The Disappearance of Guam's Wildlife Gordon H. Rodda; Thomas H
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The Disappearance of Guam's Wildlife Gordon H. Rodda; Thomas H. Fritts; David Chiszar BioScience, Vol. 47, No. 9. (Oct., 1997), pp. 565-574. Stable URL: http://links.jstor.org/sici?sici=0006-3568%28199710%2947%3A9%3C565%3ATDOGW%3E2.0.CO%3B2-V BioScience is currently published by American Institute of Biological Sciences. Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/about/terms.html. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/journals/aibs.html. 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Fritts, and David Chiszar uam is an American island - - some forests were leveled by artillery near the middle of Micro- The Guam experience fire and more than 80% of the island's Gnesia, an archipelago of "mi- structures were destroyed (Morison cro" islands in the middle of the showed ecologists that 1953). After the war, the island was western Pacific Ocean. The largest extensively reseeded with an exotic island of Micronesia, Guam covers snakes can attain legume, Leucaena leucocephala, only 541 km2. It is shaped like an which permanently replaced native elongated peanut, 4 km across the densities that are trees over vast areas (Craig 1994). narrow waist and 45 km long. The As far as is known, no native bird closest larger island is Manus, which sufficient to suppress s~eciesor other vertebrates were lost is 1740 km to the south, across the as a result of this ecological upheaval equator and north of New Guinea. prey populations (Baker 1946).The ecological effects Few species are found on small, re- of the war may have been somewhat mote islands such as Guam. To reach delicate flyers, such as mosquitoes, analogous to the typhoons that natu- a land mass with levels of biodiversity fail to make the journey without rally strike Guam every few years. In comparable to what is found on con- human assistance. Indeed. Micro- 1992, for example, Guam was hit by tinents, one must travel over 2000 nesia was free of flies and mosqui- six typhoons, three of which were km south to New Guinea, west to the toes until Spanish conquistadors "super-typhoons" with sustained Philippines, or north to Japan (Fig- brought these insects to Guam winds in excess of 240 kdh. The ure 1).Neither water currents nor (Carano and Sanchez 1964). fierce storms of the western Pacific wind brings animals from those di- It is difficult to know how many denude forests and thereby select for rections, so Guam's native verte- species of animals were found on species that can tolerate severe natu- brates are limited to those species Guam before the arrival of humans, ral habitat modifications. that can fly (e.g., birds and bats), or but from archeological excavations Major changes in Guam's verte- whose eggs can ride for many weeks on the nearby island of Rota, scien- brate fauna became evident in the on small clumps of floating vegeta- tists know that the original human 1960s, when wildlife authorities no- tion (e.g., small lizards). Large colonists-or the domestic animals ticed that birds were entirelv absent nonvolant vertebrates and even small that the colonists brought with from the southern one-third of the them-extirpated many species thou- island and that the boundary of Gordon H. Rodda is a zoologist, and sands of years ago. On Rota, as on birdlessness seemed to be creeping Thomas H. Fritts is chief of the Biological Hawaii, approximately half of the steadily northward. By the end of the Survey Program, at the Patuxent Wildlife native birds were exterminated by 1970s, birds were missing from the Research Center, Biological Resources Di- prehistoric humans (Steadman southern two-thirds of the island vision, United States Geological Survey, 1995);presumably, Guam lost a simi- (Engbring 1983, Jenkins 1983). By National Museum of Natural History, lar number. But following that spate 1985, most of the bird species were Washington, DC 20560. They study tropi- of prehistoric extinctions, the native either isolated in small pockets at the cal reptiles and the effects of species trans- wildlife community remained rela- northern tip of the island or were locations. David Chiszar is a professor in the Department of Psychology, University tively stable until the 1960s. Surpris- completely gone (Figure 2). of Colorado, Boulder, CO 80309-0345. ingly, the island's fauna was little What was killing the birds? Two His interests revolve around the behavior disrupted by the savage fighting of theories generated particular inter- of reptiles, especially the feeding adapta- World War I1 (Engbring and Pratt est. One was that pesticides, which tions of snakes. O 1997 American Insti- 1985), which subjected Guam to had been used in large amounts after tute of Biological Sciences. naval bombardment so severe that World War I1 to control mosquitoes, October 1997 565 The snake turned out to be respon- sible for not only the extinctions of the birds, but also the decimation of the island's lizards (Figure 4; Rodda and Fritts 1992b), mammals (Wiles 1987), and domestic animals (Fritts and McCoid 1991). When Savidge reported her discovery at a meeting of the American Ornithologists' Union in 1983, she met with skepti- cism from some members of the au- - GUAM .-. dience. Marshall (1985) noted that "Few could believe that a mere snake was that efficient a predator and could build up the numbers com- mensurate with such devastation" (p. 260). One commentator responded to Savidge's conclusion by devoting a column to promoting the pesticide . hypothesis (Diamond 1984). .. The fact that Savidge's conclusion I was initially rejected but is now \ ** widely accepted, reflects the growth of ecology. How do we know that the snake caused the extirpations? Six lines of evidence point to the brown tree snake as the primary cause of Guam's avifauna extinctions CJ (Savidge 1987): the geographic pat- B tern of bird losses mirrored the si- multaneous population expansion of Figure 1. Guam is the largest of the more than 2100 tiny islands of Micronesia (most the snake (that is, the snake spread are too small to be seen in this view). Lying north of the equator near the middle of the northward across Guam on approxi- western Pacific Ocean, Guam is roughly equidistant (over 2000 km) from Japan, the mately the same schedule as bird Philippines, and New Guinea. distributions retreated to Guam's north end); the snake is an efficient had poisoned the birds, as DDT had cally through the bird populations, predator of the species that declined; done to some birds in mainland North perhaps carried by the introduced there is little or no evidence for alter- America. The second, and leading, mosquitoes. An avian pathologist, Julie nate causes of declines, such as pes- hypothesis was that an introduced bird Savidge, was hired by Guam's Divi- ticides, habitat destruction, diseases, disease, such as had ravaged the birds sion of Aquatic and Wildlife Resources or environmental contaminants; all of Hawaii (van Riper et al. 1986, War- to find the disease that was killing the bird species were affected, including ner 1968), had spread catastrophi- birds of Guam. In collaboration with both native and introduced species other pathologists (thus, the natives did not retreat in and pesticide spe- response to expansion of introduced cialists, she scoured species); the brown tree snake is un- the forests and birds expectedly common on Guam; and of Guam for evi- no comparable bird extirpations were dence of this dis- observed on similar nearby islands ease, but she came that lacked the snake. up empty-handed For many of the skeptics, the evi- (Grue 1985, Sav- dence that the brown tree snake is idge 1987, Savidge unexpectedly common on Guam was et al. 1992). She the clincher. Counting snakes is concluded instead tough. They are notoriously difficult that the acciden- to spot (Rodda 1993),and the brown tally introduced tree snake is particularly hard to find brown tree snake, because it is nocturnal and arboreal. Boiga irregularis, It moves slowly through the foliage Figure 2. These fairy terns are among the 12 bird species (both Was responsible at night, looking and often acting land and sea birds) that have disappeared from Guam in the for the loss of the like a drab vine. Few visitors to Guam wake of the introduction of the brown tree snake. birds (Figure 3). ever see a snake. However, our mark- BioScience Vol. 47 No. 9 recapture and trapping By October 1996, only 3 studies suggest that the of Guam's 12 native forest snake achieved peak densi- bird species still survived in ties on Guam of approxi- the wild.