Carter T. Atkinson, Julie K. Lease, Nicholas P. Shema, Robert J.
Dusek, and Beth M. Drake.
USGS-Biological Resources Division,
Pacific Island Ecosystems Research Center,
P.O. Box 218,
Hawaii
National Park, HI 96718 |
Wet and mesic forests on the southwestern slopes of the island of
Hawaii are home to remnant populations of four species of endangered forest birds, including 'Alala (Corvus hawaiiensis), Akiapola'au (Hemignathus munroi), Hawaii Akepa (Loxops coccineus), and Hawaii Creeper (Oreomystis mana). While a number of things threaten these endemic species, high susceptibility to avian pox and malaria (Plasmodium relictum) is believed to be the primary factor preventing recovery of populations at elevations below 5,000 ft. We conducted a detailed study of the seasonal fluctuations, distribution, breeding sites, and infection rates of the primary vector of these diseases, Culex quinquefasciatus, along elevational transects through critical forest bird habitat. This information was used to test the effectiveness of source
reduction in reducing Culex populations. We found that primary oviposition sites were concentrated between elevations of 3,000 and 5,000 ft. in hollowed tree ferns that had been damaged by feral ungulates. Approximately 12,000 of these sites were
manually drained within an 800 hectare plot over a four month period. In spite of this effort, up to 30% of the oviposition sites were missed because of thick vegetation and difficult terrain. Reductions in adult Culex populations were not detected before and after treatment or when comparisons were made between treatment and control plots. While initial results were discouraging, source reduction is potentially feasible if it is
coupled with fencing and feral ungulate control and practiced over a wide enough area.
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