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Wildlife Damage Management Conferences -- Wildlife Damage Management, Internet Center Proceedings for

2005

Challenges of Invasive and

William Pitt USDA, APHIS, Wildlife Services, National Wildlife Research Center, Hilo, HI, USA

Daniel Vice USDA, APHIS, Wildlife Services, Barrigada Heights, , USA

Mike Pitzler USDA, APHIS, Wildlife Services, Honolulu, HI, USA

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Pitt, William; Vice, Daniel; and Pitzler, Mike, "Challenges of Invasive Reptiles and Amphibians" (2005). Wildlife Damage Management Conferences -- Proceedings. 84. https://digitalcommons.unl.edu/icwdm_wdmconfproc/84

This Article is brought to you for free and open access by the Wildlife Damage Management, Internet Center for at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Wildlife Damage Management Conferences -- Proceedings by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. CHALLENGES OF INVASIVE REPTILES AND AMPHIBIANS

WILLIAM C. PITT, USDA, APHIS, Wildlife Services, National Wildlife Research Center, Hilo, HI, USA DANIEL S. VICE, USDA, APHIS, Wildlife Services, Barrigada Heights, Guam, USA MIKE E. PITZLER, USDA, APHIS, Wildlife Services, Honolulu, HI, USA

Abstract: Although worldwide distributions of many amphibians and reptiles are declining, a handful of are spreading rapidly throughout tropical regions of the world. The species that have the greatest effect tend to be generalist feeders, have high reproductive rates, attain large population sizes, and often due to their behavior and or small size, are easily transported or are difficult to detect. The most notable of these species include the coqui , cane , bullfrog, brown tree , and Burmese pythons. The effect of a few individuals typically is small but the combined effect of large populations can be devastating to ecological communities and agriculture. Currently, there are few methods available to effectively remove established populations. However, management capabilities are developing, with more effective methods in detecting incipient populations, improved control methods, more stringent restrictions on movement of nonnative , and increased public support.

Key words: amphibians, , bullfrog, Burmese pythons, , coqui frog, invasive species, reptiles

Proceedings of the 11th Wildlife Damage Management Conference. (D.L. Nolte, K.A. Fagerstone, Eds). 2005

INTRODUCTION movement in transportation networks. In the last 20 years, worldwide declines of These cryptic behaviors also allow the many and reptiles have been well development of incipient populations that documented. At the same time, a growing are difficult to detect until the is well number of species have invaded new established. Species that exhibit all of these habitats and have reached population levels attributes tend to be most successful at that have had negative consequences on colonizing new environments . native flora and fauna, agriculture, and local The probability of a successful economies (Mooney and Hobbs 2000). Five invasion is also dependent on the qualities of of the 24 vertebrate species listed as the the ecosystem invaded (Simberloff and Von worst invasive species are amphibians and Holle 1999). Beyond a suitable climate and reptiles (Lowe et al. 2004). Invasive habitat, ecosystems with a limited amphibians and reptiles generally have a assemblage of resident species have fewer high reproductive rate, which facilitates potential competitors and predators and, rapid population growth and recovery from therefore, enhanced probability of successful stochastic events. They have generalized colonization. Lastly, as the frequency of diets that effectively utilize locally abundant invasion events by a species increases, the resources. Typically, successful invaders are likelihood that the species will successfully small or secretive, which allows undetected establish increases. Insular areas are

112 generally more susceptible than mainland Species smuggled and released for the pet areas, as islands support few predators or trade are increasing threats, especially in competitors, often receive heavy air and sea tropical environments and difficult to traffic, and typically provide a favorable prevent as border security measures and the climate for many potentially invasive realignment of customs inspections are not species (Elton 1958, Simberloff 1995). focused on invasive species. Currently, 33 non-native amphibians and reptiles have been established in and HIGHLIGHTED SPECIES more species continue to arrive (M. Several species have become widely Wilkinson, Hawaii Department of Land and publicized for their overall effect as invasive Natural Resources, personal species or as successful invaders in multiple communication). For example, six snake regions. To understand the effects of species have been intercepted in invasive amphibians and reptiles and transportation networks in the Pacific and at potential problems with control efforts, we least six species of have established provide a brief summary of several populations in Guam in the past three years noteworthy species. Further, we provide a (D. Vice, personal communication). While brief discussion regarding the social, the mechanism for arrival differs among biological, and political complexity of the locales and species, the rapid and expanding invasive species issue. colonization of invasive reptiles and amphibians is affecting ecological and Coqui Frogs economic systems worldwide. The coqui frog (Eleutherodactylus The pathways that transport invasive coqui) was introduced into Hawaii during species are varied and likely increasing. 1988-1995, likely from infested plant Rapid increases in global transportation shipments from (Kraus et al. networks move people and commodities to 1999). Sizeable populations are now found previously remote destinations, increasing on the islands of Hawaii, Maui, Oahu, and the homogeneity of global floral and faunal Kauai. The super-abundant terrestrial frog communities (Mack et al. 2000). Generally, threatens Hawaii’s multi-million dollar species are either accidentally or floriculture, nursery, real estate, and tourist intentionally transported. Accidental industries, as well as its unique ecological movements include stowaways in air and sea systems (Beard and Pitt 2005). Effects from cargo, shipping containers that holds cargo, the coqui are predominantly associated with or vessels that move people and the frog’s piercing call (80-90 dBA at 0.5 m) commodities (e.g., brown treesnake), and the extremely high population densities hitchhikers on agricultural products (e.g., that have exceeded 50,000 individuals ha in coqui frogs, geckos, blind ) and pet Hawaii. Beyond the noise nuisance, the escapes (e.g., pythons and Jackson loud nighttime choruses of male frogs has chameleons). Intentional releases include affected real estate values, as people desire those that were intended to provide food for coqui free property (A. Hara, University of people (e.g., bullfrogs and turtles), to Hawaii, unpubl. data). The floriculture combat other species (e.g., cane and industry may also be affected through the poison dart frogs), or for aesthetic reasons refusal of export shipments, reduced sales, (e.g., veiled chameleons). Although many and increased costs associated with control intentional releases are altruistic in intent, and quarantine efforts. Further, the frogs some are for insidious or financial reasons. may affect native insect populations, forest

113 nutrients, compete with native and potential phytotoxicity to plants, high costs , and alter ecosystem processes (Beard associated with repetitive spraying of large and Pitt 2005). Due to the high densities of areas, access to remote or private land, and frogs and their present range, few options other factors (Pitt and Sin 2004b). exist for control of wild populations. Mechanical controls include hand capturing, Burmese Pythons habitat alteration, and trapping. These Burmese pythons (Python molurus methods have limited effectiveness, as the bivittatus) became established in Everglades logistic constraints in applying across a National Park during the 1990s as the result large, complex environment with heavy frog of unwanted or accidentally released pets (S. populations preclude large-scale application. Snow, National Park Service, pers. comm.). Some success has been documented using Burmese pythons, native to Southeast Asia, hot water treatments for quarantine efforts in are large snakes (>7 m) with high ornamental plant shipments (M. Wilkinson, reproductive rates and are common pets in pers. comm.). Biological control or the the United States (Pough et al. 1998). release of organisms to combat the frog Pythons may compete with native snake likely will have little success and could have species, prey on many native mammals and many unintended consequences. birds, transmit disease to native reptiles, and Unfortunately, disease organisms have a low disturb visitors due to their large size. The potential for controlling coqui frogs in number of snakes removed has quickly Hawaii, primarily because viruses and increased in recent years and may represent diseases are most effective when applied to a rapidly increasing population (S. Snow, small populations of species with low unpubl. data.). Sources of mortality for the reproductive capacity (Brauer and Castillo- snakes in the Park include motor vehicles, Chavez 2001, Daszak et al. 2003). In large mowing equipment, fire, and possibly populations, diseases may induce temporary alligators (S. Snow, unpubl. data). Currently, population declines, but surviving management actions center on direct control individuals may develop resistance, and education efforts to prevent further resulting in population levels similar to introductions. Control techniques include those pre-treatment. As most of the major trapping, hand capture, and early detection frog diseases infect stages (Daszak using dogs. et al. 2003), coqui, which develop directly into tiny frogs inside terrestrially-deposited Bullfrogs , are less likely to be affected by disease Bullfrogs (Rana catesbeiana) from organisms. Although many frogs are quite the eastern United States were widely susceptible to a variety of chemicals, the introduced from 1900-1940 into many terrestrial coqui frog has been unaffected by western states, including Hawaii, as a food a wide range of potential pesticides. resource. Bullfrogs are responsible for Currently, only citric acid and hydrated lime significant ecological effects and have been have proven to be effective and registered difficult to control as they are highly mobile, for use to combat the frogs (Pitt and Sin exhibit generalized eating habits, and have 2004a, Pitt and Doratt 2005). Although high reproductive capacity (Moyle 1973). these chemicals are effective if sprayed Bullfrogs may cause the extirpation of other directly on the frogs, there are limitations species due to intense and with these products, including varying competition (Kats and Ferrer 2003), and efficacy affected by weather conditions, may be a primary predator of several

114 federally endangered waterbirds in Hawaii. population levels (> 20 per acre) on Guam, Management of bullfrog populations is in part because of abundant food and the difficult, in part due to commingling with lack of predators and ecological competitors. native species in aquatic habitats. Adult The extreme densities of BTS have resulted frogs are removed by trapping or hand in the extirpation of most of Guam’s native captures and are destroyed by forest birds (9 of 11), reductions in native draining ponds or chemical treatment with populations, and extirpation of two of limited success. Fencing may also be used the three native bats (Savidge 1988, Rodda to limit frog movements away from infested and Fritts 1992, Vice et al. 2005b). Beyond habitats. the severe ecological effects, brown treesnakes threaten human health and safety, Cane Toads agriculture, poultry production, and pets.. Giant neotropical ( marinus) or The snakes are poisonous and may cause cane toads were widely introduced from trauma to small children, with numerous into sugar cane producing bites treated by medical facilities annually regions worldwide to control beetles causing (Fritts et al. 1994). The largest economic damage to crops (McKeown 1978). impact from the snakes is the disruption of However, the effort had very limited power systems. The aboreal snake success, as the beetles could climb into the frequently climbs utility poles, power lines, vegetation to escape foraging toads. Cane and other structures, searching for birds and toads may compete with native species for . Snakes occasionally disrupt these food, compete with native amphibians for systems when they cross from grounded to breeding sites, and prey on a variety of live structures, causing an estimated 1.4 and vertebrate species (McCoid million (U.S. dollars) in damages from 1995, Catling et al. 1999, Williamson 1999, power outages (Fritts et al. 1999). The Boland 2004). Further, native species cryptic, nocturnal snake is especially adept preying on cane toads may be poisoned by at stowing in cargo and dispersing off Guam the toad’s parotoid glands (McCoid 1995). via commercial and military traffic (Vice The frogs also may be a nuisance when large and Vice 2004), creating substantial risk to numbers congregate for breeding in ponds or surrounding islands. A variety of methods water features and may foul water sources. are employed to control snakes and restrict has been aggressively pursuing their access to aircraft and cargo leaving the control options but has had little success in islands, including hand capture off fences developing effective methods (Luntz 1998). (Engeman and Vice 2001), trapping (Vice et Currently, the only effective strategies are al. 2005a), and inspection of outbound cargo pond drying, hand capture, and trapping. using detector dogs (Vice and Engeman 2000, Vice and Pitzler 2002) . Other Brown Treesnakes developing and potential methods include Brown treesnakes ( irregularis; the use of oral toxicants, repellents, BTS) were accidentally introduced into reproductive inhibition, and barriers. Guam shortly after World War II from their native range in Australia and Papua New Curious Skink Guinea. The slender arboreal snakes average Often the effects of invasive species approximately 1 m in length, with large are not predictable, and the combined effects individuals capable of exceeding 2.5 m. of two or more invasive species may result They have reached extremely high in synergistic effects that exceed the sum of

115 the individual species effects. Such is the PRIORITIES OF INVASIVE SPECIES case of the curious skink (Carlia The priorities of invasive species ailanpalai), skink, a small terrestrial lizard management are generally divided between that was introduced to Guam in the 1960s prevention and control. Prior to (Zug 2004). This lizard has reached establishment, research and funding should extremely high population densities, go to prevention and early detection to (approaching 10,000 acre in snake-free decrease the potential for species becoming areas) on Guam both in forested habitats and a problem. To increase the effectiveness of near human habitation (Campbell 1996). limited funding, a risk analysis should be Due to sheer number of lizards, they may performed to promote awareness of species compete with native lizards for food and that could cause significant effects. Further, physically displace other native terrestrial coordination and cooperation among state skinks through territorial interactions. and local agencies decreases the potential However, this is only a small part of the for duplicated efforts and increases the overall effect on Guam. The high response efforts for incipient species. After population levels of the lizards have a species has become established, research exacerbated other problems, as the skink and funding is shifted to documenting serves as the primary food source supporting effects of the species on ecological services, the abundant BTS population on island. The agriculture, and local economies. abundance of skinks in close proximity to Development of control strategies and human habitation brings snakes into contact public awareness area are priorities after with cargo facilities, power generation and establishment to control the effects of the distribution stations, and agricultural new species. production, increasing the risk of snake- It is widely accepted that prevention caused damages associated with these is the preferred means of dealing with activities. The invasive skink has now invasive species, as post-colonization colonized the remainder of the populated eradication efforts require massive funding , and may increase and resource commitments. Additionally, the probability of successful colonization by complete eradication of vertebrate species the BTS, as the skink will provide an has rarely been accomplished in large abundant ectothermic food source for landscapes. Unfortunately, the line that juvenile snakes, should they reach the separates the priorities before and after currently snake-free islands. Further, the establishment dictates the amount of funding skink population has facilitated growth in available and the cost of the eradication Guam’s population of native yellow bittern effort. Prior to species establishment, the (Ixobrychus sinensis). Increasing bittern cost of controlling a species is low and the populations near Guam’s airport has created probability of success is high. However, the an aviation safety risk, as bitterns frequently amount of funding and public interest in forage for skinks in the manicured turf dealing with the potential problem is around the airfield and are subsequently generally low at this time. Federal funding struck by aircraft (Vice and Pitzler 1999). for research and interdiction efforts prior to Thus, a small invasive species with few species establishment is typically not a part predictable effects may cause a myriad of of congressional funding. Funding for significant emergent effects. research and interdiction efforts is usually only secured with public support and congressional backing. After the species is

116 established, funding typically becomes more effective approach to invasive species available and public interest in dealing management is to secure funding for increases. Conversely, the costs of control research and interdiction efforts to prevent and/or eradication efforts sky rocket and the establishment. probability of successful eradication drops after a species is established. This same LITERATURE CITED scenario has been repeated in many areas BEARD, K.H., AND W.C. PITT. 2005. with many species. A recent example is the Ecological consequences of the coqui above-mentioned case of the coqui frog in frog invasion in Hawaii. Diversity and Hawaii. Although the species became Distributions: In press. established by the early 1990s in parts of BOLAND, C.R.J. 2004. Introduced cane toads Bufo marinus are active nest predators some islands, no funding was available, and competitors of rainbow bee-eaters even though the potential to eradicate was Merops ornatus: Observational and still high. The primary public opinion was experimental evidence. Biological that this was not a major problem and there Conservation 120:53-62. were likely to be few negative consequences BRAUER, F., AND C. CASTILLO-CHAVEZ. 2003. associated with this introduction. Ten years Mathematical models in population later, public opinion is extremely supportive biology and epidemiology. Texts in of dealing with the issue and several studies applied mathematics. Springer Verlag, have documented the effects of the frogs on New York, NY, USA. ecological communities, real estate, CATLING, P., A. HERTOG, R. BURT, J. WOMBEY, agriculture, and human health (Kraus and AND R. FORRESTER. 1999. The short- term effect of cane toads (Bufo marinus) Campbell 2002). To highlight this change, in on native fauna in the Gulf Country of March 2004, the Mayor on the island of the . Wildlife Hawaii declared a state of emergency in Research 26:161-185. dealing with the coqui situation. CAMPBELL, E.W., III. 1996. The effect of Unfortunately, this response occurred once brown tree snake (Boiga irregularis) the frog had populated massive tracts of predation on the island of Guam’s extant habitat on the island, rendering eradication lizard assemblages. PhD Dissertation, unlikely. Ohio State University, Columbus, OH, In conclusion, invasive amphibians USA. and reptiles are an increasing worldwide DASZAK, P., A.A. CUNNINGHAM, AND A.D. problem, causing a diverse array of HYATT. 2003. Infectious disease and amphibian population declines. problems that cannot be easily predicted. Diversity and Distributions 9:141-150. Invasive reptiles and amphibians may cause ELTON, C.S. 1958. The ecology of invasions by more significant problems on island systems animals and plants. Methuen and Co., than mainland areas. The number of new Ltd., London, United Kingdom. introductions is likely to continue escalating, ENGEMAN, R.M., AND D.S. VICE. 2001. as many pathways of invasion are not Objectives and integrated approaches subject to stringent quarantine and/or for the control of brown treesnakes. control. Currently, there are few effective Integrated Pest Management Reviews options in controlling established invasive 6:59-76. and amphibian species, and the cost FRITTS, T.H., AND D. CHIZAR. 1999. Snakes on for control efforts is often extreme once a electrical transmission lines: Patterns, causes, and strategies for reducing species becomes widespread. Although electrical outages due to snakes. Pages politically challenging, the most cost 89-103 in G.H. Rodda, Y. Sawai, D.

117 Chizar, and H. Tanaka, editors. National Biological Service, Problem snake management: The habu Washington, D.C., USA. and the brown treesnake,. Cornell MCKEOWN, S. 1978. Hawaiian reptiles and University Press, Ithaca, New York, amphibians. Oriental Publishing NY, USA. Company, Honolulu, HI, USA. _____, M.J. MCCOID, AND R.L. HADDOCK. MOONEY, H.A., AND R.J. HOBBS, EDITORS. 1994. Symptoms and circumstances 2000. Invasive species in a changing associated with bites by the brown tree world. Island Press, Washington, D.C., snake (: Boiga irregularis) USA. on Guam. Journal of Herpetology MOYLE, P.B. 1973. Effects of introduced 28:27-33. bullfrogs, (Rana catesbeiana), on the KATS, L.B., AND R.P. FERRER. 2003. Alien native frogs of the San Joaquin Valley, predators and amphibian declines: California. Copeia 1:18-22. Review of two decades of science and PITT, W.C., AND R.E. DORATT. 2005. Efficacy the transition to conservation. Diversity of hydrated lime on Eleutherodactylus and Distributions 9:99-110. coqui and an operational field- KRAUS F., AND E.W. CAMPBELL. 2002. application assessment on the effects on Human-mediated escalation of a non-target invertebrate organisms. formerly eradicable problem: The USDA, APHIS, WS, National Wildlife invasion of frogs in the Research Center, Internal report. Hilo, Hawaiian Islands. Biological Invasions HI, USA. 4(4):327-332 _____, AND H. SIN. 2004a. Dermal toxicity of _____, _____, A. ALLISON, AND T. PRATT. citric acid based pesticides to introduced 1999. Eleutherodactylus frog Eleutherodactylus frogs in Hawaii. introductions to Hawaii. Herpetological USDA, APHIS, WS, National Wildlife Review 30:21-25. Research Center. Report to Hawaii LOWE, S., M. BROWNE, S. BOUDJELAS, AND M. Department of Agriculture. Hilo, HI, DE POORTER. 2004. 100 of the world’s USA. worst invasive alien species: A selection _____, AND _____. 2004b. Testing citric acid from the global invasive species use on plants. Landscape Hawaii database. The Invasive Species July/August 5/12. Specialist Group, Species Survival POUGH, F.H., R.M. ANDREWS, J.E. CADLE, M.L. Commission, World Conservation CRUMP, A.H. SAVITZKY, AND K.D. Union. WELLS. 1998. Herpetology. Prentice LUNTZ, S. 1998. Virus can't be used to control Hall, Inc. cane toads. Australasian Science RODDA, G.H., AND T.H. FRITTS. 1992. The 19(8):10. impact of the introduction of the MACK, R. N., D. SIMBERLOFF, W.M. LONSDALE, colubrid snake Boiga irregularis on H. EVANS, M. CLOUT, AND F. BAZZAZ. Guam's lizards. Journal of Herpetology 2000. Biotic invasions: Causes, 26:166-174. epidemiology, global consequences and SAVIDGE, J.A. 1988. Food habits of Boiga control. Ecological Applications irregularis, an introduced predator on 10:689-710. Guam. Journal of Herpetology 22:275- MCCOID, M.J. 1995. Non-native reptiles and 282. amphibians. Pages 433-437 in E.T. SIMBERLOFF, D. 1995. Why do introduced Laroe, G.S. Farris, C.E. Puckett, P.D. species appear to devastate islands more Doran, and M.J. Mac, editors. Our living than mainland areas? Pacific Science resources: A report to the nation on the 49:87-97. distribution, abundance, and health of _____, AND B. VON HOLLE. 1999. Positive U.S. plants, animals, and ecosystems. interactions of nonindigenous species: U.S. Department of the Interior,

118 Invasional meltdown? Biological Symposium. National Wildlife Invasions 1:21-32. Research Center, Ft. Collins, CO, USA. VICE, D.S., AND R.M. ENGEMAN. 2000. Brown _____, AND D.L. VICE. 2004. Characteristics of tree snake discoveries during detector brown treesnakes removed from Guam’s dog inspections following Supertyphoon transportation network. Pacific Paka. Micronesica 33:105-110. Conservation Biology 10:216-221. _____, _____, AND D.L. VICE. 2005a. A _____, _____, AND J.C. GIBBONS. 2005b. Wild comparison of three trap designs for by brown treesnakes capturing brown treesnakes on Guam. (Boiga irregularis) on Guam. Wildlife Research 32:355-359. Micronesica 38:121-124. _____, AND M.E. PITZLER. 1999. Management WILLIAMSON, I. 1999. Competition between of the yellow bittern (Ixobrychus the larvae of the introduced cane toad sinensis) on Guam to minimize threats Bufo marinus (Anura : Bufonidae) and to aviation safety. Proceedings of the native anurans from the Darling Downs North American Birdstrike Committee area of southern Queensland. Australian 1:133-138. Journal of Ecology 24:636-643 _____, AND _____. 2002. Brown treesnake ZUG, G.R. 2004. Systematics of the Carlia control: Economy of scales. Pages 127- ‘fusca’ lizards (: Scincidae) of 131 in L. Clark, editor. Human conflicts and nearby islands. Bishop with wildlife: Economic considerations. Museum Bulletin in Zoology 5:1-83 Proceedings of the Third NWRC Special

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