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A field test of attractant traps for invasive Burmese pythons (Python molurus bivittatus) in southern Florida

Introduction

Abstract
>Introduction
Methods
Results
Discussion
Acknowledgments
Literature Cited
Figures and Tables

Invasive species are responsible for a wide range of economic and environmental impacts (Pimentel et al. 2005; 2007), and effective control tools for invasive species are therefore desirable. While effective control tools are available or under development for some invasive taxa (Veitch and Clout 2002; Witmer et al. 2008), research to validate the efficacy of control tools has been focused on relatively few species. The majority of research has focused on mammals, plants, and insects, but there has been little research on reptiles (Kraus 2009). Although a wide range of tools and techniques are available to detect and/or capture reptiles (Fitch 1987; Simmons 2002), few of these methods have been subjected to rigorous testing to assess inter- or intraspecific biases in detection probability or degree of population control (Dorcas and Willson 2009). Control methods for brown treesnakes (Boiga irregularis) on Guam are a notable exception, as both visual searches and traps used on Guam have been subjected to rigorous validation (Rodda et al. 1999a; Rodda et al. 2007; Tyrrell et al. 2009; Christy et al. 2010).

In recent years, Burmese pythons (Python molurus bivittatus Kuhl 1820), native to Southeast Asia, have established over thousands of square kilometers of south Florida, USA (Snow et al. 2007a; Harvey et al. 2008), including virtually all of Everglades National Park and Big Cypress National Preserve. While no reliable estimates of population size are available for pythons in southern Florida, over 1500 individual pythons have been collected since 2000 (National Park Service 2010) and individual detection probabilities are likely <1% (Reed and Rodda 2009), implying a large overall population size. Burmese pythons are generalist predators that in Florida prey on a variety of native and introduced terrestrial vertebrates, including threatened species (Greene et al. 2007; Snow et al. 2007b). Ecological impacts of pythons are likely to accrue primarily to species that are already imperiled (Reed and Rodda 2009), although anecdotal evidence suggests that pythons have also caused declines of formerly-common species such as marsh rabbits (Sylvilagus palustris) and raccoon (Procyon lotor; Snow, Mazzotti, pers. obs).

Traps equipped with funnel-style entrances have been used for over a half century to capture a variety of snakes (Jackley 1943; Dargen and Stickel 1949; Fitch 1951), but only a handful of rigorous tests of alternative trap designs have been conducted to assess trap efficacy in demographic terms (e.g., Kihara et al. 1978; Hayashi et al. 1985; Rodda et al. 1999b; Maritz et al. 2007; Tyrrell et al. 2009). With few exceptions (e.g., Keck 1994; Willson et al. 2008), most such tests of snake traps have been associated with control of a few species of invasive snakes, especially the brown treesnake (Boiga irregularis) on Guam and the Habu (Protobothrops flavoviridis) in the Ryukyu Islands of Japan.

There is little published information on successful trap designs for giant constrictors such as pythons. Using six large box traps equipped with bamboo/rattan funnel entrances and baited with live chickens, Auliya (2006) captured 17 reticulated pythons (Broghammerus reticulatus) on Borneo over six months using traps spread across a 4.4 km2 area. A few invasive P. molurus have been captured in traps in Florida (F. Mazzotti, R. Rozar, unpubl. data), but trapping efforts thus far have been geographically diffuse, in areas with apparently low python density, and/or of relatively low intensity in terms of trap-nights. The study presented in this paper represents the first published report of an intensive trapping effort for any species of introduced giant constrictor snake.

Available control tools are unlikely to result in eradication of introduced Burmese pythons or other giant constrictors once a population is well-established and distributed across a large area (Reed and Rodda 2009). Local eradication and/or population suppression at larger geographic scales may be feasible, but control tool development for giant constrictors is clearly in its infancy. Herein, we report a field experiment to evaluate traps for invasive Burmese pythons in the greater Everglades ecosystem. Our goals were to: (a) evaluate relative efficacy of standardised visual searching and trapping using attractant traps; (b) evaluate relative capture rates of two different trap entrance designs; and (c) estimate the total number of pythons present in the trapping area to assess the prospects for population control.

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