Censusing Laysan Ducks Anas laysanensis: a lesson in the pitfalls of estimating threatened species populations | Bird Conservation International | Cambridge Core (original) (raw)

Summary

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the 'Save PDF' action button.

The Laysan Duck Anas laysanensis is a threatened species endemic to Laysan Island, Hawaü U.S.A., with a population that appears subject to severe fluctuation, although this may be attributable to different census methods. The most effective method used so far has been one that notes the ratio of marked to unmarked birds seen on censuses conducted at dusk around the central lake. In 1986 and 1987, weekly censuses were made from which population estimates were derived with the Lincoln—Petersen Index: the current population is approximately 500. The ducks were least visible during the nesting and moulting periods of spring and summer, and population estimates were significantly lower during that period in both 1986 and 1987. This phenomenon calls in doubt other estimates and probably accounts for the fluctuations noted in previous years. Thus careful attention should be given to potential problems in monitoring threatened species populations, because without a clear understanding of the ecology of the threatened species, population estimates could suggest inappropriate management measures.

References

Bailey, A. M. (1919) Notes on our Hawaüan reservation. Natural History 19: 382–395.Google Scholar

Bailey, A. M. (1956) Birds of Midway and Laysan Islands. Denver Mus. Nat. Hist., Mus. Viet. 12.Google Scholar

Berger, A. J. (1970) The present status of the birds of Hawaü. Pacific Sci. 24: 29–42.Google Scholar

Berger, A. J. (1972) Hawaüan birdlife. Second edition. Honolulu: University Press of Hawaii.Google Scholar

Caspers, H. (1967) Biology of a hypersaline lagoon in a tropical atoll island (Laysan). Pp. 326–333 in Misra, R. and Gopal, B., eds. Proceedings of the symposium on recent in tropical ecology. Varanasai, India: The International Society for Tropical Ecology.Google Scholar

Davis, D. E. and Winstead, R. L. (1980) Estimating the numbers of wildlife populations. Pp. 221–245 in Schemnitz, S. D., ed. Wildlife management techniques manual. Fourth edition, revised. Washington, D.C.: The Wildlife Society.Google Scholar

Ely, C. A. and Clapp, R. B. (1973) The natural history of Laysan Island, northwestern Hawaüan Islands. Atoll Res. Bull. 171: 1–361.CrossRefGoogle Scholar

Fisher, W. K. (1903) Birds of Laysan and the leeward islands, Hawaüan group. Bull. U.S. Fish Commission 23: 767–807.Google Scholar

Halliday, T. (1978) Vanishing birds: their natural history and conservation. London: and Jackson.Google Scholar

Johnsgard, P. A. (1978) Ducks, geese and swans of the world. Lincoln, Nebraska: University of Nebraska Press.Google Scholar

Kear, J. (1977) The problems of breeding endangered species in captivity. Internatn. Zoo Yearbook 17: 5–14.CrossRefGoogle Scholar

Kear, J. and Williams, G. (1978) Waterfowl at risk. Wildfowl 29: 5–21.Google Scholar

Lack, D. (1970) The endemic ducks of remote islands. Wildfowl 21: 5–10.Google Scholar

Lamoureux, C. H. (1963) The flora and vegetation of Laysan Island. Atoll Res. Bull. 97: 1–14.CrossRefGoogle Scholar

Lamoureux, C. H. (1985) Restoration of native ecosystems. Pp. 421–431 in Stone, C. P. and Scott, J. M., eds. with assistance of Stone, D. B. and Komenaka, A. R.. Hazvaíi's terrestrial ecosystems: preservation and management. Honolulu: University of Hawaü.Google Scholar

Moulton, D. W. and Weller, M. W. (1984) Biology and conservation of the Laysan Duck (Anas laysanensis). Condor 86: 105–117.CrossRefGoogle Scholar

Munro, G. C. (1944) Birds of Hawaü. Honolulu: Tongg Publishing Company.Google Scholar

Ripley, S. D. (1960) Laysan teal in captivity. Wilson Bull. 72: 244–247.Google Scholar

Sincock, J. L. and Kridler, E. (1977) The extinct and endangered endemic birds of the northwest Hawaüan Islands. Unpublished (118 pp.).Google Scholar

Todd, F. S. (1979) Waterfowl: ducks, geese and swans of the world. San Diego: Sea World Press.Google Scholar

U.S. Fish and Wildlife Service (1982) The Laysan Duck recovery plan. Portland, OR.Google Scholar

U.S. Fish and Wildlife Service (1983) Recovery plans for Laysan Duck, Sonoran prong-horn approved. Endangered Species Techn. Bull. 8: 6.Google Scholar

Weller, M. W. (1980) The island waterfowl. Ames, Iowa: Iowa State University Press.Google Scholar

Zimmerman, D. R. (1970) To save a bird in peril. New York: Coward, McCann and Geoghegan.Google Scholar