An endangered palila pauses at the open hatch of its release aviary, taking one last glance at its surroundings before taking its flight to freedom (see image at right). This palila is one of seven that were airlifted by helicopter in early March 2009, up to a site known as Puu Mali, on the northern slopes of Mauna Kea, Hawaii’s tallest volcano. All seven palila were hatched in previous breeding seasons at the Keauhou Bird Conservation Center (KBCC) as part of the Hawaii Endangered Bird Conservation Program’s ongoing effort to restore the palila population and thereby help to prevent the species’ extinction.
Up at Puu Mali, the program’s field crew eagerly anticipated the birds’ arrival and had prepared two release aviaries. For just over two weeks, the palila remained inside these release aviaries while orientating themselves to the mountainside that was soon to become their home. Up at an altitude of 8,000 feet (2,400 meters), Puu Mali experiences surprisingly bitter, cold nights, so this was also an opportunity for the palila to acclimate themselves to the novel temperatures while being fueled by the unlimited food provided by the field crew.
The palila Loxioides bailleui is endemic to the Big Island of Hawaii. It is restricted to the dry, subalpine scrubland of Mauna Kea, which supports forests of mamane trees. The mamane is a Hawaiian endemic tree belonging to the pea family that produces seedpods that are a vital food source for the palila. Not only do the palila primarily eat the “beans” of the mamane, but the moth caterpillars lurking inside the pods are thought to supply a valuable source of protein, particular for palila nestlings.
But the mamane forests, and therefore the palila, are under threat from feral cattle, sheep, and goats. These ungulates browse on the mamane saplings, preventing the new generation of mamane trees from establishing, and also strip bark and kill mature trees. The palila’s habitat has become so fragmented that the birds lack “corridors” that would enable them to migrate seasonally around the mountainside, following the fruiting of seedpods at different elevations. Additionally, feral cats and black rats have a major impact on nesting success as nest predators; it is thought that feral cats may even be causing a shift in population demographics, by depredating mature females incubating on the nest. Fortunately for the palila, the majority of its remnant habitat lies above the “mosquito line,” now estimated to be at an elevation of 5,000 feet, so avian malaria has impacted palila less than the many other critically endangered (and recently extinct) species of Hawaiian forest bird.
The majority of the palila population is found on the southwestern slopes of Mauna Kea, but we have been undertaking experimental releases of palila at Puu Mali, within the historic range of the species. In tandem with the releases, a team from the U.S. Geological Survey Biological Resources Division has translocated several cohorts of palila from the southwestern slopes of Mauna Kea. Preliminary evidence suggests that Puu Mali is able to support a population of palila long-term, despite only limited protection of the habitat from exotic predators and ungulates. Furthermore, released captive-bred birds appear to act as a “magnet” for the translocated flock that otherwise appears to have a strong fidelity to the southwestern slopes.
On Wednesday, March 18, 2009, the hatches of the release aviaries were opened for the fourth time since 2003. Within an hour, all seven birds were busy foraging in the canopy of mamane trees. As hoped, this spring appears to have provided a plentiful crop of mamane seedpods and flowers, with the result that the released birds have shown very little interest in returning to the open aviaries where supplemental food continues to be provided. In fact, this has enabled the released birds to forage far and wide, up to six miles (10 kilometers) away from the release site. This is presenting quite a challenge for the field crew who continue to monitor the success and survival of the birds by the use of radiotelemetry: long hikes up the cinder scarp and bumpy drives around the mountainside are a daily activity.
At the moment, the field team reports that five birds are being observed daily, alive and well, while a sixth bird has been proving more elusive to monitor. Unfortunately, the seventh bird was found dead a few days after release, apparently the victim of an introduced predator…a sad reflection of the ongoing threats to the palila population.
Meanwhile, news has just reached the field team that the palila flock at the KBCC has just started nest building. We now intend to intensify our release effort, with the goal of establishing a viable population at Puu Mali, so the program’s biologists eagerly await this season’s hatching of chicks, future recruits for release into the mamane forests on the slopes of Mauna Kea.
Richard Switzer is a conservation program manager for the San Diego Zoo’s Institute for Conservation Research.
Read a previous blog about palila.
Read more blogs from Hawaii Endangered Bird Conservation Program staff.