COOPERATIVE NATIONAL PARK RESOURCES STUDIES UNIT UNIVERSITY of HAWAII at MANOA Department of Botany Honolulu, Hawaii 96822 (808) 948-8218
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COOPERATIVE NATIONAL PARK RESOURCES STUDIES UNIT UNIVERSITY OF HAWAII AT MANOA Department of Botany Honolulu, Hawaii 96822 (808) 948-8218 Clifford W. Smith, Unit Director Associate Professor of Botany Technical Report 47 The Impact of Malaria on Birds in Hawaii Volcanoes National Park Charles van Riper 111, Sandra G. van Riper, 1 M. Lee GoffI2 and Marshall ~aird3 Department of Zoology and Cooperative Park Studies Unit University of California Davis, CA 95616 USA 1 Arvintage Ranch R.R. #I, Box 776C Woodland, CA 95695 USA '~e~artmentof Entomology Bishop Museum P.O. Box 19000-A Honolulu, HI 96819 USA '~esearch Unit on Vector Pathology Memorial University of Newfoundland St. John's, Newfoundland Canada A1C 5S7 November 1982 UNIVERSITY OF HAWAII AT MANOA NATIONAL PARK SERVICE Agreement No. CX 8000 7 009 Contribution Number CPSU/UH 022 /Final TABLE OF CONTENTS Page LISTOFTABLES ............................. iii LISTOFFIGURES ............................ iii INTRODUCTION .............................. 1 Study Areas ............................ 3 Laboratory Techniques ....................... 4 RESULTS ................................ 8 Field Results ........................... 8 Infection Rates ....................... 9 Vector Distributions ..................... 12 Experimental Results ....................... 14 Altitudinal Exposure Experiment ............... 14 Asexual Malaria Cycle .................... 14 Sexual Malaria Cycle ..................... 17 DISCUSSION ............................... 19 Susceptibility of Hawaiian Birds to Malaria ............ 22 Forces Presently Operative on Native Bird Populations ....... 25 Immunogenetic Mechanisms ................... 26 Nonirnmunogenetic Mechanisms ................. 27 Malaria Arrival Date ....................... 30 CONCLUSION ............................... 36 GENERAL SUMMARY OF RESULTS ....................... 37 MANAGEMENT RECOMMENDATIONS ....................... 40 ACKNOWLEDGEMENTS ............................ 46 LITERATURE CITED ............................ 48 LIST OF TABLES Table Page 1 Nuher of birds captured per 100 net hours from 1979-1980 onMaunaLoa,Hawaii ...................... 54 2 Malaria infection rates throughout the annual cycle in birds from Mauna Loa, Hawaii .................. 55 3 Malaria infection levels in birds at different times of the year from mesic and xeric forests on Mauna Loa, Hawaii ..... 56 4 Success rate of sexual cycle transmission with -P. -r. capistranoae in Culex quinqefasciatus and Aedes albopictus in Hawaii ........................... 5 Presumed extinction dates of native land birds from the main Hawaiian Islands (Berger 1981) ............... 58 LIST OF FIGURES Figure Page Location of study sites on the east flank of Mauna Loa Vol.cano, Hawaii ......................... Total birds captured duringthe study .............. Average yearly percentage of birds infected with malaria on Mauna Loa, Hawaii ...................... Yearly percentage of infected individuals infected and parasite levels of malaria in species of avian hosts from Mauna Loa, Hawaii ........................ Infection rates and percentage of populations infected with avian malaria along an elevational gradient on MaunaLoa,Hawaii ........................ Maximum elevations at which mosquitoes were found on Mama Loa throughout the yearly cycle .............. iii Figure Page Yearly abundance of Culex (adult) on Island of Hawaii ...... 66 Percentage of individuals of challenged avian hosts resisting and surviving malaria challenge ................. 6 7 Parasite levels of avian hosts from Mauna Loa, Hawaii, over the patent period ..................... 68 Numbers of trophozoites, gametocytes, and schizonts in challenged avian hosts from Mauna Loa, Hawaii .......... 6 9 Parasite levels in avian hosts from Mauna Loa, Hawaii, overthe24 hourdailycycle .................. 70 Daily activity levels of mosquitoes from Mauna Loa, Hawaii ... 7 1 Native bird, malaria parasite, and vector abundances on MaunaLoa,Hawaii ........................ 7 2 Introduced and native bird malaria parasite levels over the annual cycle on Mauna Loa, Hawaii .............. 7 3 Pre- and post-malaria movement patterns of native Hawaiian birdsonMaunaLoa,Hawaii ................... 7 4 INTRODUCTION The Hawaiian Islands are the most isolated land mass in the world, lyinq in the middle of the Pacific Ocean over 4,500 km from North Anierica and 5,000 km from Asia. Because of their sterile volcanic origin and great distances from the continents, colonization was infrequent, hut when it did occur, the organi srns, isolated from mainldnd influences and cons faints, underwent rapid and extensi ve adaptive radiation. Among the most spectacular examples are the land birds, in which 10 of the 11 fami ies have endemic species. Unfortunately, more of these endemic spec es have become extinct than in any other comparable region of the world. There have been many proposed hypotheses as to why so many native bird species succumbed in the short time period following disc0ver.y of the Islands by Captain Cook in 1778; these include habitat destruction b.y man I and introduced ungulates, indiscriminate col lectinq of birds, competition with introduced hi rds, introduced predators, and introduced diseases. In this paper we will attempt to ascertain the role that the introduced vlalaria parasite has pla.yed in the decline of Hawaiian avifauna. Much concern has been expressed over the relationship between introduced di seases and the depletion of the native Hawai ian hi rds, hut the many papers addressinq this problem have been little more than technical criticisms and have not re-examined the under1,ying hypothesi s. Warner's (1968) study of the presumed role that introduced malaria and avian pox played in the extinction of the native Hawaiian birds is the onl,y major published work dealing with this subject. He proposed that an "imaginary line" existed at approximately 600 m, above which there were no 1 mosqui toes and be1 ow which native bi rds were not found, presumably because the,y had succumbed to introduced diseases. His findings have found wide acceptance as an example of disease limiting a host population; this despite the fact that occasional observations apuear not to demonstrate the validity of Warner's arguments. In fact, Berqer (1975) in his review rn t of this subject writes : "This is meager evidence, indeed, for the numerous assertions in the literature that the extinction of so many native forest birds was due to introduced bird diseases. It may have been so, but no trustworthy evidence has been published as of 1974." In this study we examine the species of avian malaria that are present. today in the Hawaiian Islands, the susceptibility of extant bird species to the malaria parasite, the overall percentage of wild birds infected with ma1 aria, distributional patterns of potential vectors, sporoqonic development in the vectors, and the epizootiology of malaria in the ttawaiidn Islands. We will then present kinds of evidence which show that the avian disease problem in Hawaii is much more complex than original ly proposed by Warner (1968). We shall a1 so document that malaria probably did not have a major impact upon reducing the numbers of Hawaiian birds in the late 19th century, but is presently restricting populations and affecting distributional and behavioral patterns of the native birds. Final ly, management recommendations wi 11 be suggested to minimize the present obvious probl em and assure continued heal thy avian populations. METHODS Study Areas Study areas consisted of 16 stations along two transects, established at approximately 300 m intervals on the southern and eastern slopes of Mauna Lod Volcano, Hawaii (Fiq. 1). The southern transect spanned principal ly xeric forest habitat, while the eastern transect crossed mesic forests, The dry forest was characterized by introduced tree species such as koa ha ole (Leucacena leucocephala L. ) , Chri stmas berry (Schinus terebinthifolius Raddi ) and guava (Psidium gua java L. ) at lower elevations, ohia (Metrosideros collina Forst.) with scattered mamane (Sophora chrysophyl la Sal isb. ) throughout the mid-el evation range, and predominantly niarnane in the higher parts. The wet forest habitat was .. composed of scattered ohia and numerous introduced tree species near sea level, a mixed koa (Acacia -koa Gray)-ohia forest in the mid-elevational 1' ranges, and scrub ohia at the upper elevations. A more detailed analysis of these vegetation types may he found in Mueller-Dombois and Fosberg Field Techniques From 1978-1979 wild birds were mist-netted bimonthly at each station, while at 1200 m elevation they were netted monthly over a three-year period (1978-1980). Each bird was bled b.y clipping a toe nail, a th.irl blood smear was taken, and the slide fixed for 30 sec in absolute meth,yl a1 coho1 ; before release the bird was measured and banded with unique combinations of colors, and a single USFWS metal band. Durinq August 1978, four ma1 aria-nai ve Laysan Finch (Psi tti rostra cantans) were set out at each station for a 12-da.y period. Two birds were placed in open bamboo cages within the canopy, approximately 8 m above the ground, while two controls were placed in an adjacent cage wrapped in niosqui to-proof netting. Fol lowing the exposure period a1 1 bi rds were retilrned to the laboratory and monitored for three weeks. At each station artificial mosquito oviposition sites were maintained with a constant supply of water. All sites were checked for eggs, larvae, and pupae