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Palila

The palila (Loxioides bailleui) is dependant upon māmane (Sophora chrysophylla) and māmane/naio (Myoporum sandwicense) forests. Its diet consists primarily of unhardened māmane seeds, flowers, buds, and leaves [1]. Naio berries are also significant food source, especially when māmane production is low. The palila's annual and seasonal population density is strongly related to māmane pod availability. Most nesting occurs in māmane trees; most roosting in naio trees. The highest palila population densities occur in māmane-dominated or mixed māmane-naio forests near 7,550 feet with greater crown cover, taller trees, and a higher proportion of native shrubs in the understory. As māmane trees at different elevations produce flowers and fruits at different times of year, a wide belt of māmane forest will more consistently provide seeds to palilas throughout the year.

Fossil remains indicate that the palila formerly occurred at sea level on O'ahu, but in historic times has only been recorded at higher elevations on Mauna Loa, Haulalai and Mauna Kea on the island of Hawaii. In the 1890s it was "extremely numerous" in the māmane belt between 4,000 and 6,000 feet in the Kona region [1]. By the 1940s it was considered endangered because of its extirpation from Mauna Loa, Haulalai, and the mid elevations of Mauna Kea, but it was still locally common between 7,800 and 8,350 feet on Mauna Kea's western and northeastern slopes. Approximately 96% of the current palila population, and nearly all the successful breeding, occurs on the southwestern slope. Small declining populations occur on the northern and eastern slopes. The species' total range in 1980 and 2001 consisted of 54 square miles which represent 26% of the māmane woodlands remaining on the mountain.

Avian disease, predation by cats and rats, fire, and ungulate grazing are the primary causes of the palila's decline. The species is highly susceptible to avian malaria and its retreat from lower elevation forests is thought to have been partially caused by mosquitoes [1]. Mosquitoes are not a threat to the current palila population because the latter's range is above the former's, but the palila's ability to expand into lower elevations and recover is limited by mosquitoes. Egg predation by black rats and predation of nestlings and adults by feral cats may be responsible for up to 40% of all palila mortality. Lack of nesting in naio-dominated forests may be attributable to high levels of black rat use. Fire is a significant threat to the small dry forest area currently occupied by palilas, especially where exotic grasses and understory vegetation have increased fine fuels.

The most significant recent threat has been grazing by feral sheep, cattle, goats and mouflon. Sheep, cattle, and goats became established on Mauna Kea in the 1820s, severely degrading māmane forests. At upper elevations, their browsing lowers the tree line; at lower elevations it reduces tree density. Lower tree limbs are browsed, reducing tree productivity and palila food. Feral sheep became established on Mauna Kea in the 1820s, reaching a population of about 40,000 animals by the early 1930s [1]. The removal of some 47,000 feral sheep and more than 2,200 other feral ungulates in the 1930s and 1940s probably saved the palila from extinction [2]. Most remaining sheep were removed in the 1980s and 1990s due to court ordered protection of the palila's critical habitat [1]. In approximately 2004, the Department of Defense mitigated its impact to approximately 160 acres of critical habitat by establishing $15 million conservation fund to remove the remaining sheep, fence and restore habitat, and establish a new population.

The small populations on the southern and eastern slopes have been declining since 1980, while the much larger population on the southwestern slope has been slowly increasing [1]. Population estimates have fluctuated considerably but have increased overall [1]. The population was estimated at 1,614 in 1975 [4] and exceeded 2,700 in each of the last six year for which data are available (1996-2001) [1].

[1] U.S. Fish and Wildife Service. 2003. Draft Revised Recovery Plans for Hawaiian Forest Birds. Portland, OR.
[2] Banko, P.C., L. Johnson, G.D. Lindsey, S.G. Fancy, T.K. Pratt, J. D. Jacobi, and W.E. Banko. 2002. Palila (Loxioides bailleui). In The Birds of North America, No. 679 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
[3] Banko, P.C. 1998. Scientific Bases for Mitigation Plan. Pacific Island Ecosystem Research Center. http://biology.usgs.gov/pierc/mitigate/
[4] USFWS. 2005. Threatened and Endangered Animals in the Hawaiian Island: Palila / Loxiodes bailleui. U.S. Fish and Wildlife Service website (www.fws.gov/pacific/pacificislands/wesa/palila.html) accessed February 14, 2005.

Banner photo © Phillip Colla