canyon) and is thought to host about 1,600 nesting pairs. On Lâna`i, as many as several thousand birds may nest in the cloud forest on the north side of the island.

Other locations have fewer numbers, but represent significant dispersion of nesting efforts. There are at least a few birds in remote areas of Moloka`i. On the Big Island (Hawai`i), a few pairs breed in the sparsely-vegetated summit areas of Mauna Loa and Mauna Kea, generally above 8,000 feet. (The birds are considered rare in Hawaii Volcanoes National Park.) Scattered small populations exist on some sea stack islets.

The Hawaiian petrel is federally protected, not only under the Migratory Bird Treaty Act (which protects all seabirds), but also under the Endangered Species Act. The latter protection was approved in 1967 because the bird's population was alarmingly low and declining at a rate that portended possible biological extinction. The bird thus became one of the first species to be ESA-protected.

Hawaiian petrels are under a lot of pressure in the modern world. The main hazards are predation, the loss and degradation of nesting habitat, ocean pollution, and the loss of nestlings making their first nocturnal flight to the sea.

Predation by mammals, especially rats, feral cats, mongooses and dogs, takes a heavy toll. The petrel has not developed natural defenses against these introduced predators, so it is highly vulnerable. Predators commonly feed on helpless chicks in their burrows.

Humans once accounted for much of the predation. In historic times, Native Hawaiians regarded the petrel as a delicacy. They harvested them by the thousands from nest burrows, by netting, and with the use of fires lit along nocturnal flight paths to disorient and exhaust the birds so they'd fall to the ground


Habitat loss and degradation is a huge problem. Urbanization, agricultural land-use, and related development in the main Hawaiian islands have made heavy inroads on nesting sites. The sites on Mauna Loa and West Maui are considered especially endangered.

Unfortunately, even nesting burrows in remote locations are vulnerable to trampling. The primary culprits are feral pigs and ungulates (mostly goats and mouflon sheep).

The impact of ocean pollution has not been fully assessed, but is considered significant. Among the known hazards are oil fouling, fisheries bycatch, and the biological amplification of pesticide residues in the oceanic food chain.

In the long run, the most serious oceanic hazard may prove to be disruptions in food availability brought about by global warming. Since the petrels follow tuna, any changes in tuna feeding patterns brought about factors such as shifts in currents or water temperatures will impact petrel food sources.

The proliferation of artificial lighting in Hawaii has yielded one of the very worst problems for the birds, a deadly phenomenon called "fallout." When petrels make their nocturnal flights to and from the sea, they use moonlight for guidance. Because they are exquisitely sensitive to light, they are easily confused by "stray light" such as street lights in urbanized areas or the lighting in coastal resorts. Many birds, especially fledglings making their first flight to the sea, collide with buildings, towers, power lines, guy wires, fences and other structures. Still more disoriented birds become exhausted and fall to the ground where they are run over by cars, killed by predators, or die of starvation and dehydration.

The Hawaiian petrel's problems are being addressed across a broad front with a combination of strategies and tactics designed to provide both direct and indirect benefits. Scientific research employing auditory surveying, banding, and sophisticated tracking and monitoring technology (such as using radar sampling, satellite telemetry, and passive integrated transponder tags) is adding valuable new information about nesting sites, at-sea habitat (foraging routes, feeding areas) and various poorly-understood aspects of petrel behavior. Habitat restoration and protection efforts, such as the construction of perimeter fencing (exclosures), have rescued some nesting sites that might otherwise have been lost. Some efforts has been directed toward reestablishing nesting at some abandoned breeding sites. Predator control programs using traps, rodenticides, and other pest control methods have removed many rats, feral cats, mongooses, and other predators. Even the switch to digital television benefited the birds through the removal of analog transmission towers that were collision hazards.

Interagency cooperation plays a vital role. At Haleakala National Park on Maui, for example, the U.S. Fish and Wildlife Service, the Hawai‘i Division of Forestry and Wildlife, and the National Park Service have partnered to control predators and protect nesting habitat.

The most heavily publicized effort on behalf of the petrels is an integrated program designed to minimize fallout losses by eliminating stray light and rescuing grounded birds. Reducing stray light means a lot of things, including:

• Turning off unnecessary outdoor lights.
• Replacing fixtures that scatter light in all directions with directional fixtures that point down and away from the beach.
• Shielding light sources to direct the light only where it is needed.
• Replacing high-intensity lighting with 40-watt yellow "bug lights".
• Using drapes on windows to prevent leakage of interior lights.

The systematic reduction of stray light can play a very important role. On Kaua`i, for example, the power company darkens, turns off, or shields all 3,000 of the island's street lights between mid-September and mid-December.

Rescuing grounded birds -- a tactic that admittedly addresses the symptoms of fallout, not the causes -- means educating the public and facilitating rescue and rehabilitation efforts. NGOs and government agencies have played an important role in publicizing the programs, which have saved thousands of grounded birds. Biologists from Haleakalā National Park and the State Department of Land and Natural Resources perform essential services, including assessing grounded birds for injuries and safely releasing birds back into the wild.

Anyone finding a grounded seabird on land (leave them alone on the water) is asked to protect it from hazards (such as cars, dogs and cats), place it in a covered, well-ventilated cardboard box, keep it in a cool or shaded place, refrain from giving it food or water, and report the find by calling Haleakala National Park Dispatch at 877-428-6911.

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