Daniel S. Vice

Objectives and integrated approaches for the control of brown tree snakes

The inadvertent introduction of the brown tree snake (Boiga irregularis) to Guam has resulted in the extirpation of most of the islands native terrestrial vertebrates, has presented a health hazard to small children, and also has produced an economic problem. Management of brown tree snakes is aimed at a number of objectives, the foremost of which has been to deter its dispersal through Guams cargo traffic to other locations. Another objective is to reclaim areas on Guam for reintroduction of native wildlife. A related objective is the protection of small sensitive sites on Guam from brown tree snake intrusion, such as power stations or nesting trees and caves. A fourth objective is to contain and capture incoming brown tree snakes at destinations vulnerable to their introduction. A final objective is to control incipient populations in other areas beyond their native range. A number of control tools have been developed, or are being developed. The efficacy of each control method depends on the situation to which it is to be applied. The control methods are described individually and the suites of methods most suited to each management objective are discussed.

Sustained evaluation of the effectiveness of detector dogs for locating brown tree snakes in cargo outbound from Guam

The accidental introduction of the brown tree snake Boiga irregularis to Guam has resulted in the extirpation of most of the islands native terrestrial vertebrates, has created a health hazard to infants and children, and has resulted in economic losses. The high brown tree snake population densities on Guam, the species’ adaptations for successful dispersal, and Guams position as a focal point for commercial and military cargo shipments have created a high level of concern that brown tree snakes could spread from Guam to colonize other vulnerable locations. Cargo inspections using teams of handlers and their detector dogs form the last line of defense for preventing brown tree snake dispersal from Guam. We assessed the efficacy of the teams of handlers and their dogs during 1998 and 1999 for locating stowed brown tree snakes by planting live brown tree snakes (in escape-proof containers) in cargo without the knowledge of the handlers inspecting the cargo. Many of these inspections were monitored by a concealed observer to determine the reason if a planted snake was not located by the dog teams. For 1998 and 1999, we found similar efficacies of 61% and 64%, respectively. When the snakes were not located by the dogs, we found that twice as many were missed because the dog did not change its behavior in response to the snake rather than because the handler did not conduct an adequate search pattern. During daytime inspections we found a greater efficacy for outdoor inspections than for indoor inspections. We found that the average efficacy of 62% for the 1998–99 period was lower than the baseline efficacy of 70% established in 1997.

A comparison of three trap designs for capturing brown treesnakes on Guam

The accidental introduction of the brown treesnake (Boiga irregularis) to Guam has resulted in the extirpation of most native terrestrial vertebrates on the island, thousands of power outages, and significant ecological changes. In addition, Guam now serves as a source population for the dispersal of snakes to other islands. Control of the brown treesnake is dependent upon the use of traps in a variety of settings, including port environments and in forested habitat. A variety of snake traps have been used on Guam; most consist of a modified crawfish or minnow trap, housing a live mouse that serves as a lure. We compared the efficacy of three trap styles: (1) a two-piece design with a separate internal mouse chamber; (2) a one-piece trap, with design improvements aimed at decreasing handling; and (3) the same one-piece trap, fitted with a PVC-coated wire-mesh entrance flap. Data collected included snake capture rates, snake size distribution, mouse survival, and trap maintenance time. Snake capture rates did not differ between the one-piece and the two-piece traps, although capture rates were significantly lower in the PVC-flap traps. The average snake size or distribution of snake sizes did not differ between the one-piece and two-piece traps. Handling times, both with and without a snake in the trap, were significantly lower for the one-piece trap. Mouse survival did not differ between the one-piece and two-piece trap styles. Our results indicate that the modified one-piece trap design provides several advantages over previous trap designs.

Recent Records of Alien Anurans on the Pacific Island of Guam

ABSTRACT Eight anuran species were recorded for the first time in Guam in the period May 2003–December 2005, all apparently the result of arrivals to the island since 2000. Three of the eight species (Rana guentheri, Polypedates megacephalus, and Eleutherodactylus planirostris) had well-established breeding populations by 2005. A further three (Fejervarya cf. limnocharis, Fejervarya cancrivora, and Microhyla pulchra) were recorded from a number of individuals, but it is not known whether these species have established breeding populations. Two species (Kaloula pulchra and Eleutherodactylus coqui) appear to be incidental transportations to the island that have not established. Before 2003, five anuran species, all introductions, had been recorded from Guam. Three of these, Polypedates leucomystax, Pseudacris regilla, and Kaloula picta, were detected on Guam in incoming cargo but destroyed. Two species established: Bufo marinus was deliberately introduced and the Australian hylid Litoria fallax was probably an accidental introduction. Successful establishment of anurans on Guam has increased the risk of frog introductions to nearby islands. By providing additional food sources for the brown tree snake (Boiga irregularis), anuran introductions have increased the chance that B. irregularis might substantially increase in numbers and in turn increase the risk of the snake being accidentally transported to other islands.

Brown tree snakes effectively removed from a large plot of land on Guam by perimeter trapping

Abstract The brown tree snake introduction to Guam has had serious environmental, economic and social consequences. Trapping brown tree snakes in the vicinities of ports and other cargo staging facilities is central to a program implemented to deter its dispersal from Guam. Trapping forested plots on their perimeters has been an efficient and effective trap placement strategy for removing brown tree snakes from plots up to 8.4 ha. Here we examined whether this trap placement strategy was effective on a 17.8 ha plot, over twice the size of plot for which there was solid evidence of perimeter trapping’s efficacy. We found that brown tree snakes were removed according to an exponential decay function. From 7 weeks on of trapping, snake captures had declined to low steady state levels that may best reflect population recruitment in the plot. After 22 weeks of trapping, both the plot interior and perimeter were trapped in a second phase designed to determine if the central portion of the plot contained reservoirs of brown tree snake populations. The second trapping phase lasted for 8 weeks and produced the same low, steady state capture rates as the final 16 weeks of the first phase that used only perimeter trapping. Only five snakes were captured in the plot interior in the second phase. We concluded that perimeter trapping removed brown tree snakes throughout the plot and the strategy could be applied to larger plots than demonstrated previously.

Standardizing the Evaluation of Brown Tree Snake Trap Designs

The introduced brown tree snake has had devastating impacts on the native vertebrate fauna of Guam. Trapping is the primary means by which brown tree snakes are removed, either in support of reintroduction of endangered species or to deter their movement from Guam in cargo. Traps used to control brown tree snake populations have been continually evolving since the 1980s. Before general operational implementation of a new design, the efficacy of new trap developments must be demonstrated. In this paper we combine the current knowledge about brown tree snake control objectives and practicalities, the information gained from a variety of brown tree snake trapping studies over the years, and fundamental statistical principles and methods to standardize procedures for testing developments in brown tree snake traps.