The Scientific Bases for PRESERVATION of the MARIANA CROW

Committee on the Scientific Bases for the Preservation of the Mariana Crow

Commission on Life Sciences

NATIONAL RESEARCH COUNCIL

NATIONAL ACADEMY PRESS
Washington, D.C. 1997



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The Scientific Bases for Preservation of the Mariana Crow The Scientific Bases for PRESERVATION of the MARIANA CROW Committee on the Scientific Bases for the Preservation of the Mariana Crow Commission on Life Sciences NATIONAL RESEARCH COUNCIL NATIONAL ACADEMY PRESS Washington, D.C. 1997

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The Scientific Bases for Preservation of the Mariana Crow NATIONAL ACADEMY PRESS 2101 Constitution Ave., N.W. Washington, D.C. 20418 NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. In preparing its report, the committee invited people with different perspectives to present their views. Such invitation does not imply endorsement of those views. This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Harold Liebowitz is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given even to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce Alberts and Dr. William A. Wulf are chairman and interim vice chairman, respectively, of the National Research Council. This study by the National Research Council's Commission on Life Sciences was sponsored by the US Department of the Interior Fish and Wildlife Service under cooperative agreement no. 14-0001-48-96520. Points of view in this document are those of the authors and do not necessarily represent the official position of the US Department of the Interior. Library of Congress Catalog Card Number 96-70149 International Standard Book Number 0-309-05581-4 Additional copies of this report are available from: National Academy Press 2101 Constitute Ave., NW Box 285 Washington, DC 20055 800-624-6242 202-334-3313 (in the Washington Metropolitan Area) http://www.nap.edu Copyright 1997 by the National Academy of Sciences. All rights reserved. Printed in the United States of America

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The Scientific Bases for Preservation of the Mariana Crow COMMITTEE ON THE SCIENTIFIC BASES FOR THE PRESERVATION OF THE MARIANA CROW W. DONALD DUCKWORTH, Chair, Bishop Museum, Honolulu, Hawaii STEVEN R. BEISSINGER, University of California, Berkeley SCOTT R. DERRICKSON, National Zoological Park, Front Royal, Virginia THOMAS H. FRITTS, National Biological Service, Washington, DC SUSAN M. HAIG, Oregon State University, Corvallis FRANCES C. JAMES, Florida State University, Tallahassee JOHN M. MARZLUFF, Sustainable Ecosystems Institute, Meridian, Idaho BRUCE A. RIDEOUT, Center for Reproduction of Endangered Species, San Diego, California NRC Staff ERIC A. FISCHER, Board Director TANIA WILLIAMS, Study Director PAULETTE A. ADAMS, Project Assistant JEFFREY PECK, Project Assistant

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The Scientific Bases for Preservation of the Mariana Crow BOARD ON BIOLOGY MICHAEL T. CLEGG, Chair, University of California, Riverside, California JOHN C. AVISE, University of Georgia, Athens DAVID EISENBERG, University of California, Los Angeles GERALD D. FISCHBACH, Harvard Medical School, Cambridge, Massachusetts DAVID J. GALAS, Darwin Technologies, Seattle, Washington DAVID V. GOEDDEL, Tularik, Inc., San Francisco, California ARTURO GOMEZ-POMPA, University of California, Riverside COREY S. GOODMAN, University of California, Berkeley BRUCE R. LEVIN, Emory University, Atlanta, Georgia OLGA F. LINARES, Smithsonian Tropical Research Institute, Miami, Florida ELLIOTT M. MEYEROWITZ, California Institute of Technology, Pasadena ROBERT T. PAINE, University of Washington, Seattle RONALD R. SEDEROFF, North Carolina State University, Raleigh DANIEL SIMBERLOFF, Florida State University, Tallahassee ROBERT R. SOKAL, State University of New York, Stony Brook SHIRLEY M. TILGHMAN, Princeton University, Princeton, New Jersey RAYMOND L. WHITE, University of Utah, Salt Lake City Staff: ERIC FISCHER, Director KATHLEEN BEIL, Administrative Assistant JANET JOY, Program Officer JEFFREY PECK, Project Assistant TANIA WILLIAMS, Program Officer

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The Scientific Bases for Preservation of the Mariana Crow COMMISSION ON LIFE SCIENCES THOMAS D. POLLARD, Chair, Johns Hopkins University, Baltimore, Maryland FREDERICK R. ANDERSON, Cadwalader, Wickersham & Taft, Washington, DC JOHN C. BAILAR III, University of Chicago, Illinois JOHN E. BURRIS, Marine Biological Laboratory, Woods Hole, Massachusetts MICHAEL T. CLEGG, University of California, Riverside GLENN A. CROSBY, Washington State University, Pullman URSULA W. GOODENOUGH, Washington University, St. Louis, Missouri SUSAN E. LEEMAN, Boston University, Massachusetts RICHARD E. LENSKI, Michigan State University, East Lansing THOMAS E. LOVEJOY, Smithsonian Institution, Washington, DC DONALD R. MATTISON, University of Pittsburgh, Pennsylvania JOSEPH E. MURRAY, Wellesley Hills, Massachusetts EDWARD E. PENHOET, Chiron Corporation, Emeryville, California EMIL A. PFITZER, Research Institute for Fragrance Materials Inc., Hackensack, New Jersey MALCOLM C. PIKE, University of Southern California, Los Angeles HENRY C. PITOT, III, University of Wisconsin, Madison JONATHAN M. SAMET, Johns Hopkins University, Baltimore, Maryland HAROLD M. SCHMECK JR, 32 Seapine Road, North Chatham, Massachusetts CARLA J. SHATZ, University of California, Berkeley JOHN L. VANDEBERG, Southwest Foundation for Biomedical Research, San Antonio, Texas Staff: PAUL GILMAN, Executive Director SOLVEIG PADILLA, Administrative Assistant

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The Scientific Bases for Preservation of the Mariana Crow Preface The unique and fragile nature of environments found in oceanic island systems is well known. Through colonization and evolution, these relatively small land areas have evolved unique biota characterized by small populations, rare forms, and low phylogenetic diversity. They are also exceedingly vulnerable to human disturbance and to invasions of introduced species. Thus, while this report focuses on the challenges posed by preserving one species, the aga (or Mariana crow), it reflects the larger issues and challenges of biodiversity conservation in all oceanic island ecosystems. The Mariana archipelago is the most northerly island group in Micronesia, lying roughly equidistant from Japan to the north, New Guinea to the south, and the Philippines to the west. Consisting of a north-south chain of 15 islands that extends over 675 km, the Marianas are in reality the emergent portions of a mighty mountain range that rises from the deepest portion of the Pacific Ocean, the Mariana Trench. The islands are volcanic in origin and generally diminish in size from south to north. The warm humid climate is distinguished by relatively constant temperature, wet and dry seasons, and a high annual probability of typhoons during the wet season. The native ecosystems of the archipelago have been in decline since the earliest colonization by humans. Habitat destruction and alteration have been especially severe during this century as a result of war, post-war development, and associated intentional or accidental introduction of predatory or competitive species, especially on Guam. While these factors have impacted all groups of native organisms in the Mariana Islands to one degree or another, the extinction or near extinction of nearly all the native forest birds on Guam, most certainly linked to

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The Scientific Bases for Preservation of the Mariana Crow the large population of the introduced brown tree snake, is by far the most significant and alarming. The rapid decline of the aga is another painful reminder of the importance and challenge of preserving the unique environmental heritage of these islands, the need for increased knowledge to restore and maintain native species and habitats, and the compelling and lasting value of extensive public education to stimulate environmentally informed public policy development. In response to a request from the US Fish and Wildlife Service (FWS), the National Research Council's Board on Biology established the Committee on the Scientific Bases for the Preservation of the Mariana Crow (aga) in March 1996. Its task was to review the existing data pertaining to the aga while focusing on several scientific issues: Assess to the extent possible the causes of the continuing decline in populations of the aga in the wild; Evaluate options for action to halt or reverse the decrease in numbers of the aga; Estimate the minimum viable population for survival of the Guam population of this species; and Evaluate the advisability of adding genetic material from the Rota population to the Guam population. Current options for the recovery of the aga populations vary; they range from continuing present management strategies to a variety of translocations of one or both populations. From the assembled data and their evaluation, the committee has developed a set of recommendations designed to assist interested parties in working effectively to aid the recovery of the aga. The committee held three meetings: one in Hawaii (Honolulu, April 1996); one in Guam and Rota (May 1996); and one at the Arnold and Mabel Beckman Center in Irvine, California (June 1996). The committee collected and reviewed data on the aga from biologists in federal, state, territorial, and commonwealth agencies, and other scientists and individuals. Members visited the 'alala (Hawaiian crow) recovery project on the island of Hawaii during the first meeting, and we are grateful to Cynthia Salley, McCandless Ranch, the FWS, and the Peregrine Fund for facilitating that opportunity. In Guam, the committee visited the laboratories and rearing facilities of both federal and Guam agencies and was extensively briefed both in field locations and formal settings. On Rota, nesting sites were observed and a broad range of aga habitat was visited through the support and generosity of Stan Taisacan of the Commonwealth of the Northern Mariana Islands Department of Lands and Natural Resources Division of Fish and Wildlife, and Dan Grout of FWS. The information and support provided by those people and many others were invaluable to the committee and to the development of this report. In addition, we are grateful to the many other persons and organizations who assisted the committee in preparing this report (See appendix B).

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The Scientific Bases for Preservation of the Mariana Crow From the outset of this study, the committee has been constantly motivated to produce a report in a time-frame that would allow for consideration of its recommendations by the FWS and related agencies for implementation during this year's breeding season. Consequently, the committee schedule was fast-paced and intensive, but never at the expense of limiting the fullest measure of discussion and evaluation of available data in reaching consensus. It was my pleasure and privilege to work with a talented, enthusiastic, and dedicated committee. This report is the product of their hard work and spirited, yet always collegial, debate. I want to express my deepest gratitude for their patience, their insight, and their generosity in response to the rigorous schedule and scientific challenges imposed by the task. Last, on behalf of the entire committee, I want to express our gratitude to the National Research Council staff for the vital role they played in all aspects of the study. The dedication and persistence of project director Tania Williams facilitated and expedited the committee's activities throughout the study. In addition, Paulette Adams and Jeff Peck provided support for our various activities. W. Donald Duckworth, Chair Committee on the Scientific Bases for the Preservation of the Mariana Crow September 1996

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The Scientific Bases for Preservation of the Mariana Crow Contents     EXECUTIVE SUMMARY   1 1   INTRODUCTION   5     Distribution and Abundance   5     Legal Status   6     Genetics   8     This Study   8 2   HISTORY   11     Description of Guam and Rota   11     Ecological History and Faunal Change   15     Natural History of the Aga   19     Comparison with the 'Alala   21     Demography of the Aga   21     Possible Causes of Population Declines   26     Population Projection for the Aga on Guam   31     Past and Current Conservation and Management   31

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The Scientific Bases for Preservation of the Mariana Crow 3   BROWN TREE SNAKE   39     Natural History   39     Effects of the Presence of the Brown Tree Snake on Guam   42     Decline of Birds on Guam in Relation to the Brown Tree Snake   45     Efforts to Control the Brown Tree Snake on Guam   46     Prognosis for Control on Guam   50     Threat of Spread of the Brown Tree Snake to Other Islands   50 4   MAJOR FINDINGS AND CRITERIA FOR RECOVERY OF THE AGA   53     Summary of Major Findings   53     Criteria for Prioritizing Aga Recovery Actions   57 5   OPTIONS FOR THE MANAGEMENT OF THE AGA   59     Cessation of Management   59     Continuation of Present Management Strategy   59     Intensive Management   60     Translocation Options   62 6   ELEVEN RECOMMENDED MANAGEMENT ACTIONS FOR RECOVERY AND THEIR RATIONALE   67     Recommendation 1   67     Recommendation 2   69     Recommendation 3   70     Recommendation 4   70     Recommendation 5   71     Recommendation 6   71     Recommendation 7   72     Recommendation 8   72     Recommendation 9   72     Recommendation 10   73     Recommendation 11   73     REFERENCES   75     APPENDIX A: STATEMENT OF TASK   87     APPENDIX B: ACKNOWLEDGMENTS   88     APPENDIX C: COMMITTEE AND STAFF BIOGRAPHICAL INFORMATION   90