Photographic validation of target versus nontarget take of brown treesnake baits

Shane R Siers,Stephen M Mosher,Cynthia G Payne,Craig S Clark,Aaron B Shiels,Francine M Chlarson

doi:10.1002/wsb.1023

Shane R Siers, Stephen M Mosher + Show 4 more

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https://doi.org/10.1002/wsb.1023

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Abstract

ABSTRACTUse of toxic baits or other tools for managing nuisance species must ensure that the species of interest is adequately targeted while exposure to nontarget species is minimized. Nontarget takes of acetaminophen‐laced baits for control of invasive brown treesnakes (Boiga irregularis) on Guam may put those animals at risk of lethal intoxication and render the bait unavailable to the intended target species. We used wildlife cameras to identify species removing toxic and nontoxic baits from brown treesnake bait stations designed to exclude nontarget taxa in 2015 and 2016. Throughout various sites and habitat types, and balanced by season (wet vs. dry), we monitored 512 bait stations. From those, 140 of the baits were taken and the species taking the bait was successfully identified. Brown treesnakes took 124 (88.6%) of the baits, 13 (9.3%) were taken by small coconut crabs (Birgus latro), and 3 (2.1%) were taken by monitor lizards (Varanus indicus). The greatest incidence of nontarget bait takes was by small coconut crabs at 2 adjacent sites atop the same cliff line during a single season; 96.9% of bait takes at all other sites were by brown treesnakes. Bait takes by brown treesnakes were particularly infrequent (2.3%) at sites associated with endangered swiftlet (Aerodramus bartschi) caves where intensive snake control was employed. Although the majority of baits in bait stations are taken by brown treesnakes, local and temporal pulses in nontarget species activity, particularly by crabs, may bias results, which would not be accounted for without supplemental validation by cameras. © 2019 The Authors. Wildlife Society Bulletin published by Wiley Periodicals, Inc. on behalf of The Wildlife Society. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.

Highlights

Triggered by nontargets become nonfunctional for trapping the target species, and baits consumed by nontargets are no longer available for ingestion by targets
Current efforts typically rely on 3 methods: traps baited with live mice (Vice et al 2005); spotlighting and hand‐removal along fence lines (Engeman and Vice 2001); and application of toxic baits in bait stations intended to exclude nontarget organisms such as crabs, rats, and monitor lizards (Varanus indicus; Savarie et al 2001, Clark et al 2012, Lardner et al 2013)
Trigger, and Bait Tube System We offered dead newborn mouse baits in 30‐cm lengths of 5.1‐cm‐inner‐diameter polyvinyl chloride (PVC) tube with steel bolts bisecting the openings at each end to limit access by nontarget species, as used for operational snake control by Wildlife Services

Summary

Introduction

Triggered by nontargets become nonfunctional for trapping the target species, and baits consumed by nontargets are no longer available for ingestion by targets. Densities have dropped since the collapse of large prey populations, they are still unusually high, generally estimated at approximately 25/ha (Rodda et al 1999) This invasive predator is currently the subject of a multiagency control program to prevent spread of the species throughout the Pacific Rim (e.g., Shwiff et al 2010, Hawaii Interagency Biosecurity Plan 2017). Current efforts typically rely on 3 methods: traps baited with live mice (Vice et al 2005); spotlighting and hand‐removal along fence lines (Engeman and Vice 2001); and application of toxic baits in bait stations intended to exclude nontarget organisms such as crabs, rats, and monitor lizards (Varanus indicus; Savarie et al 2001, Clark et al 2012, Lardner et al 2013).

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