Report on 16 years of research on palila now available online

A cooperative research unit of UH Hilo publishes years of studies on the palila, a critically endangered forest bird found only on Maunakea. With the publication, the palila becomes the most thoroughly documented Hawaiian bird species.

Palila on branch. Beautiful little bird with gold, gray and white coloring.
A palila (Loxioides bailleui) selects a seedpod from a māmane (Sophora chrysophylla) tree high on the western slope of Maunakea, Hawai‘i. The palila’s ecology and existence are inextricably linked to green māmane seeds, their critically important food. Chronic shortfalls in the supply of māmane seedpods could lead to the extinction of the palila. Photo by Jack Jeffrey,
Paul Banko
Paul Banko

A comprehensive report covering 16 years of research on the palila, a critically endangered Hawaiian forest bird, has been made available by the Hawaiʻi Cooperative Studies Unit of the University of Hawaiʻi at Hilo as part of its technical reports series. The report is part of a cooperative research program between the Pacific Island Ecosystems Research Center of the U.S. Geological Survey and UH Hilo.

“Palila Restoration Research, 1996−2012” summarizes long-term studies on the conservation biology of the palila (Loxioides bailleui), and details how research results can be applied to the conservation of the bird and restoration of its habitat. The palila is found only on the upper slopes of Maunakea.

Edited by researcher Paul Banko, a USGS wildlife biologist and expert on the palila, and Chris Farmer of the American Bird Conservancy, with contributions from 23 other authors from UH Hilo and other partners, the new report highlights years of work of many hundreds of technicians and volunteers.

“Some results can be expected to have immediate, practical value, whereas other information is more likely to enlarge our understanding of the species so that conservation strategies can be adjusted as conditions change,” says Banko, co-editor of the new volume. Banko is a High High School alumnus who received his doctor of philosophy in wildlife science from the University of Washington, Seattle. He has been studying the palila for over 20 years.

The palila research was conducted in partnership with UH Hilo and supported by the Federal Highway Administration, U.S. Army Garrison-Hawaiʻi, the U.S. Geological Survey Wildlife Program, U.S. Fish and Wildlife Service, and the Hawaiʻi Division of Forestry and Wildlife.

With the publication of the report, the palila becomes the most thoroughly documented Hawaiian bird species. Topics covered in this extensive report include population dynamics and restoration research, demography and breeding ecology, predator ecology and management, and habitat use, food ecology, and vegetation ecology, and management implications.

The major goal of the population and restoration research was to develop methods for reintroducing palila to former range and for enhancing the main palila population on the western slope of Maunakea. Translocating palila proved successful in establishing a small breeding colony of palila on the northern slope of Maunakea that persisted for a number of years before disappearing during severe drought.

A key aspect of the research was documenting the roles of drought and habitat damage by feral sheep in the sharp decline in palila numbers after 2003. One of the outcomes of the decline was the disproportionate number of male palila in the population, suggesting that females suffered greater mortality under stressful conditions.

Introduced predators are a longstanding threat to Hawaiian birds, but before this research little was known about their ecology in upland Maunakea, their level of threat to palila, or methods for their control. Radio-telemetry was used to track feral cats, mongooses, and rats to determine home range characteristics and activity and movement patterns.

Diet studies revealed the roles of cats and mongooses as bird predators. Surveys revealed that populations of rats were relatively small compared to wet forest habitats and that large outbreaks of mice occasionally occurred. This new knowledge of small mammal ecology was applied to understanding the impacts of these invasive predators on palila and other forest birds and to refining control methods.

Due to the palila’s extreme dependence on the seeds and other resources provided by a single native tree, māmane (Sophora chrysophylla), its survival critically depends on the availability of that food and the quality of the māmane habitat. Native Cydia caterpillars, which also eat māmane seeds, were found to be another critical food source for palila, especially nestlings. These topics are discussed in chapters on palila home range characteristics, patterns of habitat use and foraging behavior, seasonal patterns of māmane flowering and seed set, and threats to māmane resources from invasive wasps, ants, and beetles.

The chapters in the section on vegetation ecology characterize the plant community in subalpine Maunakea to understand how palila recovery will be affected by existing and future habitat conditions and to identify areas where habitat restoration should be targeted. Palila Critical Habitat has been degraded for over a century by a variety of introduced ungulates, but especially sheep (both feral and European mouflon) and goats.

Since 1980, sheep and goat populations have been culled by public hunting and aerial shooting. This has led to widespread regeneration of māmane and other native plants, although vegetation recovery has been slow and uneven. Many species of weeds have also invaded subalpine Maunakea, further disturbing the native vegetation.

Field surveys and analysis of satellite imagery revealed the sparse distribution of māmane and other important native species around Maunakea, and the damage done by ungulates was quantified. The distribution of 15 of the most threatening invasive weeds was also mapped, and the consequences of fire for the subalpine vegetation were evaluated.

The full report, Hawai‘i Cooperative Studies Unit Technical Report HCSU-046, “Palila Restoration Research, 1996−2012,” by Banko, P. C., and C. Farmer, published by the University of Hawai‘i at Hilo, can be found online. An accompanying summary report is also available. This document and the research contained within represents the collaborative partnership between researchers from USGS and UH Hilo that has made these studies possible.

Adapted from USGS press release.