Evaluating lethal toxicant doses for the largest individuals of an invasive vertebrate predator with indeterminate growth

Siers, Shane R.; Goetz, Scott M.; Volsteadt, Rachel M.; Nafus, Melia G.

doi:10.3391/mbi.2021.12.2.17

Cited by 10 publications

(9 citation statements)

References 3 publications

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“…Mid-sized BTS may pose the largest risk due to its relative abundance being sustained by high recruitment from the smaller size class (Siers et al, 2017a). Current suppression tools may not be fully effective for very large BTS (Nafus et al, 2020;Goetz et al, 2021;Siers et al, 2021) and may have an effect disproportional to their low abundance (Siers et al, 2017a). With improvements in evaluating BTS contact rates and size distributions (e.g., Siers et al, 2021) our results can help to translate this information into the risk for each bird species under a given level of BTS predation threat.…”

Section: Discussionmentioning

confidence: 99%

Distilling Professional Opinion to Gauge Vulnerability of Guam Avifauna to Brown Treesnake Predation

McElderry¹,

Paxton²,

Nguyen³

et al. 2021

Front. Conserv. Sci.

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The avifauna of Guam was devastated by the introduction of the Brown Treesnake, and the restoration of native birds would need to address the problem with eradication or suppression of BTS. With eradication of the snake unlikely in the near term, and suppression capabilities limited to specific finite areas, key information for reintroductions is how low BTS abundance will likely need to be for each bird species to be re-established based on their vulnerability to BTS predation. Here, we estimate vulnerability, which can no longer be measured directly, so biologists who are familiar with one or more of seven Guam birds were surveyed to obtain their knowledge and produce quantitative vulnerability estimates. As is typical of birds adapted to islands devoid of predators, respondents judged that our focal species exhibit few predator avoidance and tolerance traits, leaving body size as the prime determinant of vulnerability. Respondent opinion also holds that any behavior that reduces the likelihood of an encounter by BTS, e.g., roosting/nesting in palm crowns, cavity nesting, and in particular urban dwelling, substantially reduces vulnerability. Our results can help inform species-specific decisions about when it may be safe to consider the release of birds on Guam depending on the relative vulnerability of each species to predation by BTS.

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Section: Discussionmentioning

confidence: 99%

Distilling Professional Opinion to Gauge Vulnerability of Guam Avifauna to Brown Treesnake Predation

McElderry¹,

Paxton²,

Nguyen³

et al. 2021

Front. Conserv. Sci.

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“…We also considered the possibility that toxicant dosage influenced size‐based mortality because the 80‐mg acetaminophen tablet could have a larger effect on smaller snakes but concluded this explanation is unlikely given that Savarie et al (2001) reported an 80‐mg dose orally delivered in a dead mouse to be 100% lethal for snakes ( n = 29) <300 g in mass. Although there is evidence that some very large snakes will survive a single 80‐mg dose, survival is very rare until masses exceed 250 g (Siers et al 2021), which is larger than any subject in this trial; snakes >250 g account for <7% of males and <2% of females captured during a systematic island‐wide visual sampling effort (Siers 2015, Siers et al 2017 b ). Given the similar diets and lethality of acetaminophen among males and females, we found no sex‐specific effect on probability of mortality.…”

Section: Discussionmentioning

confidence: 89%

“…Dead neonatal mice remain viable baits for brown treesnakes for approximately 48-72 hours post-deployment. Once baits are ingested, snakes may take an additional 24-48 hours (Mathies and Mauldin 2020) or longer for larger snakes (Siers et al 2021) to succumb to the toxin and another 24 hours following death for transmitters to broadcast a mortality signal. In accordance, we determined the effective treatment period to extend 7 days beyond the final application, or the 2-week period between 7 June through 21 June 2019.…”

Section: Analysesmentioning

confidence: 99%

Brown Treesnake Mortality After Aerial Application of Toxic Baits

et al. 2021

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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.

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“…For figures A and B lines depict all known individuals (all), those susceptible to mouse baits (≥850-mm snout-vent length [SVL, mm]), and reproductively sized females (≥1,000 mm SVL) 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). Given these considerations, changes in food availability would also be anticipated to affect eradication timelines.…”

Section: Discussionmentioning

confidence: 99%

Demographic response of brown treesnakes to extended population suppression

et al. 2021

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From a management perspective, reptiles are relatively novel invasive taxa. Few methods for reptile control have been developed and very little is known about their effectiveness for reducing reptile populations, particularly when the goal is eradication. Many reptiles, and especially snakes, are cryptic, secretive, and undergo extended periods of inactivity, traits that decrease detection probabilities and create challenges in estimating population size or evaluating management effects. The brown treesnake (Boiga irregularis) is a notorious invasive species that continues to cause major ecological and economic harm following their introduction to the island of Guam after World War II. They have been the subject of intensive research on the effectiveness of various techniques to control snakes, including the first ever aerial system for the distribution of toxic acetaminophen baits for reptile control. We provide a cohort-based life table for a cryptic and invasive reptile undergoing extended population control using toxic baits from March 2017-2020.We also evaluated the effects of single (toxic bait) versus multitool (toxic bait and live trapping) management efforts on population trajectories, and estimated which population vital rates are most important for influencing population growth or decline in a treated landscape. Treatment of the population with acetaminophen-laced baits resulted in an immediate reduction followed by a gradual population decline that suggested that

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Evaluating lethal toxicant doses for the largest individuals of an invasive vertebrate predator with indeterminate growth

Cited by 10 publications

References 3 publications

Distilling Professional Opinion to Gauge Vulnerability of Guam Avifauna to Brown Treesnake Predation

Distilling Professional Opinion to Gauge Vulnerability of Guam Avifauna to Brown Treesnake Predation

Brown Treesnake Mortality After Aerial Application of Toxic Baits

Demographic response of brown treesnakes to extended population suppression

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