Composition and Phenology of the Dry Forest on Mauna Kea, Hawaii, as Related to the Annual Cycle of the Amakihi (Loxops virens) and Palila (Psittirostra bailleui)

van Riper, Charles III
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Island Ecosystems IRP, U.S. International Biological Program
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An intensive 19 month phonological was carried out on the southwestern slope of Mauna Kea, Hawaii, from March 1973 through October 1974. This study was part of a larger six year project on the breeding ecology of two native birds in the region, and is only a preliminary report. Study areas were established at approximately 6,500, 7,000, and 7,500 feet elevation; five 100 x 100 feet (30.5 m x 30.5 m) phenology plots were measured within each study area and all the trees were tagged and measured. Percentage of canopy cover, flowering, and fruit production were measured monthly; index values were established for each phenophase so that they could be expressed graphically as well as analyzed statistically. The forest on this slope of Mauna Kea is composed almost entirely of mamane (Sophora chrysophylla) and naio (Myoporum sandwicense). Each of the three elevations studied has a significantly different composition of tree species; the birds present at each elevation appear to reflect the composition of the forest. The Palila (Psittirostra bailleui) and Akiapolaau (Hemignathus wilsoni) seem to be confined to the higher elevations where mamane is dominant (7,400 to 8,400 feet). Tree height and circumference at breast height (CBH) increase with elevation, although not significantly. Tree density in phenology plots decreases with higher elevation. Decreased density and the location of seedlings only in open areas suggest that water may be a limiting factor. Reproduction of mamane is severely curtailed in areas of high sheep-grazing pressure, but shows good regeneration in enclosed areas. Phenological data from Mauna Kea are similar to those from Mauna Loa. There appears to be seasonality in flowering, fruiting, and leaf fall in both mamane and naio, but seasonality is more difficult to interpret in the latter. Phenophases start gradually and are protracted; flushing and flowering show an inverse relationship. Precipitation peaks coincide with flowering peaks and may trigger this phenophase. Heavy rain may cause a decrease in flowering and an almost total loss of the pod crop in mamane. Behavioral patterns of both the Amakihi (Loxops v. virens) and Palila seem to be influenced by phenological patterns on Mauna Kea. The extended bloom period of mamane correlates with the protracted nesting season of the Amakihi. Canopy cover is at its maximum density when nesting starts, and remains fairly dense throughout the breeding cycle of the Amakihi. Surplus Amakihi leave an area when mamane bloom ceases, leaving only a few permanent residents; naio blossom visitation increases at this time. Palila nest throughout the period of peak pod production. When mamane pods are present the Palila was found to utilize mamane flowers young leaves, and naio berries. Phenological aspects of mamane appear to be much more important to the birds on Mauna Kea than those of naio. It would appear that naio serves only as a supplemental food source; naio berries are taken by Palila, House Finch (Carpodacus mexicanus frontalis), and Turkey (Meleagris gallopavo) in dry periods.
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Amakihi, Palila, Loxioides bailleui, Hemignathus virens
van Riper C. 1975. Composition and phenology of the dry forest on Mauna Kea, Hawaii, as related to the annual cycle of the Amakihi (Loxops virens) and Palila (Psittirostra bailleui). Honolulu (HI): Island Ecosystems IRP, U.S. International Biological Program. International Biological Program Technical Report, 51. 37 pages.
37 pages
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