Volcano Watch: Seabirds struggle for survival on Mauna Loa

The endangered ‘ua‘u (Hawaiian petrel) is an endemic seabird that nests in deep lava rock burrows on the rugged high-altitude slopes of Mauna Loa. Despite the remote location, ‘ua‘u are not safe from cats. In order to protect this vulnerable species, the National Park Service (NPS) teamed up with the National Fish and Wildlife Foundation, U.S. Fish and Wildlife Service, American Bird Conservatory, Hawai‘i Pacific Parks Association, and the Pacific Cooperative Studies Unit at the University of Hawai‘i to build a five-mile long cat-proof fence in Hawai‘i Volcanoes National Park. The specifically designed barrier is more than six feet high, and has a curved top section that prevents cats from climbing over it.

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

A young ‘ua‘u exercises its wings in preparation for its first flight directly out to sea. The ‘ua‘u, or Hawaiian petrel, is a federally endangered native seabird that nests at high elevations on Mauna Loa volcano. For more information, please visit the Hawaiʻi Volcanoes National Park website: https://www.nps.gov/havo/learn/nature/uau.htm. NPS photo.

A young ‘ua‘u exercises its wings in preparation for its first flight directly out to sea. The ‘ua‘u, or Hawaiian petrel, is a federally endangered native seabird that nests at high elevations on Mauna Loa volcano. For more information, please visit the Hawaiʻi Volcanoes National Park website: www.nps.gov/havo/learn/nature/…. NPS photo.

High on the slopes of Mauna Loa, the largest active volcano on Earth, a unique Hawaiian seabird struggles for survival. The ‘ua‘u, or Hawaiian petrel (Pterodroma sandwichensis), spends most of its life at sea, returning to Mauna Loa only to nest and rear young in high-elevation, underground burrows.

It is estimated that historic ‘ua‘u populations were likely in the hundreds of thousands to millions of birds, with nests ranging from sea level to high mountain slopes throughout the main Hawaiian Islands. Today, the ‘ua‘u still occurs on several islands, but has become one of the most endangered seabirds in Hawaii.

Many threats have contributed to the decline of this endemic species, including historic hunting by humans, non-native predators, and habitat loss. More recently, inflight collisions with structures and groundings caused by disorienting artificial lights have taken a toll on the species.

On the Island of Hawaiʻi, ‘ua‘u once nested from the lowlands to the upper slopes of the volcanoes. They are now limited to high elevation sites on Mauna Loa and, possibly, steep cliffs on Kohala. Biologists have monitored remote nesting colonies on Mauna Loa for over two decades, and now estimate the population to be only 75 breeding pairs.

The somewhat mysterious life history of ‘ua‘u makes monitoring this species extremely challenging. ‘Ua‘u are pelagic, spending much of their lives at sea, coming to land only for nesting. They forage in distant feeding areas—in some cases, as far north as the Aleutian Islands—and fly to and from nesting areas at night.

On Mauna Loa, ‘ua‘u nest in remote underground burrows that are so deep they can’t be seen. Biologists are incorporating new technologies, including remote cameras and satellite transmitters, to better understand the species.

῾Ua῾u belong to the taxonomic order Procelleriformes, as do albatrosses, shearwaters, and other petrel species. Like their relatives, ‘ua‘u are long-lived (30-plus years) and do not breed until 4–6 years of age. Once nesting begins, both parents take turns incubating a single egg for roughly two months.

After an ‘ua‘u egg hatches, the adults head out to sea to feed on squid and fish, with foraging trips lasting from several days to several weeks at a time. The chick stays in its burrow, often alone, and waits for its parents to return with food.

After about three months, the growing ‘ua‘u chick ventures out of the burrow to exercise its newly feathered wings. Within weeks, it fledges, or takes its first flight, directly out to sea.

‘Ua‘u face many dangers during their time on land. Because they have no natural defenses, both adults and chicks are easy prey for introduced animals like feral cats and mongooses.

‘Ua‘u are also at risk when flying between nest sites and the sea. Birds have collided with unexpected structures along flyways, such as wind turbines and power lines. Artificial lights casting an upward glow can disorient ‘ua‘u, causing them to land in unsafe areas, where they are susceptible to predators and cars, and where they may not be able to launch back into flight.

The impacts of additional threats to ‘ua‘u, such as climate change and marine plastics, are not yet fully understood.

Fortunately, government agencies, private organizations, utility companies, and landowners have joined forces to reduce threats to ‘ua‘u and other Hawaiian seabirds. Hawai‘i Volcanoes National Park, with the help of several partners, recently completed a barrier fence to exclude cats from a key nesting area on Mauna Loa (youtu.be/m1MfyDbteVw). Collaborative conservation efforts, like this fence, are critical for the protection of ‘ua‘u and other sensitive species.

November is fledging season for ‘ua‘u on Mauna Loa. Island residents can play a role in helping these young birds reach the sea: Direct outdoor lights downward and shield the tops of lights to minimize disorientation of the birds as they fly between the mountain and the sea. Keep domestic cats inside or in outdoor enclosures, and avoid contributing to feral cat populations by preventing unwanted litters of kittens.

To report a grounded seabird in Hawai‘i Volcanoes National Park, call park dispatch at (808) 985-6170. Outside the park, contact the Department of Land and Natural Resources Division of Forestry and Wildlife at (808) 974-4221.

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