Brown Tree Snake (Boiga irregularis) — predicting the extent of the threat. 13


Summary: Predictive modelling shows the response of the BTS is an asymptotic function of precipitation, with no real upper limit. It would therefore be a threat to all tropical areas no matter how high the rainfall.

Resources: Controversial Topics — a source for new important information on Brown Tree Snake emerging from nightly searches for new images, web pages, videos, news articles and scientific articles.

The Brown Tree Snake (BTS) is a significant threat to many native species where it has invaded. There are a large number of ongoing efforts to prevent its movement into Florida, Hawaii, Texas, and other potential new habitats.

If brown tree snakes come here from Guam, they would cause “the greatest catastrophe of the century,” an federal official says.

The BTS (family Colubridae) belongs to the genus Boiga, a group of about 25 species that are referred to as “cat-eyed” snakes due to their vertical pupil. They are rear fanged, have a large head in relation to its body, brownish or greenish, sometimes faint bands. Adults are generally 4 -5 feet long. BTS can survive for extended periods of time without food, a trait that enables it to survive in ship-bound and stored cargo for long time periods.

BTS currently occur beyond their native range. They were introduced to Guam during World War II with a single female snake and spread to all parts of Guam by the late 1960s. Subsequently it has been shown they are responsible for a drastic decline in numbers of all native birds on the island.

BTS predictive model

The BTS point data were from a listing of the Australian Museum holdings provided by Gordon Rodda (personal communication 2005) compiled circa 1988 and transcribed to digital form by me. In all, there were 274 data points covering only the Australian and Papua New Guinean portion of the native distribution.

WhyWhere data mining was used to identify the most influential variables and, via study of the response curves, provide insight into way a species responds to its environment. The algorithm uses image processing methods to efficiently sift through large amounts of data to find the few variables that best predict species occurrence.

A habitat suitability map prepared for the BTS using data and WhyWhere model is shown below. The results of mining for the most important variables for predicting the distribution of BTS was:

Best accuracy 0.8402335 for variable lcprc03.raw
Leemans and Cramer March Precipitation (mm/month)

The distribution of the Brown Tree Snake predicted from March precipitation by WhyWhere. Blue is zero or low suitability, green to yellow is medium and brown to red is high suitability environment.

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0.226662291907846.png

This was a result of mining 528 terrestrials variables generally described here and specifically listed here.
The histogram of response of the species to environmental values is as follows:

The histogram of the response of the Brown Tree Snake (y axis) to classes of March precipitation (x axis). Blue bars represent the frequency of the precipitation class in the environment, while red bars represent the frequency of the BTS occurrences in that precipitation class.

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0.0633556216424722.png

It is clear that the response of the BTS is an asymptotic function of precipitation, with no occurrences at low March precipitation, and no real limit to upper precipitation. This is consistent with observations that BTS prefer a humid environment, and do not inhabit environments with chronic low humidity, and appear unable to shed properly when the relative humidity falls below 60 percent (Rodda et al. 1999).

Other resources related to the BTS on this site are the Controversial Topics — a source for new important information on Brown Tree Snake emerging from nightly searches for new images, web pages, videos, news articles and scientific articles.

References

RODDA, G. H., T. H. FRITTS, M. J. MCCOID, and E. W. CAMPBELL III. 1999. An overview of the biology of the Brown Treesnake (Boiga irregularis), a costly introduced pest on Pacific Islands. Pages 44-80 in Gordon H. Rodda, Yoshio Sawai, David Chiszar, and Hiroshi Tanaka, editors. Problem snake management : the habu and the brown treesnake . Cornell University Press, Ithaca, NY. 534p. 3,033KB

  • Wyandra

    This may seem like a truly strange suggestion but I live in Queensland and at least 3 times in the last year or so we have found large snakes dead in our back yard entangled in the netting used to keep the birds off our fruit trees.It seems to occur with any fine synthetic netting of about 2 inch square but might work as well with other fibres and guages. They get tangled up and die trying to escape without any deliberate effort required – and I have never seen a bird die in the same netting.

  • Anonymous

    This may seem like a truly strange suggestion but I live in Queensland and at least 3 times in the last year or so we have found large snakes dead in our back yard entangled in the netting used to keep the birds off our fruit trees.

    It seems to occur with any fine synthetic netting of about 2 inch square but might work as well with other fibres and guages. They get tangled up and die trying to escape without any deliberate effort required – and I have never seen a bird die in the same netting.

  • Wyandra

    This may seem like a truly strange suggestion but I live in Queensland and at least 3 times in the last year or so we have found large snakes dead in our back yard entangled in the netting used to keep the birds off our fruit trees.It seems to occur with any fine synthetic netting of about 2 inch square but might work as well with other fibres and guages. They get tangled up and die trying to escape without any deliberate effort required – and I have never seen a bird die in the same netting.

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