Research Efforts to Enhance Control
Excerpted from Department of the Interior "Integrated Pest Management Approaches to Preventing the Dispersal of the Brown Treesnake and Controlling Snakes in Other Situations" 1999.
The dilemma of controlling or eradicating the brown Treesnake outside its native range has initiated detailed research in a previously unknown phenomenon: extirpation of native wildlife by an introduced snake. As human commerce and travel continue, the chances of brown Treesnakes and other species becoming established in new lands remains and will undoubtedly increase. In the interest of maintaining the biodiversity of these areas, it is necessary to understand the dynamics of the situation and find or create a means of control. A method to effectively reduce the population of snakes on Guam will take many years to develop because snakes are so numerous and widespread, and because of the difficulty in locating and trapping this highly cryptic, generalist, nocturnal snake. Working toward this goal, a number of topics have been and continue to be the focus of ongoing research. These include: developing an attractant and toxicant that works on the brown Treesnake without endangering other animals, people, or the surrounding environment; continuing to improve barrier development and expanding the number of islands employing such defenses; refining methods to capture smaller snakes (which are not easily captured in typical traps); identifying methods to control newly established populations; continuing to develop chemical fumigation and thermal treatment protocols to kill snakes in export cargo; researching the possibility of controlling snake reproduction and maturation through microbiology studies; and exploring other possibilities for biological control of the brown Treesnake. More details on each of these areas are listed below:
1. Development of attractants, baits, and toxicants
The development of artificial attractants and baits for the brown Treesnake is a high priority with many potential uses in a control program. However, the complexity of the cues used by snakes in evaluating potential prey is grossly underestimated by the general public, and significant obstacles exist. Although no obvious successful inanimate attractant has been developed to date, several breakthroughs show potential for the future. Snakes show some attraction to bird droppings, blood products, and lipids. On occasion, they will consume objects that do not resemble normal prey (e.g., meatballs and chicken bones). However, matching the desirable balance between chemical, thermal, and visual cues presents an ongoing research challenge before a truly artificial attractant or bait can be used. Once an attractant or bait is developed, it would greatly decrease labor costs required for trapping. Artificial attractants and baits could be used instead of live mice and lizards, which could facilitate the delivery of toxicants and promote the use of biological control agents.
2. Continued barrier development, with an emphasis on specific field applications and non-encompassing barriers
A variety of barrier designs have been shown to be effective in reducing movements of snakes under laboratory and small-scale outdoor conditions. At present, further enhancement of barrier technology is focused on engineering studies to reduce vulnerability to accidental damage (such as storms or human activities), to reduce costs of deploying barriers over distances needed for practical control situations, and to gain acceptance by appropriate use groups. Recent tests of pre-stressed concrete barriers available through local contractors have been successful, and several demonstration applications of barriers are planned in the near future.
3. Development of methods to capture smaller snakes, which may be less effectively trapped using present methods
Better traps and control methods for small snakes are needed to achieve maximal control success of juveniles, which are the most numerous size class in most snake populations and the most likely to disperse into and via the transportation network. Unfortunately, these are also the most difficult snakes to detect when visually searching an area and the most likely to escape from a trap. This research complements the work on attractants and baits and demonstrates broad application possibilities in snake control.
4. Development of methods to control newly established, low-density populations
The special problem of locating and capturing snakes in newly established populations is being investigated in field studies on Saipan and Guam at present. To prevent problem populations and maximize the probability for eliminating new populations, control strategies need to be implemented before dense populations develop. Ultimately, as dense populations on Guam are reduced in the contexts of protecting cargo, wildlife, or human environments, control of the remaining low-density populations will provide critical information toward maintaining control successes and delaying population recovery.
5. Continued development of chemical fumigation and thermal treatment
Although considerable work has been done and progress is evident on chemical fumigants, more work is needed to define alternative chemicals and possible thermal treatments of cargo. Either has the potential of being used as a means of forcing snakes from cargo or killing them in situations where removal would be difficult or prohibitive in terms of time or effort. The most appropriate means for use of these tools would be the combined use of chemical and thermal fumigation.
6. Special focus on issues related to reproduction, reproductive inhibition, and factors affecting juvenile survivorship, growth, and maturation as these factors apply to population levels and predatory pressures within terrestrial island ecosystems
Work on these biological processes offers the potential to turn the biology of the snake against itself. Effective control of reproductive processes, reductions in juvenile survivorship, etc., could be efficient ways to reduce the need for other control approaches. Work on reproduction is being accelerated with increased funding from the Departments of the Interior and Defense to the USGS and Wildlife Services (Research).
7. Exploration of options for biological control of established brown Treesnake populations
The potential exists for attaining some degree of control in the way of reductions using pathogenic organisms (disease agents, parasites, etc.). Preliminary work on viral agents is currently underway at the National Zoological Society in Washington, DC. Study of the critical characteristics of potential biological controls is underway by academic cooperators at Princeton University working with the USGS National Wildlife Health Center.