Boiga irregularis

Common Name: 
BROWN TREE SNAKE
Taxonomic Key: 
Reptiles
Legacy ID: 
2 530
Species Name: 
irregularis
Publication Title: 

Amphibian conservation: clarifications to comments from Andreone

FORT Contact: 
Erin Muths
Authors: 
Erin L. Muths, and Robert N. Fisher
Related Staff: 
Erin Muths
Publication Date: 
2017
Parent Publication Title: 
Oryx
Publication Type: 
Archive number: 
States: 

Pub Abstract: 

We appreciate the comments from Andreone (2016) regarding our proposed alternative strategy for addressing the amphibian crisis. Andreone recognizes the utility of an Incident Command System approach but doubts the feasibility of implementation at an international level. We stated in our original article, however, that ‘the feasibility of our suggestion is debatable, but our point is that radically different approaches are necessary to effectively manage the largest extinction event in modern history’ (Muths & Fisher, 2015). There are examples of where such top-down strategies are being applied; e.g. for the brown tree snake Boiga irregularis (Stanford & Rodda, 2007), and biosecurity planning for Micronesia and Hawaii (NAVFAC Pacific, 2016). Another example is presented by Andreone. In Madagascar a community-wide conservation plan has been developed complete with prioritization of specific actions (Andreone, 2016). As with any top-down strategy, challenges will surface, especially when making decisions that affect economics. We note this caveat in our article, and Andreone points out such issues in Madagascar, where there are mismatches in priorities between biodiversity conservation and civil needs. Our suggestion is that a new paradigm needs to be considered given the gravity of amphibian decline, and one option may be to take a global approach focusing on specific, major threats. Application of an Incident Command System would not necessitate competition with, or emasculation of, local conservation priorities or actions.

Publication Title: 

To cross or not to cross: modeling wildlife road crossings as a binary response variable with contextual predictors

Authors: 
Siers, S.R., R.N. Reed, and J.A. Savidge
Related Staff: 
Shane Siers
Bob Reed
Publication Date: 
2016
Parent Publication Title: 
Ecosphere
Publication Type: 
Archive number: 
States: 

Pub Abstract: 

Roads are significant barriers to landscape-scale movements of individuals or populations of many wildlife taxa. The decision by an animal near a road to either cross or not cross may be influenced by characteristics of the road, environmental conditions, traits of the individual animal, and other aspects of the context within which the decision is made. We considered such factors in a mixed-effects logistic regression model describing the nightly road crossing probabilities of invasive nocturnal Brown Treesnakes (Boiga irregularis) through short-term radiotracking of 691 snakes within close proximity to 50 road segments across the island of Guam. All measures of road magnitude (traffic volume, gap width, surface type, etc.) were significantly negatively correlated with crossing probabilities. Snake body size was the only intrinsic factor associated with crossing rates, with larger snakes crossing roads more frequently. Humidity was the only environmental variable affecting crossing rate. The distance of the snake from the road at the start of nightly movement trials was the most significant predictor of crossings. The presence of snake traps with live mouse lures during a portion of the trials indicated that localized prey cues reduced the probability of a snake crossing the road away from the traps, suggesting that a snake's decision to cross roads is influenced by local foraging opportunities. Per capita road crossing rates of Brown Treesnakes were very low, and comparisons to historical records suggest that crossing rates have declined in the 60+ yr since introduction to Guam. We report a simplified model that will allow managers to predict road crossing rates based on snake, road, and contextual characteristics. Road crossing simulations based on actual snake size distributions demonstrate that populations with size distributions skewed toward larger snakes will result in a higher number of road crossings. Our method of modeling per capita road crossing probabilities as a binary response variable, influenced by contextual factors, may be useful for describing or predicting road crossings by individuals of other taxa provided that appropriate spatial and temporal resolution can be achieved and that potentially influential covariate data can be obtained.

Publication Title: 

Invaded invaders: Infection of invasive Brown Treesnakes on Guam by an exotic larval cestode with a life cycle comprised of non-native hosts

FORT Contact: 
Bob Reed
Authors: 
Holldorf, Elden T; Siers, Shane R; Richmond, Jonathan Q.; Klug, Page E.; Reed, Robert
Related Staff: 
Page Klug
Bob Reed
Publication Date: 
2015
Parent Publication Title: 
PLoS One
Publication Type: 
Archive number: 
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Pub Abstract: 

BACKGROUND

Multiple host introductions to the same non-native environment have the potential to complete life cycles of parasites incidentally transported with them. Our goal was to identify a recently detected parasitic flatworm in the invasive Brown Treesnake (Boiga irregularis) on the remote Pacific island of Guam. We considered possible factors influencing parasite transmission, and tested for correlations between infection status and potential indicators of host fitness. We used genetic data from the parasite and information about the native ranges of other possible non-native hosts to hypothesize how it arrived on Guam and how its life cycle may be currently supported.

METHODS

We identified the parasite by comparing larval morphology and mtDNA sequences with other Pseudophyllid tapeworms. We assessed probability of infection in individual snakes using logistic regression and examined different factors influencing presence of parasites in hosts.

RESULTS

We identified the parasite as the pseudophyllid cestode Spirometra erinaceieuropaei, with all sampled worms from multiple snakes sharing a single mtDNA haplotype. Infection appears to be limited to the only freshwater watershed on the island, where infection prevalence was high (77.5%). Larger snakes had a higher probability of being infected, consistent with the chronic nature of such infections. While infection status was positively correlated with body condition, infected snakes tended to have lower intra-peritoneal fat body mass, potentially indicating a negative effect on energy stores.

CONCLUSIONS

We discovered that B. irregularis inhabiting a small area of forested habitat in a freshwater watershed on Guam are often infected by a novel parasite of Asian origin. While further work is needed, this species of Spirometra, itself a non-native species, likely depends on a suite of recently introduced hosts from different parts of the world to complete the life cycle. This baseline study provides little evidence of any effects on host fitness, but additional data are needed to more thoroughly explore the consequences of infection in this invasive snake population.

Publication Title: 

Invasive Brown Treesnake movements at road edges indicate road-crossing avoidance

FORT Contact: 
Bob Reed
Authors: 
Siers, Shane R; Savidge, Julie S; Reed, Robert N.
Related Staff: 
Shane Siers
Bob Reed
Publication Date: 
2014
Parent Publication Title: 
Journal of Herpetology
Publication Type: 
Archive number: 
States: 

Pub Abstract: 

Roads have significant impacts on the dispersal of wildlife. Although this poses a threat to the abundance and diversity of desirable flora and fauna, it also affords some opportunity for enhancing control of invasive species. Roads are the most common terrain features that may affect the rate of landscape-scale movements of invasive Brown Treesnakes (Boiga irregularis) throughout Guam. We radio tracked 45 free-ranging Brown Treesnakes in close proximity to two roads in Guam and recorded instances where daily relocations of snakes spanned roads. Then we reconstructed observed movement histories with randomized turning angles, which served as a useful null hypothesis for assessing the effect of roads or road edge habitat on Brown Treesnake movement patterns. Random walk simulations demonstrated that Brown Treesnakes crossed these roads at a rate far lower than would be expected if snake movement was random with respect to roads and road edge habitat. We discuss two alternative hypotheses for these results: 1) habitat gaps posed by roads physically or behaviorally restrict snake movement; or 2) road edges provide preferred foraging habitat from which snakes are reluctant to depart. Because roads often form the boundaries of jurisdictional and management units, the effects of roads on the movement of invasive Brown Treesnakes will influence the prospects for success of future landscape-level suppression efforts.

Publication Title: 

Factors affecting defensive strike behavior in Brown Treesnakes (Boiga irregularis) provoked by humans

FORT Contact: 
Bob Reed
Authors: 
Spencer, McKayka M., Lardner, Bjorn, Mazurek, M.J., Reed, Robert N.
Related Staff: 
Bjorn Lardner
Bob Reed
Publication Date: 
2015
Parent Publication Title: 
Publication Type: 
Archive number: 
States: 

Pub Abstract: 

Striking is a typical antipredator defense exhibited by many species of snakes. While trapping Brown Treesnakes (Boiga irregularis) on Guam, we observed that snakes most frequently struck at an approaching person at a site where snakes had been trapped, marked, and handled in the past. Using a combination of between-sites and within-site comparisons, we assessed if the propensity to strike was correlated with capture histories (both recent and long-term), snake size, body condition (a proxy to nutritional stress), sex, or tail condition (broken or intact), while controlling for confounding variables. We confirmed that propensity to strike was higher at the site where we had been conducting capture-mark-recapture for several years. However, we were unable to demonstrate a correlation between striking tendencies and individual recent or long-term capture histories. The only morphological covariate that had an effect on strike propensity was sex, with females striking more often than males. After removing the site effect from our model, we found that snakes missing parts of their tails were more likely to strike than snakes with intact tails. We have yet to identify the factor(s) that cause the pronounced difference across sites in snake propensity to strike, and data from additional sites might help elucidate any geographical patterns.

Developing and Testing Methods for Extracting Environmental DNA from Soil Samples, with Applications to Detection of Brown Treesnakes

Code: 
RB00CNJ.31
A Brown treesnake, Boiga irregularis. USGS photo.
A Brown treesnake, Boiga irregularis. USGS photo.
Abstract: 

This project uses eDNA methods to determine whether the presence of brown treesnakes can be detected from soil samples. Thus far, eDNA methods have focused on aquatic habitats detecting DNA in water samples. The ability to amplify DNA from soil samples would allow greater geographic utility of these methods, and would be logistically preferable because water samples require extensive filtering, cold storage in the field, and high shipping costs for large volumes of water. Further, eDNA from soil could be a useful tool for early detection and rapid response activities for species such as brown treesnakes that rarely use aquatic habitats and which threaten to colonize previously snake-free islands.

Biologist Discusses Brown Treesnake Rapid Response with Governor Torres of the Commonwealth of the Northern Mariana Islands

FORT Biologist, Adam Knox, met with the governor of the Commonwealth of the Northern Mariana Islands on the afternoon of January 19, 2016. During this meeting, they focused on providing his office with background information about the recent Brown Treesnake sighting and information on the survey/monitoring plan going forward. The Governor closed the meeting by thanking us for our efforts and pledging his full support for the inter-agency operation

FORT Biologist Talks to KKMP Radio about Brown Treesnakes

On January 7, 2016, Adam Knox, FORT biologist, spoke with KKMP Radio Saipan. During this interview Knox gave information about Brown Treesnake outreach and information as well as introducing the staff at the Guam field station and thanking the community for their support. Knox and other USGS biologists from the Guam field station are currently on Saipan conducting intensive searches after two snake sightings were reported by members of the public. 

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