Long-Term Population Variability in the Palila, An Endangered Hawaiian Honeycreeper

Annual surveys of the entire range of the endangered Palila (Loxioides bailleui Oustalet) on Mauna Kea, Hawai'i, were conducted during 1980-1995. The majority of the Palila population was found on the southwestern slope of Mauna Kea near Pu'u La'au, and the range of Palila has not changed since 1975. The Palila population was highly variable. Mean population size during 1980-1995 was 3390 ± 333 SE, but the population ranged from 1584 ± 324 in 1985 to 5685 ± 535 in 1981. Population size outside the population center near Pu'u La'au has decreased significantly since 1980. MATERIALS AND METHODS Hawaiian forest birds and may prevent Palila from recolonizing portions of their former range below 1800 m elevation (Scott et al. 1984, van Riper et al. 1986). Degradation and fragmentation of the mamane woodland by introduced feral sheep (Ovis aries) and mouflon (Ovis musimon) led to two lawsuits in the 1980s to halt browsing of mamane (Scowcroft and Giffin 1983). Most of the feral ungulates have now been removed from Mauna Kea, and the forest is showing increased regeneration of mamane and other plant species. In this study, we present results of 16 annual surveys of the entire range of Palila. We sampled the same locations established by the Hawaiian Forest Bird Surveys (Scott et al. 1986) to document long-term changes in population size and range of Palila. The 250-km2 study area encompassed the entire mamane and mamane-naio woodland on Mauna Kea volcano on the island of Hawai'i. This subalpine forest extends from 1800 to 3000 m elevation and is dominated by short-stature (3-10 m) trees (Scowcroft and Giffin 1983, Scott et al. 1984). Mamane occurs around the entire mountain, but naio is mainly restricted to the southern and southwestern slopes. Rainfall averages 3575 em annually. 363 THE PAULA (Loxioides bailleui Oustalet) is an endangered Hawaiian honeycreeper (Fringillidae, Drepanidinae) currently found only in subalpine woodlands of Mauna Kea on the island of Hawai'i (Figure 1). The species is highly dependent upon the mamane (Sophora chrysophylla [Salisb.] Seem.) tree, from which it obtains the unripe seeds that are its primary food (van Riper et al. 1978, van Riper 1980a, Scott et al. 1984). Essentially all nesting occurs in mamane, even in areas where naio (Myoporum sandwicense A. Gray) is the dominant tree species. Scott et al. (1986) estimated that Palila now occupy <5% of the range they inhabited before the arrival of the Polynesians, and their current range may always have been marginal habitat (Scott et al. 1984). Habitat loss and modification, and annual variation in food supply in their high-elevation habitat are thought to be the primary reasons for the current small range and population size of the Palila. Avian malaria and avian pox have had devastating effects on 1Manuscript accepted 18 December 1995. 2National Biological Service, Pacific Islands Science Center, P.O. Box 44, Hawai'i National Park, Hawai'i 96718. 3Hawai'i Department of Land and Natural Resources, Division of Forestry and Wildlife, P.O. Box 4849, Hilo, Hawai'i 96720. 4National Biological Service, Idaho Cooperative Fish and Wildlife Research Unit, Moscow, Idaho 83843.