Science Center Objects

The palila is an endangered species of Hawaiian honeycreeper which exists only in subalpine forests dominated by māmane and naio on Mauna Kea Volcano. The diet of this finch-billed bird is unusually restricted; immature seeds, flowers, and insects found on māmane trees are critical to its existence. Māmane also is the preferred nesting substrate of the palila. Federal court orders have resulted in efforts to reduce populations of introduced feral sheep and mouflon sheep within Palila Critical Habitat, because they eliminate most māmane regeneration and modify forest structure. U.S. Fish and Wildlife Service specified mitigation of the effects of realigning Saddle Road (Highway 200) through Palila Critical Habitat to include restoration research to guide the conservation of palila within their core range and to develop techniques for reestablishing a population within a portion of former range. In addition, cattle grazing leases were withdrawn to allow forest restoration in areas formerly occupied by palila.

Palila eating mamane pods
A color-banded palila eats māmane seed pods. Photo: USGS

Overview:

The palila (Loxioides bailleui) is an endangered species of Hawaiian honeycreeper that exists only in subalpine forests dominated by māmane (Sophora chrysophylla) and naio (Myoporum sandwichense) on Mauna Kea Volcano. The diet of this finch-billed bird is unusually restricted; immature seeds, flowers, and insects found on māmane trees are critical to its existence. Māmane also is the preferred nesting substrate of the palila. Federal court orders have resulted in efforts to reduce populations of introduced feral sheep and mouflon sheep within Palila Critical Habitat, because they eliminate most māmane regeneration and modify forest structure. U.S. Fish and Wildlife Service specified mitigation of the effects of realigning Saddle Road (Highway 200) through Palila Critical Habitat to include restoration research to guide the conservation of palila within their core range and to develop techniques for reestablishing a population within a portion of former range. In addition, cattle grazing leases were withdrawn to allow forest restoration in areas formerly occupied by palila. The U.S. Army has also agreed to manage former palila habitat within Pōhakuloa Training Area for palila restoration. The concentration of palila in dry, highly flammable subalpine forest increases the threat of extinction due to many factors. Of greatest concern is the reduction of habitat carrying capacity resulting from long-term browsing by introduced sheep and the likelihood that drought severity and frequency is increasing due to climate change. Managers need both comprehensive ecological information for developing management strategies and practical information and techniques to effectively restore populations and habitats.

Radio tracking palila
Radio tracking palila on Mauna Kea Volcano. Photo: USGS

Project Objectives:

Processing a palila
Processing a palila. Photo: USGS

The Palila Restoration Project was initiated in 1996 by the U.S. Geological Survey to assist government agencies mitigate the effects of realigning Saddle Road (Highway 200) through Palila Critical Habitat (U.S. Fish and Wildlife Service 1998, Federal Highway Administration 1999). Ecological research on the palila, an endangered Hawaiian forest bird, carried out by the U.S. Geological Survey (formerly organized as the Research Division of U.S. Fish and Wildlife Service) since 1987 and research conducted by the Palila Restoration Project provided the scientific bases for developing a recovery strategy (U.S. Fish and Wildlife Service 2006) and its adaptive implementation.

The main objectives of the Palila Restoration Project were to develop techniques for reintroducing the palila to a portion of its former range, investigate the biological threats to the palila and its habitat, and synthesize the existing body of ecological knowledge concerning the palila to facilitate the recovery of the federally endangered palila.

Applying glue to the back of a palila to attach a transmitter
Applying special glue to attach a radio transmitter to the back of an adult palila. Photo: USGS

Five broad study themes formed the research framework:

  1. Population reintroduction and restoration
  2. Demography and breeding ecology
  3. Habitat use and food ecology
  4. Vegetation ecology
  5. Predator ecology and management

Highlights and Key Findings:

Our research demonstrated that the range of the palila has contracted to a small area on the western slope of Mauna Kea and that palila numbers have declined dramatically since 2003. Palila recovery is closely linked to improving habitat carrying capacity, which continues to be eroded by invasive sheep. Sheep browse māmane trees, which provide seeds that are critical to the survival of palila. Another factor affecting carrying capacity is drought, which reduces the production of māmane seeds. Drought has occurred frequently since 2000. About one-third of māmane trees are less than 20 years old, indicating that culling populations of invasive sheep promotes forest recovery. Increasing māmane cover across the landscape might increase the availability of the palila’s main food even when seed crops are reduced by drought.

4 chicks: 3 female technicians hold a palila nestling
"4 chicks!" Three research technicians hold a palila nestling. Photo: USGS 

The northern slope of Mauna Kea offers the best opportunity for reestablishing a second population of palila. We translocated 188 palila in six experimental trials during 1997–2006 from western to northern Mauna Kea. Based on radio-tracking and visual observations, 21% of 173 translocated birds returned to the western slope, but 34% remained longer than two months. There was no difference in the persistence of birds among trials, age classes, or sexes. The mortality of translocated birds was not significantly different from that of non-translocated birds. Reintroduced palila reproduced annually during 2004–2008, nesting on 23 occasions and producing 19 clutches of eggs and 13 fledglings. Nine fledglings survived to independence, and six survived into the next breeding season. One of these females later nested with a translocated male and together produced a fledgling (F2 generation), demonstrating that translocation could be a viable method for creating a self-sustaining population of palila. We also monitored the release of captive-reared palila and found that some males nested successfully with translocated or wild females.

Feral cats depredate 8-11% of wild palila nests annually. They also prey on reintroduced palila, and pose a significant threat to the reestablishment of populations. Although difficult to remove from palila habitat, we demonstrated methods of feasibly reducing their impacts.