By Jan TenBruggencate
An expanding forest of introduced pines on Haleakalā could present another threat to the survival of the ‘ua‘u or Hawaiian petrel, a charismatic open-ocean seabird that once nested from sea level to the highest Island peaks.
Ground nesting birds in the Islands are at risk from many causes, and non-native animals like cats, rats, pigs, goats, axis deer, mongooses and even stray dogs are the most serious. But on Haleakalā, pine trees are expanding into new areas of native forest and altering habitat. The danger to the birds is that a dense pine canopy increases the threat of fire and eliminates the uluhe and ‘ama`u fern cover that helps protect the ‘ua‘u from direct access by cats and other predators.
Seagoing Hawaiian petrels, cousins to the shearwaters, are believed to have once been the most populous seabird in the Islands. They were an abundant source of food for native Hawaiians, and their burrows were vulnerable to foot traffic, agricultural development and predators.
By the time Westerners arrived in the Islands, the petrels were gone from O‘ahu, and their nesting areas had withdrawn to remote mountain locations on other islands. But the predators followed them even there. Today, one of the largest surviving nesting populations is high on Haleakalā.
At Home in Waikamoi
Here, in The Nature Conservancy’s 9,000-acre Waikamoi Preserve, researchers are trying to establish what’s happening to the Hawaiian petrel, one of the preserve’s several endangered species.
“There certainly are a lot of petrels in the Waikamoi area. I’ve looked at them with night vision goggles, and it looked like the old video game Space Invaders—so many birds,” said Pat Bily, a Nature Conservancy Maui biologist.
There is no reliable estimate of the Waikamoi area population, or specifically where they are.
“We are in the middle of learning,” said Jay Penniman of the Maui Nui Seabird Recovery Project. One of his key tools is the automatic acoustic monitor or song meter. These recording devices have been delivered by helicopter to remote, high-elevation locations, 4,000 to 7,000 feet up, on East Maui, including Waikamoi, the Ko‘olau Forest Reserve and the Hanawī Natural Area Reserve.
“With the song meters, we can collect sound at night when the birds are flying in. They call in the evening when they return to the colonies from feeding at sea,” Penniman said.
Both Penniman and Bily feel the largest surviving populations may be on the steepest slopes. Penniman’s six-member staff is searching the cliffs, where they may be better protected from predators.
“We plan to rappel down the ʻĀinahou pali to see if they are nesting there. We hope to determine whether we can further protect those colonies, perhaps with trapping, baits or moving birds into a predator proof enclosure,” Penniman said.
At Waikamoi, The Nature Conservancy’s management focus is the larger ecosystem. For seabirds, it partners with groups like Penniman’s Maui Nui Seabird Recovery Project, an agency of the University of Hawai`i’s Pacific Cooperative Studies Unit.
The good news is that management can have positive impacts. In neighboring Haleakalā National Park, where the ‘ua‘u also nests, field experts like Cathleen Bailey, a supervisory wildlife biologist, have been working at it for decades.
“For the last 30 years, we have been doing predator control, and we have seen a 10-fold increase in Hawaiian petrel populations since 1960,” she said.
And now the pines. A great mass of pine seed was released in the 2007 pine forest fire at Polipoli on the slopes of Haleakalā, and the spread of a soil fungus that helps pines grow has let them thrive in areas where they normally would not.
Teams are responding with various trials to find the best control methods in the rugged, inaccessible terrain.
“Predation by feral animals remains the greatest threat to the petrels,” Bily said. “But the pines are altering the native ecosystem, and that’s not good for the native species that depend on it.”