Status and management of the Palila, an endangered Hawaiian honeycreeper, 1987-1996

Abstract

A single, relictual population of Palila Loxioides bailleui, a Hawaiian honeycreeper, survives on the slopes of Mauna Kea volcano on the island of Hawai'i, where it feeds principally on flowers and green seeds of the mamane tree Sophora chrysophylla. The Palila was listed as an endangered species by state and federal governments because of continuing damage to its habitat by browsing Feral and Mouflon Sheep Ovis aries and O. musimon and Goats Capra hircus and because of the bird's restricted range and low numbers. Ecology of the Palila was studied from 1987 to 1996. Annual population estimates fluctuated between 1 600 and 5 700 and averaged 3 400 birds. Estimates varied with availability of mamane seeds, which are less abundant in drought years. In drought years, most birds did not attempt to breed, and survival rates were lower because of a shortage of food. Availability of mamane seeds also showed large seasonal variability. While some nests were preyed upon by Owls Asio flammeus, Cats Felis catus and Rats Rattus rattus, losses were high at the end of the season from unexplained death of eggs and chicks. Genetic studies did not implicate inbreeding depression. Neither avian malaria nor avian pox appeared at this site, where the mosquito vector was absent. However, weather and food shortage worsened towards the end of the nesting season. Availability of food and habitat remain the principal factors limiting increase in the Palila population. Recovery efforts now focus on reducing numbers of feral ungulates, fire management, removing mammalian predators, and developing techniques for captive propagation and introduction to currently unoccupied sites within the bird's former range. Reforestation adjacent to the Mauna Kea Forest Reserve would allow the Palila population to expand and grow.

Response of palila and other subalpine Hawaiian forest bird species to prolonged drought and habitat degradation by feral ungulates

“…The population declined each year thereafter, when drought conditions were interrupted on only six occasions, each lasting from 1 to 7 months. Dry conditions were strongly associated with lower mā mane pod production, and because palila survival and reproduction are reduced when pods are scarce (Lindsey et al, , 1995Pratt et al, 1997), fewer palila likely nested during the drought. Nevertheless, the relationship between nesting attempts and pod availability is weak , suggesting that age structure, sex ratio, or other factors also might influence annual nesting activity.…”

“…Data on weather conditions and on the ecology of palila, mā mane, and naio were not collected continuously throughout the 14-year study period, but information overlapped sufficiently to allow us to explore major relationships. Additionally, earlier studies provide a basis for understanding how drought affects the breeding and survival of passerines (Banko et al, 2002a;Lindsey et al, 1997;Pratt et al, 1997) and the phenology and productivity of mā mane and naio (Banko et al, 2002b). Although palila are the only birds that feed on mā mane seeds, a number of other passerines forage in mā -mane for nectar and arthropods, including the ubiquitous, native Hawaii 0 amakihi (Hemignathus virens virens) and the widespread, introduced Japanese white-eye (Zosterops japonicus), both generalist foragers.…”

Differential parasitism of seed-feeding Cydia (Lepidoptera: Tortricidae) by native and alien wasp species relative to elevation in subalpine Sophora (Fabaceae) forests on Mauna Kea, Hawaii

“…Sophora trees represent over 98% of the forest canopy from 2300 to 2800 m elevation (Hess et al 1999), and provide nesting and foraging habitat for several endemic bird species (Scott et al 1986;Hess et al 2001). The seeds of Sophora are the primary food resource of palila, Loxioides bailleui Oustalet (Fringillidae: Drepanidinae), an endangered forest bird endemic to Mauna Kea (Van Riper 1980;Pratt et al 1997;Banko et al 2002). Sophora seeds are also the only known host for several species of endemic Hawaiian Cydia (Lepidoptera: Tortricidae) caterpillars (Zimmerman 1978).…”

Availability of food resources, distribution of invasive species, and conservation of a Hawaiian bird along a gradient of elevation

“…Introduced browsers constitute the most important threat to Sophora (Scowcroft & Giffin, 1983), and nearly 47,000 feral sheep ( Ovis aries L.) were removed from Mauna Kea during the 1930s and 1940s to protect the forest and watershed (Bryan, 1947). Although ungulate threats have not been eliminated (Juvik & Juvik, 1984), they have been reduced sufficiently to allow us to identify other threats (Pratt et al ., 1997). Possibly because Sophora seeds contain high levels of secondary compounds (Banko et al ., 2002) they seem not to be preferred foods of introduced rodents (Amarasekare, 1994).…”