Brown Treesnake Mortality After Aerial Application of Toxic Baits

Abstract

Quantitative evaluation of control tools for managing invasive species is necessary to assess overall effectiveness and individual variation in treatment susceptibility. Invasive brown treesnakes (Boiga irregularis) on Guam have caused severe ecological and economic effects, pose a risk of accidental introduction to other islands, and are the greatest impediment to the reestablishment of extirpated native fauna. An aerial delivery system for rodent‐based toxic baits can reduce brown treesnake abundance and heterogeneity among individuals may influence bait attraction or toxicant susceptibility. Previous baiting trials have either been simulated aerial treatments or relied on slightly different bait capsule compositions and the results of aerial delivery of toxic baits under operational conditions may not be directly comparable. We monitored 30 radio‐tagged adult snakes (990–1,265 mm snout‐vent length) during an aerial baiting operation in a 55‐ha area using transmitters equipped with accelerometers and receivers programed to display a status code indicating mortality if a snake failed to move for >24 hours. We used known‐fate models to estimate mortality and evaluate a priori hypotheses explaining differences in mortality based on size, sex, and treatment effects. Eleven radio‐tagged snakes died in the aerial baiting treatment period (0.37, 95% CI = 0.21–0.55) and no individuals (0.00, 95% CI = 0.00–0.04) died during the non‐treatment period. Our data provide strong evidence for an additive size‐based treatment effect on mortality, with smaller adults (0.59, 95% CI = 0.35–0.80) exhibiting higher mortality than larger snakes (0.14, 95% CI = 0.02–0.37) but did not support a sex effect on mortality. The high mortality of snakes during the treatment period indicates that aerial baiting can reduce brown treesnake abundance, but further refinement or use in combination with other removal tools may be necessary to overcome size‐based differences in susceptibility and achieve eradication. © 2021 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.

Adaptive resource management: Achieving functional eradication of invasive snakes to benefit avian conservation

“…For example, likely due to the ease of application and the scale at which ADS could be applied, the greatest per control day removal of snakes was by use of this tool. However, snakes in larger size classes have lower susceptibilities to acetaminophen intoxication and a reduced probability of mortality (Goetz et al., 2021; Siers et al., 2021), whereas carrion was apparently less attractive to snakes in good condition. The addition of live avian lures to the control programme was critical for removing good‐condition individuals and achieving extant avian responses.…”

A Review of Common Factors among Successful and Failed Efforts to Eradicate Invasive Vertebrates in Florida

“…Various removal methods targeting Trioceros jacksonii (Boulenger) (Jackson's Chameleon) in Hawaii have also been largely ineffective for similar reasons (Van Kleeck and Holland 2018). In both cases, the use of acetaminophen has been proposed as a potential solution (Goetz et al 2021, Van Kleeck and Holland 2018), which has also been tested as a potential method to remove Nile Monitors and Burmese Python in Florida (Mauldin and Savarie 2010). However, like concerns with other methods, the impacts of acetaminophen to non-target species are a major concern, especially in urban areas such as those inhabited by the Nile Monitor where non-target mortalities of pets could occur.…”

“…Determining a proper removal method is a common obstacle to efforts to eradicate herpetofauna. For example, efforts to control Boiga irregularis (Bechstein) (Brown Tree Snake) in Guam have been limited by the labor demands and lack of large-scale application of most removal methods (Goetz et al 2021). Various removal methods targeting Trioceros jacksonii (Boulenger) (Jackson's Chameleon) in Hawaii have also been largely ineffective for similar reasons (Van Kleeck and Holland 2018).…”

Demographic response of brown treesnakes to extended population suppression

“…Likewise, bait attractiveness or palatability may be affected by size‐dependent attraction to dead neonatal mice, with larger snakes showing less interest (Savidge 1988, Shivik and Clark 1999). Prior studies of ADS‐treated populations suggested an accumulation of the largest snakes and the smallest snakes may occur after treatment and that large snakes may have lower risk of mortality (Nafus et al 2020, Goetz et al 2021), supporting reduced efficacy of small mouse‐based toxicants in removing those demographics. Although large snakes do consume and die from the baits, they may have increased survival rates relative to smaller size classes interested in endothermic prey (Siers et al 2021).…”