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USDA National Wildlife Research Center Managing Invasive Symposia

8-1-2007

MANAGEMENT OF INVASIVE IN THE UNITED STATES: AN OVERVIEW

Gary W. Witmer USDA-APHIS-Wildlife Services, [email protected]

Patrick W. Burke USDA-APHIS-Wildlife Services

Will C. Pitt USDA-APHIS-Wildlife Services

Michael L. Avery USDA-APHIS-Wildlife Services, [email protected]

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Witmer, Gary W.; Burke, Patrick W.; Pitt, Will C.; and Avery, Michael L., "MANAGEMENT OF INVASIVE VERTEBRATES IN THE UNITED STATES: AN OVERVIEW" (2007). Managing Vertebrate Invasive Species. 56. https://digitalcommons.unl.edu/nwrcinvasive/56

This Article is brought to you for free and open access by the USDA National Wildlife Research Center Symposia at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Managing Vertebrate Invasive Species by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln.

MANAGEMENT OF INVASIVE VERTEBRATES IN THE UNITED STATES: AN OVERVIEW

GARY W. WITMER AND PATRICK W. BURKE , USDA/APHIS/WS National Wildlife Research Center, Fort Collins Colorado, USA WILL C. PITT , USDA/APHIS/WS National Wildlife Research Center, Hilo Hawaii, USA MICHAEL L. AVERY , USDA/APHIS/WS National Wildlife Research Center, Gainesville , USA

Abstract: At least 161 introduced/invasive vertebrates have become established in the United States and its territories, including at least 81 mammalian, 94 avian, and 86 reptilian/ species. Particularly problematic species include feral cats and dogs; feral pigs; commensal rats and mice; starlings, pigeons, and house sparrows; and bullfrogs, brown treesnakes, and coqui . We briefly review these introductions and the types of damage they cause. We review the basic types of methods used for control or eradication of each taxonomic group, including physical, chemical, biological, and cultural methods. We also discuss some of the challenges in managing these species, including issues with the use of toxicants, land access, public attitudes, and monitoring difficulties. Finally, we discuss some ongoing research and future research needs, including fertility control, improved detection methods, improved attractants, improved barriers, improved capture methods, and risk assessment methods.

Key Words: damage, eradication, introduced species, invasive species, management.

Managing Vertebrate Invasive Species: Proceedings of an International Symposium (G. W. Witmer, W. C. Pitt, K. A. Fagerstone, Eds). USDA/APHIS/WS, National Wildlife Research Center, Fort Collins, CO. 2007.

INTRODUCTION Unfortunately, for many species of introduced Vertebrate species have been introduced to vertebrates, we do not yet know if they are causing, almost all parts of the world for thousands of years. or in the future will cause, significant harm to the The large volume of worldwide trade and environment or human resources. Hence, our use transportation have accelerated the rate of of the term “introduced/invasive” vertebrate introductions in the last 150 years or so. spieces. are introduced for many reasons, both purposeful Lists of mammalian (Long 2003) and avian and accidental. Purposeful introductions occur for (Long 1981, Lever 1987) introductions around the food and fur, work animals, sport hunting and world have been compiled with relatively minor fishing, companion animals, aesthetics, and pest discussion of impacts and control efforts. As control. Accidental introductions occur because of political and social awareness has grown, efforts to stowaways in transport vehicles, released animals assess introduced species and their adverse impacts (without an original intent to release), escapees, have increased (Pimentel et al. 2005). A and, in some cases, because of range expansion of a conference held in in 2001 brought species (often facilitated by human activities and attention to the widespread problems with invasive land uses). species and illustrated many of the diverse projects While many introduced vertebrate species have being conducted around the world to try to resolve provided important resources and economic gains some of the situations (Veitch and Clout 2002). for humans and many do not cause undue adverse Witmer and Lewis (2001) reviewed vertebrate effects (especially with appropriate management), introductions in the Pacific Northwestern Region of some have increased their distribution and have the United States (US), the resultant impacts, state caused serious adverse effects. These include and federal legislation, management methods and disease and safety hazards, predation and strategies, and some case studies for , competition with native species, crop consumption mammals, and / (herptiles). At and contamination both in the field and during the 12 th Wildlife Damage Management Conference storage, livestock predation, and, in some cases, in Traverse City, Michigan (2005), speakers significant environmental degradation. reviewed issues of introduced birds (Avery and

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Tillman 2005), herptiles (Pitt et al. 2005), ungulates and established species. It appears that a large (Lowney et al. 2005), carnivores (Witmer et al. portion of the introduced vertebrates occur in 2005), and rodents (Witmer and Eisemann 2005). Florida, Texas, California, and Hawaii; however, Pitt and Witmer (2007) reviewed issues associated all states have a number of well-established with invasive predators across several taxa. introductions. In this paper, we compile and update lists of At least 81 species of introduced/invasive introduced vertebrates (mammals, birds and mammals have become established in parts of the herptiles) in the US (mainland and Hawaii). We US (Table 1). Mammals were mainly introduced present some of the most problematic species and for sport hunting, but also for food and fur (Kraus the types of adverse impacts they cause. We also 2003). The largest single group is ungulates with list the main management methods and tools used 33 species. This group includes many species used to control and eradicate invasive vertebrates in the for sport hunting (e.g., aoudad, gemsbok, nilgai, US. Finally, we discuss some of the remaining eland), but also feral populations of species that challenges in addressing invasive vertebrate were used for work (e.g., horses, burros) or for food management in the US and some research needs. (e.g., cattle, pigs). The second largest group of Scientific names are presented in the tables and are mammals is rodents (18), many of which were not repeated in the text. introduced accidentally via cargo and transport vehicles (commensal rats and mice), but some were VERTEBRATES INTRODUCED IN THE purposefully introduced for fur (e.g., nutria). UNITED STATES Numerous carnivores (14 species) have been We compiled our lists of introduced vertebrate introduced, in some cases for their fur (e.g., foxes, species in the US from a variety of sources, ), but also in efforts to control pests such including several publications (e.g., Bury and as rats and snakes (e.g., mongoose, weasels). There Luckenbach 1976, Long 1981, Mooney and Drake are also large populations of feral, formerly 1986, Moulton and Pimm 1986, Lever 1987, companion animals (e.g., dogs, cats) throughout the Hawaii Audubon Society 1989, American US Interestingly, at least 6 species of primates Ornithologist’s Union 1998, Witmer and Lewis have become established in parts of the US 2001, Long 2003, Teer 2003, Meshaka 2006, Kraus At least 94 species of introduced/invasive birds 2007), but also from several state wildlife agency have become established in the US (Table 2). Most and conservation organization websites (available introductions were as pets, but many were upon request). Our focus was on the US mainland introduced for sport hunting (Kraus 2003). Most of and Hawaii, so we have not included some of the these are passerines (39 species), but many are species introduced to US territories such as the US psitticines (22 species, popular animals in the pet Virgin Islands, Puerto Rico, and Guam. An industry). There are also a large number (20 important exception is the inclusion of the brown species) of “upland ”/galliform birds (both treesnake in Guam as it is a major problem invasive native and non-native) that have been introduced to species receiving a considerable investment in various parts of the US. Interestingly, many more research and control efforts. The list we have avian species have been introduced to Hawaii than compiled is quite long because we have included the mainland (Lever 1987). many species that are native to North America, but At least 86 species of introduced/invasive have been translocated to states or regions in which herptiles have been introduced to the US (Table 3). they did not occur historically. We have also Most introductions were as pets, but many were included some species that have expanded their also introduced as accidentals in cargo (Kraus historic range in recent decades because, in many 2003). This group of animals is also very popular cases, this range expansion has been facilitated, at in the pet industry. Florida is a very large importer least in part, by the activities and land uses of of herptiles which may be why that state seems to humans. The list may actually be considerably have the largest number of established species. The longer, but for many species, we cannot yet be sure largest single group of herptiles is (61 that they are well established and will sustain species). Other groups (frogs and toads, turtles, themselves over time. For example, Florida snakes) comprise smaller (6-9 species) and agencies use a “10 year rule” of documentation of relatively similar numbers of species per group. breeding and establishment in several counties Only one crocodilian (caiman) has become before the species is put on its listed of introduced established in a few parts of the US.

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Table 1. Mammals introduced into parts of the US.

MARSUPIALS: Mexican red-bellied squirrel ( S. UNGULATES: Opossum ( Didelphis marsupialis ) aureogaster ) Donkey (burro)( Equus asinus ) Brush-tailed rock wallaby Gray squirrel ( S. carolin)nsis Feral horse ( E. caballus ) (Petrogale penicillata ) ( S. niger ) Burchell’s zebra ( E. burchelli ) Red squirrel ( S. vulgaris ) ( Sus scrofa ) PRIMATES: Kangaroo rat ( Dipodomys ordii ) Camel ( Camelus bactrianus ) Squirrel monkey ( Saimiri sciureus ) Deer mouse ( Peromyscus Axis deer ( Cervus axis ) Vervet monkey ( cercopithecus maniculatus ) Fallow deer ( C. ) aethiops ) Red-backed vole ( Clethrionomys Swamp deer ( C. duvauceli ) Crab-eating Monkey ( Macaca rutilus ) Wapiti (American , ) ( C. fascicularis ) Muskrat ( Ondatra zibethicus ) elaphus ) Japanese macaque ( M. fuscata ) Polynesian rat (kiore) ( Rattus ( C. Nippon ) Rhesus monkey ( M. mulatto ) exulans ) Sambar deer ( C. unicolor ) Chimpanzee ( Pan troglodytes ) Norway (brown) rat ( R. norvegicus ) Black-tailed deer ( Odocoileus Ship (black, roof) rat ( R. rattus ) hemionus ) INSECTIVORES: Gambian giant pouched rat ( Capreolus capreolus ) Nine-banded armadillo ( Dasypus (Cricetomys gambianus ) ( Alces alces ) novemcinctus ) House mouse ( Mus musculus ) (caribou)(Rangifer Pallas’s mastiff bat ( Molossus Beaver ( Castor canadensis ) tarandus ) molossus ) Nutria ( Myocastor coypus ) antelope ( Antilocapra Americana ) LAGOMORPHS: CARNIVORES: Eland ( Taurotragus oryx ) Eastern cottontail ( Sylvilagus ( Vulpes vulpes ) Nilgai ( Boselaphus tragocamelus ) floridanus ) Arctic fox ( Alopex lagopus ) Water buffalo ( Bubalus bubalis ) European ( Oryctolagus Feral dog ( Canis familiaris ) Feral cattle ( Bos Taurus ) cuniculus ) ( C. latrans ) Bison ( Bison bison ) ( Lepus americanus ) ( Procyon lotor ) Gemsbok ( Oryx gazelle ) Black-tailed jackrabbit ( L. Coatimundi ( Nasua nasua ) Blackbuck ( Antilope cervicapra ) californicus ) White-nosed coati ( N. narica ) ( Oreamnos ( L. europaeus ) Stoat (ermine, short-tailed weasel) americanus ) White-tailed jackrabbit ( L. (Mustela erminea ) Chamois ( Rupicapra rupicapra ) townsendii ) Least weasel ( M. nivalis ) Musk-ox ( Ovibos moshatus ) ( M. putorius ) Himalayan tahr ( Hemitragus RODENTS: American mink ( M. vision) jemlahicus ) Arctic ground squirrel Small Indian mongoose ( Herpestes Feral goat ( Capra hircus ) (Spermophilus parryii ) auropunctatus ) Alpine ibex ( C. ibex ) Prairie dog ( Cynomys ludovicianus ) Feral cat ( Felis catus ) Aoudad (Barbary sheep) Abert’s squirrel ( Sciurus aberti ) Jaguarundi ( F. yagouaroundi ) (Ammotragus lervia ) Mouflon sheep ( Ovis ammon ) Feral sheep ( O. aries ) ( O. canadensis )

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Table 2. Birds introduced into parts of the US.

ANSERIFORMES: Eurasian collared dove ( S. decaocto ) Northern mockingbird ( Mimus ( Cygnus olor ) Spotted dove ( S. chinensis ) polyglottos ) Mandarin duck ( Aix galericulata ) Barred (zebra) dove ( Geopelia striata ) White-rumped shama ( Copsychus Muscovy duck ( Cairina moschata ) White-winged dove ( Zenaida asiatica ) malabaricus ) ( Anas rubripes ) ( Z. macroura ) Melodious laughing thrush ( Garrulax ( A. platyrhynchos ) canorus ) PSITTACIFORMES: Greater necklaced laughing thrush ( G. CICONIIFORMES: Monk parakeet ( Myiopsitta monachus ) pectoralis ) Cattle egret ( Bubulcus ibis ) Ring-necked (rose-winged) parakeet Red-billed leiothrix ( Leiothrix lutea ) (Psittacula krameri ) Japanese bush warbler ( Cettia : Canary-winged (white-winged) diphone ) Plain chachalaca ( Ortalis vetula) parakeet ( Brotogeris versicolurus ) Varied tit (Parus varius ) Bobwhite quail ( Colinus virginianus ) Blue-crowned parakeet ( Aratinga Japanese white-eye ( Zosterops Mountain quail ( Oreortyx picta ) acuticaudata ) japonica ) California quail ( Lophortyx Budgerigar ( Melopsittacus undulatus ) Saffron finch ( Sicalis flaveola ) californicus ) Green-cheeked Amazon (red-crowned Yellow-faced grassquit ( Tiaris Gambel’s quail ( L. gambellii ) parrot) ( Amazona viridigenalis ) olivacea ) Scaled quail ( Callipepla ) Yellow-crowned Amazon ( A. Red-crested cardinal ( Paroaria Chukar ( Alectoris chukar ) ochrocephula ) coronata ) Barbary partridge ( A. Barbara ) Yellow-headed Amazon ( A. oratrix ) Yellow-billed cardinal ( P. capitata ) Grey partridge ( perdix ) Blue-fronted Amazon ( A. aestiva ) Common (northern ) cardinal Black francolin ( Francolinus Lilac-crowned parrot (Cardinalis cardinalis) francolinus ) Senegal parrot ( Poicephalus Spot-breasted oriole ( Icterus ( F. pondicerianus ) senegalus ) pectoralis ) Erkel’s francolin ( F. erkelii ) Blue-fronted conure ( Aratinga Yellow-fronted canary ( Serinus Himalayan snowcock ( Tetragallus cruentata ) mozambicus ) himalayensis ) Brown-throated conure ( A. pertinax) Common canary ( S. canaria ) (coturnix Mitered conure ( A. mitrata) House finch ( Carpodacus mexicanus ) quail)( Coturnix coturnix ) Nanday conure (black-hooded Red-cheeked condon-bleu Chinese bamboo partridge parakeet) ( Nandayus nenday ) (Uraeginthus benglaus ) (Bambusicola thoracica ) Lovebird ( Agapornis spp.) Lavender waxbill ( Estrilda Kalij pheasant ( Lophura leucomelana ) Cockatiel ( Nymphicus hollandicus ) caerulescens ) Red jungle fowl ( Gallus gallus ) Sulphur-crested cockatoo ( Cacatua Orange-cheeked waxbill ( E. melpoda ) Common (ring-necked) pheasant galerita ) Common waxbill ( E. astrild ) (Phasianus colchicus ) White-crested cockatoo ( C. alba ) Black-rumped waxbill ( E. troglodytes ) Reeve’s pheasant ( Syrmaticus Giffin’s cockatoo ( Cacatua goffini ) Red avadavat ( Amandava amandava ) reevesii ) Nutneg manikin ( Lonchura Helmeted guineafowl ( Numida STRIGIFORMES: punctulata ) meleagris ) Barn owl (Tyto alba ) Black-headed manikin ( L.malacca ) Common peafowl ( Pavo cristatus ) Warbling silverbill ( L. malabarica ) White-tailed ptarmigan ( Lagopus PASSERIFORMES: Orange bishop ( Euplectes leucurus ) Edible-nest swiftlet ( Aerodramus franciscanus ) Common ( Melagris gallopavo ) fuciphagus ) Java sparrow ( Padda oryzivora ) Chesnut-bellied sandgrouse ( Pterocles Mariana swiftlet ( A. bartschi ) House sparrow ( Passer domesticus ) exustus ) Skylark ( Alauda arvensis ) European tree sparrow ( P. montanus ) ( Bonasa umbellus ) Western meadowlark ( Sturnella European starling ( Sturnus vulgaris ) neglecta ) Common mynah ( Acridotheres tristis ) COLUMBIFORMES: Red-vented bulbul ( Pycnonotus caferi ) Hill mynah ( Gracula religiosa ) Feral pigeon (rock dove) ( Columba Red-whiskered bulbul ( P. jocosus ) Crested mynah ( Acridotheres livia ) cristatellus ) African collared dove ( Streptopelia roseogrisea )

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Table 3. Reptiles and amphibians introduced into parts of the US.

FROGS AND TOADS: Bark anole ( A. distichus ) Moorish ( Tarentola Giant toad (cane toad)( Bufo Hispaniolan green anole ( A. mauritanica ) marinus ) chlorocyanus ) Ringed wall gecko ( T. annularis ) Green-and-black poison dart Puerto Rican crested anole ( A. Mourning gecko ( Lepidodactylus (Dendrobates auratus ) cristatellus ) lugubris ) Greenhouse frog ( Eleutherodactylus Knight anole ( A. equestris ) Multilating gecko ( Gehyra mutilata ) planirostris ) Cuban green anole ( A. porcatus ) Rough-tailed gecko ( Cyrtopodion Coqui frog ( E. coqui ) Jamaican giant anole ( A. garmani ) scabrum ) Cuban treefrog ( Osteopilus Marie Gallant Sail-tailed anole ( A. Tokay gecko ( Gekko gecko ) septentrionalis ) ferreus ) Common house gecko Rio Grande leopard frog ( Rana Brown anole ( A. sagrei ) (Hemidactylus frenatus ) berlandieri ) Brown basilisk ( Basiliscus vittatus ) Tropical house gecko (wood stave) Green frog ( R. clamitans ) Veiled chameleon ( Chamaeleo (H. mabouia ) American bullfrog ( R. catesbeiana ) calyptratus ) Asian flat-tailed gecko ( H. Japanese wrinkled frog ( Jackson’s chameleon ( C. jacksonii ) platyurus ) rugosa ) Butterfly ( Leiolepis belliana ) Indo-Pacific gecko ( H. garnotti ) African clawed frog ( Xenopus Oriental garden lizard (variable Mediterranean gecko ( H. turcicus ) laevis ) bloodsucker) ( Calotes versicolor ) Yellow-headed gecko ( Gonatodes lizard albogularis ) SALAMANDERS: ( lemniscatus ) Indo-Pacific tree gecko Tiger salamander ( Ambystoma Giant whiptail lizard ( C. (Hemiphyllodactylus typus ) tigrinum ) [Aspidoselis] motaguae ) Moth skink ( Lipinia noctua ) New whiptail lizard ( C. Azure-tailed skink ( Emoia impar ) TURTLES: neomexicanus ) Copper-tailed skink ( E. cyanura ) Red-eared slider ( Trachemys scripta Plateau striped whiptail ( C. velox ) Many-lined grass skink ( Mabuya elegans ) Northern curlytail lizard multifasciata) Painted turtle ( Chrysemys picta ) (Leiocephalus carinatus ) Pacific snake-eyed skink Spiny softshell ( Trionyx spiniferus ) Red-sided curlytail lizard ( L. (Cryptoblepharus poecilopleurus ) Wattle-necked softshell ( Palea schreibersii ) Plague skink ( Lampropholis steindachneri ) Common wall lizard ( Podarcis delicate ) Chinese softshell ( Pelodiscus muralis ) Western green lacerta ( Lacerta sinensis ) Italian wall lizard ( P. sicula ) bilineata ) Snapping turtle ( Chelydra Texas horned lizard ( Phrynosoma Nile monitor ( Varanus niloticus ) serpentine ) cornutum ) Argentina giant tegu ( Tupinambis Black (Gray’s) spinytail iguana merianae ) CROCODILIANS: (Ctenosaura similis ) Spectacled (common) caiman Mexican spinytail iguana ( C. SNAKES: (Caiman crocodilus ) pectinata ) Common boa ( Boa constrictor ) Green iguana ( Iguana iguana ) Burmese python ( Python molurus ) LIZARDS: Ashy gecko ( Brahminy blind snake Red-headed agama ( Agama agama ) elegans ) (Ramphotyphlops braminus ) Giant ameiva ( Ameiva ameiva ) Ocellated gecko ( S. argus ) Javan filesnake ( Acrochordus Large-headed anole ( Anolis cybotes ) Gold dust day gecko ( Phelsuma javanicus ) Green anole ( A. carolinensis ) laticauda ) Diamondback water snake ( Nerodia Giant day gecko ( P. rhombifer ) madagascariensis ) Brown treesnake ( Boiga irregularis ) Orange-spotted day gecko ( P. guimbeaui )

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Although we do not address introduced/invasive all states and territories of the US. These rodents fish in detail in this paper, it is important to cause disease and sanitation problems, consumption acknowledge the substantial size of this group: at and contamination of foodstuffs (both in the field least 150 introduced species (Fuller et al. 1999, and in storage), and property damage (Witmer et al. Fuller 2003). While some of these were accidental 1995, Pimentel et al. 2005, Pitt and Witmer 2007). introductions (e.g., from ballast water), most were They have also caused the extinction or for sport fishing (e.g., trout [ Oncorhynchus spp., endangerment of many endemic species on islands Salmo spp., Salvelinus spp.], bass [ Micropterus (Witmer and Eisemann 2005). spp.]), but many were pet or bait fish releases Starlings, pigeons, and house sparrows are (Fuller 2003). A few were introduced as a food found almost worldwide and throughout almost all source (e.g., tilapia [ Tilapia spp.]) and a few of the US. They are so well established in the US species (e.g., grass carp [ Ctenopharyngodon as to be considered “naturalized” and many people idella ], mosquito fish [ Gambusia affinis ]) were no longer even consider them invasive species. widely introduced to control aquatic vegetation or Nonetheless, they cause sanitation and disease mosquito larvae. More details on fish introductions problems, compete with native birds, and consume can be found in the reviews by Fuller (2003), Fuller and contaminate livestock feed (Witmer and Lewis et al. (1999), Pimentel et al. (2005), and Pitt and 2001, Pimentel et al. 2005). Other serious invasive Witmer (2007). problems are more localized, such as mute swans in several northeastern states. They pose EXAMPLES OF PROBLEMATIC human safety concerns because of their aggressive INTRODUCED VERTEBRATES IN THE behavior and they compete with native bird species UNITED STATES (Avery and Tillman 2005). Populations of monk A number of species within each major parakeets have become established in several states taxonomic group of vertebrates pose serious where they cause power outages by nesting in problems over portions of the US. We give a few transformers (Avery and Tillman 2005). They also examples in each group, based on one or more of pose a significant threat of crop damage if these criteria: their widespread nature and populations become sizable in agricultural areas. population sizes, the seriousness of the problems Finally, ring-necked pheasants were introduced to they cause, the amount of investment in prevention many states for sport hunting. They cause serious and control, and the number of requests of crop damage in some localized situations and may USDA/APHIS Wildlife Services (WS) to deal with compete for resources with native upland bird specific damage situations. WS involvement in species (Witmer and Lewis 2001). invasive vertebrate damage situations was compiled Perhaps the most widespread invasive herptile and discussed by Bergman et al. (2002) and Rennie in the US is the bullfrog. While native to the et al. (2004). eastern US, bullfrogs have been introduced to many Feral cats are found throughout the US and western states. They prey on many aquatic animal cause significant predation of native birds and other species across all taxa, compete for resources, and native animals (Pimentel et al 2005, Witmer et al. have contributed to the threatened or endangered 2005, Pitt and Witmer 2007). Feral dogs can be status of many regionally-endemic species of frogs found in most of the states and territories of the US. (Witmer and Lewis 2001, Pitt et al. 2005, Pitt and They pose human safety issues, prey on livestock, Witmer 2007). Other invasive herptile problems in and hybridize with some species of native canids the US are much more localized. In Guam, the (Pimentel et al. 2005, Witmer et al 2005). Feral brown treesnake predates upon, and competes with, pigs are found in at least half of the states in the native species of vertebrates and has caused the US. They cause serious environmental extinction of several of those species. They also degradation, prey on native species, damage crops, regularly cause power outages and pose a safety and pose a disease hazard to livestock and wildlife hazard to people, especially children (Pimentel et (Witmer et al. 2003, Pimentel et al. 2005, Pitt and al. 2005, Pitt et al. 2005, Pitt and Witmer 2007). Witmer 2007). Several species of herbivores Coqui frogs have become well established in (exotic and feral and introduced nutria) also Hawaii where their calling all night disturbs cause ecosystem and crop damage (Witmer and peoples’ rest and has caused a decline in property Lewis 2001). One or more species of commensal values (Pitt et al. 2005, Pitt and Witmer 2007). rats and mice occur everywhere worldwide and in Several large, aggressive, carnivorous species of herptiles (in particular, Burmese pythons and Nile 132 monitor lizards) have become established in parts A wide array of methods is used for carnivore of Florida. They pose human and companion management and eradication (Nogales et al. 2003, animal safety hazards, as well as issues of Witmer et al. 2005). Carnivores are captured with competition and predation with native vertebrate live-traps, leg-hold traps, and snares. For smaller species (Pitt and Witmer 2007). species, kill traps (e.g., conibear traps) are also used. Shooting (day, night, with calling) is often MANAGEMENT AND ERADICATION OF used. Occasionally, aerial shooting is used. INTRODUCED/INVASIVE Exclusion is sometimes used, especially to protect VERTEBRATES small colonies of endangered species. Toxicants A wide array of methods is used to manage are used on a limited basis: toxic baits and the M- invasive vertebrates in the US and these vary 44 cyanide device are sometimes used, especially somewhat by taxonomic group (Table 4). Details on islands (Nogales et al. 2003, Witmer et al. on most of these methods, how they are used, and 2005). A number of methods are not effective with their advantages and disadvantages were presented carnivores and rodents (frightening devices, by Conover (2002), Hygnstrom et al. (1994), and repellents, taste aversion), although research VerCauteren et al. (2005). Eradication strategies continues on these and other methods. Few are more complex and are discussed by taxonomic carnivore eradications have been attempted in the group. US. However, introduced foxes have been Management of invasive rodents most often eradicated from several Aleutian Islands with the utilizes rodenticides, and primarily anticoagulants use of shooting, traps, and toxic baits (Ebbert (Howald et al. 2007). Traps (kill traps, live traps, 2000). glue boards) are used in some situations, but to a A wide array of methods is used for ungulate much lesser extent. These methods are management and eradication (Butchko et al. 2003, supplemented in and around buildings, with Campbell and Donlan 2005, Lowney et al. 2005). practices of exclusion, sanitation, and habitat These include shooting (day, night, over bait, modification (Timm 1994). Day and night shooting aerial), trapping (individual cage traps, snares, is used with some larger species (e.g., nutria; group/corral cage traps), pursuit with dogs, LeBlanc 1994). Most island eradications have exclusion, food removal, and Judas animals. utilized anticoagulant rodenticides---hand Eradications have occurred on a few small islands broadcast, in bait stations, or aerially broadcast and on some sizable, fenced/contained areas of the (Howald et al. 2007). mainland (Butchko et al. 2003, Campbell and Donlan 2005, Lowney et al. 2005). Generally, several methods have been employed to assure success.

Table 4. Methods a used to manage and eradicate invasive vertebrate species in the US.

Method: Trap Shoot Toxi- Dogs Judas Introduced Habitat Barriers Other cants animals predator Manip. methods Group: Rodents X N/O X N/O X X X B Ungulates X X X X X X F Carnivores X X X X X X B, C, T Birds X X X X X X F, D Herptiles X X X X aN/O = nutria only, B = bounty, F = frightening devices, C = compensation, T = trap/neuter/release, D = /nest destruction

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Methods used to manage invasive bird vertebrates with the main exceptions of brown populations are similar to those used for mammals: treesnakes in Guam and feral pigs (in many states). traps (with or without live bird decoys), shooting, Public perception and lack of support have exclusion, and limited use of toxicants (DRC 1339; affected efforts to manage or eradicate vertebrate Witmer and Lewis 2001, Millet et al. 2004, Avery species in the US, as elsewhere in the world and Tillman 2005, Pitt and Witmer 2007). The (National Invasive Species Council 2001). exceptions are that egg and nest destruction is Knowledge levels regarding invasive species and sometimes used with birds and frightening devices the harm they can cause are relatively low amongst are often used to protect relatively small areas. the general public (National Invasive Species While few, if any, bird eradications have been Council 2001, Conover 2002). Furthermore, the conducted in the US, Millett et al. (2004) used public does not readily distinguish between native shooting and toxicants to eradicate invasive and non-native species: as long as an animal looks common mynahs from several small islands in the nice and is not threatening people or causing undue Seychelles. They noted that larger islands were harm, the public tends to view species equally much more difficult, if not impossible, to eradicate, (Wittenberg and Cock 2001). Once it has been and that re-invasion was often a problem on all but established that a species will not cause undo the most remote islands. environmental or human resource harm, it can be Our tool box for management and eradication of placed on a “white” list (Fowler et al. 2007). By invasive vertebrates is perhaps weakest for and large, in the US, species importations are amphibians and reptiles (Witmer and Lewis 2001, viewed as “innocent until proven guilty” (“gray” Pitt and Witmer 2007). Most methods development list) and what is needed is the development of a has occurred for brown treesnakes in Guam and much more inclusive prohibited species “black” list coqui frogs in Hawaii (Pimentel et al. 2005, Pitt et (Witmer and Lewis 2001, Fowler et al. 2007, Pitt al. 2005, Pitt and Witmer 2007). Trapping, hand- and Witmer 2007). The ultimate solution to an capture or pit fall traps are perhaps most commonly invasive species is the eradication of all individuals used with herptiles. Drift fences are often used to in a given area; however, much of the public has a increase effectiveness by directing animals to traps strong dislike for the killing of animals (Conover or pit falls. Night search-and-capture with 2002). Certain species such as feral cats, feral spotlights can be used, and with brown treesnakes, dogs, wild horses, and primates are particularly night fence searches are conducted. Detector dogs sensitive species to address. Furthermore, much of are used to inspect cargo for brown treesnakes and the public has a strong fear and distrust of to help locate Burmese pythons in Florida’s chemicals, and in particular, toxicants. Hence, the Everglades National Park. Toxicants have been management of invasive vertebrates, like all developed and registered for brown treesnakes wildlife, is being conducted in an increasingly (acetaminophen) and for coqui frogs (citric acid complex arena (Conover 2002, Fall and Jackson and hydrated lime solutions; Pitt et al. 2005, Pitt 2002). and Witmer 2007). We are not aware of any The pet industry is a well organized, large, and eradications of introduced herptiles in the US. influential industry in the US (Ginsburg 2004). Exotic pets are very popular with a sizable portion MAJOR ISSUES IN DEALING WITH of the public. And yet, the pet industry is a major INVASIVE VERTEBRATES IN THE pathway for the introduction of vertebrates into the UNITED STATES US (Kraus 2003). Very few vertebrate species are While some progress has been, and is being, prohibited from entry into the US with a prevailing made with invasive vertebrates in the US, there are attitude of “innocent until proven guilty” (Witmer still many challenges and issues to resolve and Lewis 2001, Pitt and Witmer 2007). Greater (National Invasive Species Council 2001, Pimentel cooperation, enforcement, and regulation of the pet et al. 2005). The major emphasis, in terms of industry is needed. attention and funding, for invasive species in the Access to all relevant land and properties is US has been focused on plants, , and essential for the successful management and pathogens (Pimentel et al. 2005). Relatively little eradication of invasive vertebrates. However, effort and few resources have been directed to mangers often face the situation where the work is needed across a wide array of jurisdictions and ownerships. Getting permission to access all these

134 areas rarely occurs and can prevent the success needed to determine on which species we should of even a well-planned, well-funded focus our efforts and resources (Hayes 2003). eradication effort. Furthermore, land management mandates and regulations of CONCLUSION federal and state agencies vary considerably. At least 161 species of introduced/invasive This affects the type of management activities vertebrates occur in the US. We suspect that (burning, chemical use), type of vehicles, and invasive vertebrate species will continue to tools (leg-hold traps, firearms, toxicants) that challenge land and resource managers, ecologists, can be used on certain properties. Some laws and biologists for a long time to come. We also actually protect invasive vertebrate species, suspect that the list of invasive vertebrate species such as the Wild Horse and Burro Act and the in the US will continue to grow; but, hopefully, Migratory Bird Treaty Act. The latter was some species will also be removed from the list. recently amended to exclude some non-native We have had some good successes with invasive bird species in the US such as the mute swan. species management and eradications, especially Finally, there is an overall lack of on islands, but also on some areas of the mainland. coordination and cooperation across As a result of this, along with our collaborations jurisdictions and agencies of all levels of with international colleagues and a growing government in the US. One of the goals of the interest and involvement by the public and National Invasive Species Management Plan agencies, we are becoming more knowledgeable (National Invasive Species Council 2001) is to and pro-active in responding to invasive vertebrate rectify that situation. Eradicating an invasive species. We still have a long way to go in terms of vertebrate species is rarely an easy national organization and cooperation on these undertaking. Very careful planning is needed, issues, resolving various logistical and financial along with adequate resources, public and issues, and improving methods and strategies for agency buy-in, highly trained and motivated many more species. personnel, contingency plans, and a sustained effort (Broome 2005). Each situation is LITERATURE CITED unique in one or more ways; hence, a cook- AMERICAN ORNITHOLOGIST ’S UNION . 1998. Check- book approach cannot be used (Broome 2005). list of North American birds. American With the possible exception of rodents and Ornithologists’ Union, Washington, D.C., USA. ungulates, the methods and strategies used for AVERY , M. AND E. TILLMAN . 2005. Alien birds in management, and especially eradication, of North America—challenges for wildlife managers. invasive vertebrates need improvement Proceedings of the Wildlife Damage Management (Wittenberg and Cock 2001). Much research Conference 11:82-89. BERGMAN , D., M. CHANDLER , AND A. LOCKLEAR . needs to be conducted to improve detection 2002. The economic impact of invasive species to methods. Attractants are needed to attract wildlife services’ cooperators. Pages 169-178 in L. individuals to traps, bait stations, and Clark, editor. Human conflicts with wildlife: detection stations. Method improvements are economic considerations. USDA National Wildlife needed to ensure effective and safe delivery of Reseaerch Center, Fort Collins, Colorado, USA. toxicants, vaccines, and fertility control BROOME , K. 2005. Rat eradication—how to get it right agents. Trained, rapid response teams are without a recipe. Proceedings of the Australasian needed for many more invasive species. Vertebrate Pest Conference 13:152-157. Accessible databases on potential invasive BURY , R., AND R. LUCHENBACH . 1976. Introduced species are needed to summarize species amphibians and reptiles in California. Biological Conservation 10:1-14. identification, biology, ecology, and effective BUTCHKO , P., A. DUFFINEY , AND A. MONTONEY . 2003. detection and management methods. The Eradication of a bovine tuberculosis-postive databases should also identify expertise and captive cervid herd in northeast Michigan. literature that can be consulted. Although a Proceedings of the Wildlife Damage Management variety of databases and websites exist (Sellers Conference 10:408-413. et al. 2005), it would be very useful if these CAMPBELL , K., AND J. DONLAN . 2005. Feral goat could be centralized and standardized (Sellers eradication on islands. Conservation Biology et al. 2004). Finally, risk assessments are 19:1362-1374.

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