Hawaii's Endemic Birds
by
James D. Jacobi
National Biological Service
Carter T. Atkinson
National Biological Service
Hawaii's Endemic Birds | ||
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by James D. Jacobi National Biological Service Carter T. Atkinson National Biological Service |
| The endemic landbirds of Hawaii, particularly the Hawaiian honeycreepers, an endemic subfamily of the cardueline finches, are one of the world's most dramatic examples of adaptive radiation and speciation (see glossary) in island ecosystems (Freed et al. 1987; Scott et al. 1988). From what is believed to have been a single successful colonization of the Hawaiian Archipelago by an ancestral species from North America, the honeycreepers evolved into a diverse array of species and subspecies of birds with bills ranging from thick, seed-eating beaks of the palila (Loxioides bailleui), to small insectivorous bills as seen on the `amakihi (Hemignathus virens), woodpecker-like adaptations of the `akiapola`au (H. munroi), and large, decurved nectar-feeding bills of the `i`iwi (Vestiaria coccinea). | ||
| In addition to the honeycreepers, the historically documented endemic Hawaiian avifauna included three seabirds, several waterfowl, two raptors, and perching birds that include a species of crow, and representatives of Old World flycatchers, honeyeaters, and thrushes. In all, at least 71 endemic species and subspecies of Hawaiian birds existed at the time of Captain Cook's arrival in the Hawaiian Islands in 1778. Now, however, 76% of the Hawaiian birds are either extinct or endangered, and several of the remaining unlisted species are showing significant population declines. | ||
| The arrival of humans to the Hawaiian Islands--starting with the Polynesians more than 1,500 years ago and continuing following European contact--drastically changed many natural ecosystems, leading not only to the extinction of many plant and animal species, but also to a significant reduction in both range and abundance for many other taxa. Originally, the Hawaiian birds were found in all habitat zones on each island, but today few native forest birds are found below 610-m (2,000-ft) elevation, and many of the wetland areas that once provided abundant habitat for waterbirds have been destroyed. | ||
| Of the historically documented 71 taxa of endemic Hawaiian birds, 23 are now extinct, and 30 of the remaining 48 species and subspecies are listed as endangered or threatened by the U.S. Fish and Wildlife Service (USFWS 1992), many with few or only single populations remaining (Fig. 1; Table 1; Table 2). Studies of recently discovered fossil bird bones have further identified nearly 40 additional species of Hawaiian birds never seen alive by the post-Cook naturalists; many of these became extinct after the Polynesians arrived (Olson and James 1982; H. James, Smithsonian Institution, personal communication). |
Fig. 1. Current status of endemic Hawaiian bird species known to exist at the time of Western contact (1778). |
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Reasons for the Decline |
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| Many factors have been suggested to explain the decline of Hawaiian bird species since human colonization (Ralph and van Riper 1985; Scott et al. 1988). The most important and plausible of these include habitat loss (Berger 1981; Kirch 1982; Olson and James 1982; Jacobi and Scott 1985), susceptibility to introduced avian diseases (Warner 1968; Ralph and van Riper 1985; van Riper et al. 1986), predation by introduced mammals (Atkinson 1977), and competition from introduced birds (Mountainspring and Scott 1985) and arthropods (Perkins 1903; Banko and Banko 1976). Although no one factor is believed to be the single cause for the loss or decline of the Hawaiian birds, many biologists believe that habitat loss and avian diseases have had the greatest effect on native birds. |
Table 1. Historically known endemic Hawaiian birds that are now extinct. | |
Habitat Loss |
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| Habitat loss from forest removal and development in the Hawaiian Islands started when large tracts of mostly lower elevation land were cleared for agriculture by the first Hawaiian colonists. After European and American settlers arrived, starting in the late 18th century, habitat loss increased dramatically as agriculture and ranching expanded. Today, less than 40% of the land surface of Hawaii is covered with native-dominated vegetation (Jacobi 1990; S. Gon, The Nature Conservancy of Hawaii, unpublished data). Some of the most significant loss of habitat has occurred below 610 m (2,000 ft) elevation, where less than 10% of the native vegetation remains. In addition to direct clearing, all remaining native plant communities are further degraded by disturbance and competition from introduced plants and animals. | Table 2. Status of extant species and subspecies of endemic Hawaiian birds. Data summarized from Scott et al. (1986), Harrison (1990), Ellis et al. (1992) Engilis and Pratt (1993), and J. Jacobi (unpublished data). | |||||||||||
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| The current ranges of most Hawaiian forest birds appear closely tied to the distribution of forests dominated by native tree species. It is unclear whether this association is due to feeding specialization on native plants, or if other factors, such as disease or predators, restrict native birds from disturbed habitats. The only real exception to this is the Oahu `amakihi (Hemignathus virens chloris), which recently appears to be colonizing habitats dominated by introduced plant species around Honolulu. | ||
Avian Disease |
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| The accidental introduction of Culex mosquitoes in the early 19th century, and the importation and widespread release of domestic fowl, gamebirds, and cage birds with their accompanying diseases, are believed responsible for the establishment of avian pox virus and malaria (Plasmodium relictum) in Hawaiian forest bird populations (Warner 1968; van Riper et al. 1986). The concurrent fragmentation of native forests probably hastened the spread of mosquitoes and exotic birds into forest habitats, exposing native birds to avian pox (Perkins 1893; Henshaw 1902) and malaria. | ||
| Warner (1968) first identified pox and malaria as major pathogens of native forest birds. Van Riper et al. (1986) demonstrated that the highest incidence of malaria occurs in wet midelevation forests (between 900 m [3,000 ft] and 1,500 m [5,000 ft]) where populations of Culex mosquitoes overlap with highly susceptible native birds. Current investigations support these observations. Surveys for other disease agents identified a number of potentially pathogenic parasites and bacteria, but none has been implicated as a significant cause of mortality (van Riper and van Riper 1985). | ||
Introduced Predators |
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| While introduced rats (Rattus spp.), cats (Felis catus), dogs (Canis familiaris), and mongooses (Herpestes auropunctatus) have seriously affected nesting waterbirds, less information exists on the significance of these predators in restricting the distribution and abundance of upland forest birds in Hawaii (Atkinson 1977; Griffin et al. 1989). Several projects have begun in Hawaii to develop adequate control strategies for introduced predators and to monitor the response of forest bird populations to the reduction or elimination of these predators. | ||
Competition and Food |
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| Competition for nesting and food resources by introduced birds and food resource limitation by introduced arthropods (e.g., ants or wasps) are the two most difficult of the limiting factors hypotheses to evaluate. Although a study by Mountainspring and Scott (1985) found a negative association between several native and introduced bird species pairs, much more work is needed to understand the significance of these relationships. Similarly, preliminary evidence suggests that arthropods such as the introduced yellowjacket wasps (Vespula spp.) and several species of ants may seriously deplete the resident arthropods that many native birds eat, particularly during nesting (P. Banko, NBS, personal communication). | ||
Current Status |
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| Table 2 summarizes the most recent information on the status of endemic Hawaiian bird species. The population size for many forest birds comes from the Hawaii Forest Bird Survey, 1976-81 (Scott et al. 1986). While most of these numbers are more than 15 years old, they represent a distribution and abundance baseline upon which subsequent surveys can be based. The trend information in Table 2 is based on population surveys conducted during the past 15 years. | ||
| Seabirds | ||
| Three seabird species are endemic to Hawaii: the endangered dark-rumped petrel (Pterodroma phaeopygia sandwichensis), the threatened Newell's shearwater (Puffinus newelii), and the Hawaiian noddy (Anous minutus melanogenys). The first two relatively rare species nest in upland forest or subalpine and alpine sites. As with all of the ground-dwelling or nesting birds, the dark-rumped petrel and Newell's shearwater are extremely susceptible to predation by cats, dogs, rats, and mongooses during their long nesting period. A successful predator-control program in nesting areas for the dark-rumped petrel in Haleakala National Park on Maui has resulted in a significant increase in petrel productivity. Recently discovered nesting areas for the dark-rumped petrel and Newell's shearwater on the island of Hawaii offer similar opportunities to use predator control to reestablish significant breeding colonies for these species in upland habitats. | ||
| Waterbirds | ||
| Historically, the Hawaiian avifauna includes six waterbird species, five of which are typically found in and around fresh-, brackish-, and saltwater impoundments and estuaries (Engilis and Pratt 1993). The sixth species, the nene or Hawaiian goose (Branta sandwichensis), though occasionally found around water, most typically occurs in upland sites. | ||
| Continued loss of habitat and predation are the two biggest threats to the remaining Hawaiian waterbirds. Although the Hawaiian coastal zone formerly contained many large wetland areas, few remain. For example, the resort area known as Waikiki Beach was an extensive wetland that was drained in the early 1900's. Because introduced predators are a major threat to waterbirds in Hawaii, predator control has become essential in all waterbird-management programs. | ||
| An intensive captive propagation and release program has kept the nene from extinction. This ground-nesting goose, however, is extremely vulnerable to predation by introduced mongooses, cats, dogs, and possibly rats and is not able to sustain wild populations in most areas (Stone et al. 1983). A recently established population on the island of Kauai appears to be thriving, probably mostly because of the absence of mongooses on this island. | ||
| Both duck species endemic to Hawaii are endangered. The Laysan duck (Anas laysanensis) is known only from Laysan Island, a small atoll about halfway up the northwest Hawaiian Island chain. Although population levels have been as high as 600 birds over the past 25 years, they dropped to fewer than 50 during 1993 (T. Work, NBS, personal communication). Species confined to such a small geographical area are extremely vulnerable to natural disasters (e.g., hurricane damage) or human-related impacts (e.g., introduction of disease or predators to the island). | ||
| References | |
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Atkinson, I.A.E. 1977. A reassessment of factors, particularly Rattus rattus L., that influenced the decline of endemic forest birds in the Hawaiian Islands. Pacific Science 31:109-133. Banko, W.E., and P.C. Banko. 1976. Role of food depletion by foreign organisms in historical decline of Hawaiian forest birds. Pages 29-34 in C.W. Smith, ed. Proceedings. First Conference in Natural Sciences, Hawaii Volcanoes National Park. Cooperative National Park Resources Studies Unit, Department of Botany, University of Hawaii, Honolulu. 243 pp. Berger, A.J. 1981. Hawaiian birdlife. 2nd ed. University Press of Hawaii, Honolulu. 274 pp. Ellis, S. C. Kuehler, R. Lacy, K. Hughes, and U.S. Seal. 1992. Hawaiian Forest Birds Conservation Assessment and Management Plan, Final Report. Proceedings of the Hawaiian Forest Birds Conservation Assessment and Management Plan Workshop, 7-12 December 1992, Hilo, Hawaii. Published by the Captive Breeding Specialist Group, IUCN-The World Conservation Union/Species Survival Commission. 142 pp. Engilis, A., Jr., and T. Pratt. 1993. Status and population trends of Hawaii's native waterbirds. Wilson Bull. 105:142-158. Freed, L.A., S. Conant, and R.C. Fleischer. 1987. Evolutionary ecology and radiation of Hawaiian passerine birds. Trends in Ecology and Evolution 2:196-203. Griffin, C.R., C.M. King, J.A. Savidge, F. Cruz, and J.B. Cruz. 1989. Effects of introduced predators on island birds: contemporary case histories from the Pacific. Pages 687-698 in H. Ouellet, ed. Proceedings of the XIX Ornithological Congress. Vol. 1. Harrison, C.S. 1990. Seabirds of Hawaii. Comstock Publishing Associates, Cornell University Press, Ithaca, NY. 249 pp. Henshaw, H.W. 1902. Birds of the Hawaiian possessions. T.G. Thrum, Publisher, Honolulu, HI. 146 pp. Jacobi, J.D. 1990. Distribution maps, ecological relationships, and status of native plant communities on the island of Hawaii. Ph.D. dissertation, University of Hawaii, Honolulu. 291 pp. Jacobi, J.D., and J.M. Scott. 1985. An assessment of the current status of upland habitats and associated endangered species on the island of Hawaii. Pages 3-22 in C.P. Stone and J.M. Scott, eds. Hawaii's terrestrial ecosystems, preservation and management. Cooperative National Park Resources Studies Unit, University of Hawaii, Honolulu. 584 pp. Kirch, P.V. 1982. The impact of the prehistoric Polynesians on the Hawaiian ecosystem. Pacific Science 36:1-14. |
Mountainspring, S., and J.M. Scott. 1985. Interspecific competition among Hawaiian forest birds. Ecological Monographs 55:219-239. Olson, S.L., and H.F. James. 1982. Fossil birds from the Hawaiian Islands: evidence for wholesale extinction by man before western contact. Science 217:633-635. Perkins, R.C.L. 1893. Notes on collecting in Kona, Hawaii. Ibis 1893:101-114. Perkins, R.C.L. 1903. Vertebrata (Aves). Pages 365-466 in D. Sharp, ed. Fauna Hawaiiensis. Vol. 1, Part 4. The University Press, Cambridge, England. Ralph, C.J., and C. van Riper III. 1985. Historical and current factors affecting Hawaiian native birds. Pages 7-42 in S.A. Temple, ed. Bird conservation 2. The International Council for Bird Preservation, United States Section. The University of Wisconsin Press, Madison, WI. Scott, J.M., C.B. Kepler, C. van Riper III, and S.I. Fefer. 1988. Conservation of Hawaii's vanishing avifauna. BioScience 38:238-253. Scott, J.M., S. Mountainspring, F.L. Ramsey, and C.B. Kepler. 1986. Forest bird communities of the Hawaiian Islands: their dynamics, ecology, and conservation. Studies in Avian Biology 9. 431 pp. Stone, C.P., R.L. Walker, J.M. Scott, and P.C. Banko. 1983. Hawaiian goose research and management--where do we go from here? 'Elepaio 44:11-15. USFWS. 1992. Endangered and threatened wildlife and plants. 50 Code of Federal Regulations 17.11 and 17.12. 38 pp. van Riper, C., III, and S.G. van Riper. 1985. A summary of known parasites and diseases recorded from the avifauna of the Hawaiian Islands. 1985. Pages 298-371 in C.P. Stone and J.M. Scott, eds. Hawaii's terrestrial ecosystems: preservation and management. Cooperative National Park Resources Studies Unit, University of Hawaii, Honolulu. 584 pp van Riper, C., III, S.G. van Riper, M.L. Goff, and M. Laird. 1986. The epizootiology and ecological significance of malaria in Hawaiian land birds. Ecological Monographs 56:327-344. Warner, R.E. 1968. The role of introduced diseases in the extinction of the endemic Hawaiian avifauna. Condor 70:101-120. |
