Habitat type and structure affect trap capture success of an invasive snake across variable densities

Nafus, Melia G.; Adams, Amy A. Yackel; Klug, Page E.; Rodda, Gordon H.

doi:10.1002/ecs2.2339

Cited by 7 publications

(5 citation statements)

References 42 publications

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“…From a broader perspective, our study contributes to highlight the advantages of gaining information on spatial behavior in the management of invasive species. Spatial ecology studies have enabled managers to understand invasive species' home range, activity patterns and habitat use 11 , 65 , can be also useful to plan when and where to place traps 94 and conduct visual surveys 10 , determine sources of detection bias 15 , identify areas at risk 95 or manage local habitats to prevent spread of invasive species 96 . Therefore, we argue that efforts should be made to turn spatial behavior information into an essential tool for optimizing invasive species management.…”

Section: Discussionmentioning

confidence: 99%

Spatial ecology to strengthen invasive snake management on islands

Maestresalas

Piquet

López-Darias

2023

Sci Rep

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Knowledge on the spatial ecology of invasive predators positively contributes to optimizing their management, especially when involving cryptic and secretive species, such as snakes. However, this information is lacking for most invasive snakes, particularly on islands, where they are known to cause severe ecological and socio-economic impacts. This research is focused on assessing the spatial ecology of the California kingsnake (Lampropeltis californiae) on Gran Canaria to strengthen management actions. We monitored 15 radio-tagged individuals once per day on 9–11 days per month from July 2020 to June 2021 to calculate the species' home range and describe annual activity patterns in the invaded range. To account for the species' diel activity during the emergence period, we additionally monitored snakes from January to May 2021 during three consecutive days per month in four different time intervals each day. We detected movement (consecutive detections at least 6 m apart) in 31.68% of the 1146 detections during the whole monitoring period. Movements most frequently detected were shorter than 100 m (82.24%), and among them the range 0–20 m was the most recurrent (27.03%). The mean distance of movement was 62.57 ± 62.62 m in 1–2 days. Average home range was 4.27 ± 5.35 ha—calculated with the Autocorrelated Kernel Density Estimator (AKDE) at 95%—and did not significantly vary with SVL nor sex. We detected an extremely low value of motion variance (0.76 ± 2.62 σ2m) compared to other studies, with a general inactivity period from November to February, January being the less active month of the year. Diel activity was higher during central and evening hours than during early morning and night. Our results should be useful to improve control programs for this invasive snake (e.g., trap placement and visual survey guidance) on Gran Canaria. Our research highlights the importance of gathering spatial information on invasive snakes to enhance control actions, which can contribute to the management of secretive invasive snakes worldwide.

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Section: Discussionmentioning

confidence: 99%

Spatial ecology to strengthen invasive snake management on islands

Maestresalas

Piquet

López-Darias

2023

Sci Rep

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“…It is also possible that snakes were drawn in gradually at a constant rate (either from the scent or random movements in the landscape), without any increase in the grid's attraction rate, and that bird-attracted snakes (not removed by mouse-traps in Phase III) simply became increasingly common as they decided to move no further but to stay near birds. Alternatively, the study progressed in time through the wet season and trapping during the wet season has been shown to result in higher CPUE (Nafus et al 2018).…”

Section: Discussionmentioning

confidence: 99%

“…Snake control efforts were implemented in 2013 through use of mouse-lure snake traps (15,447 trap nights that removed 392 snakes) to suppress brown treesnakes within the barrier at the GNWR. Based on that control effort, GNWR was considered a snakesuppressed area (Nafus et al 2018) and was used to measure contact rates between birds and brown treesnakes. Snake density within the barrier was unknown at the time of the 2013 removal effort, but 23 snakes per hectare has been documented in a nearby enclosed forested habitat (Christy et al 2010).…”

Section: Study Sitementioning

confidence: 99%

Contact rates with nesting birds before and after invasive snake removal: estimating the effects of trap-based control

Adams¹,

Nafus²,

Klug³

et al. 2019

Self Cite

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Invasive predators are responsible for almost 60% of all vertebrate extinctions worldwide with the most vulnerable faunas occurring on islands. The brown treesnake (Boigairregularis) is a notorious invasive predator that caused the extirpation or extinction of most native forest birds on Guam. The success of avian reintroduction efforts on Guam will depend on whether snake-control techniques sufficiently reduce contact rates between brown treesnakes and reintroduced birds. Mouse-lure traps can successfully reduce brown treesnake populations at local scales. Over a 22-week period both with and without active snake removal, we evaluated snake-trap contact rates for mouse- and bird-lure traps. Bird-lure traps served as a proxy for reintroduced nesting birds. Overall, mouse-lure traps caught more snakes per trap night than did bird-lure traps. However, cameras revealed that bird-lure traps had a snake contact rate almost 15 times greater than the number of successfully captured snakes. Snakes that entered bird-lure traps tended to be larger and in better body condition and were mostly captured in bird-lure traps, despite numerous adjacent mouse-lure traps. Traps placed along grid edges caught more snakes than interior traps, suggesting continuous immigration into the trapping grid within which bird-lure traps were located. Contact between snakes and bird-lure traps was equivalent before and after snake removal, suggesting mouse-lure traps did not adequately reduce the density of snakes that posed a risk to birds, at least at the timescale of this project. This study provides evidence that some snakes exhibit prey selectivity for live birds over live mouse lures. Reliance on a single control tool and lure may be inadequate for support of avian reintroductions and could lead to unintended harvest-driven trait changes of this invasive predator.

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“…1,2A). This area, known as the closed population (CP), was constructed in 2004 with the goal of creating a population of presumed abundance and thoroughly-studied demography of brown treesnakes in the field to assess the efficacy of monitoring and control tools in addition to tracking changes over time and in response to management actions (e.g., Tyrrell et al [2009], Christy et al [2010], Lardner et al [2013], Nafus et al [2018], Siers et al [2018]). The CP was surrounded by a two-way barrier fence (Fig.…”

Section: Field Samplingmentioning

confidence: 99%

Evaluation of camera trap‐based abundance estimators for unmarked populations

Amburgey

Adams

Gardner

et al. 2021

Ecological Applications

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Estimates of species abundance are critical to understand population processes and to assess and select management actions. However, capturing and marking individuals for abundance estimation, while providing robust information, can be economically and logistically prohibitive, particularly for species with cryptic behavior. Camera traps can be used to collect data at temporal and spatial scales necessary for estimating abundance, but the use of camera traps comes with limitations when target species are not uniquely identifiable (i.e., “unmarked”). Abundance estimation is particularly useful in the management of invasive species, with herpetofauna being recognized as some of the most pervasive and detrimental invasive vertebrate species. However, the use of camera traps for these taxa presents additional challenges with relevancy across multiple taxa. It is often necessary to use lures to attract animals in order to obtain sufficient observations, yet lure attraction can influence species’ landscape use and potentially induce bias in abundance estimators. We investigated these challenges and assessed the feasibility of obtaining reliable abundance estimates using camera‐trapping data on a population of invasive brown treesnakes (Boiga irregularis) in Guam. Data were collected using camera traps in an enclosed area where snakes were subject to high‐intensity capture–recapture effort, resulting in presumed abundance of 116 snakes (density = 23/ha). We then applied spatial count, random encounter and staying time, space to event, and instantaneous sampling estimators to photo‐capture data to estimate abundance and compared estimates to our presumed abundance. We found that all estimators for unmarked populations performed poorly, with inaccurate or imprecise abundance estimates that limit their usefulness for management in this system. We further investigated the sensitivity of these estimators to the use of lures (i.e., violating the assumption that animal behavior is unchanged by sampling) and camera density in a simulation study. Increasing the effective distances of a lure (i.e., lure attraction) and camera density both resulted in biased abundance estimates. Each estimator rarely recovered truth or suffered from convergence issues. Our results indicate that, when limited to unmarked estimators and the use of lures, camera traps alone are unlikely to produce abundance estimates with utility for brown treesnake management.

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Habitat type and structure affect trap capture success of an invasive snake across variable densities

Cited by 7 publications

References 42 publications

Spatial ecology to strengthen invasive snake management on islands

Spatial ecology to strengthen invasive snake management on islands

Contact rates with nesting birds before and after invasive snake removal: estimating the effects of trap-based control

Evaluation of camera trap‐based abundance estimators for unmarked populations

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