Biology Reference
In-Depth Information
render eradication extremely unlikely. Hence, efforts are now focused on identifying
effective techniques (mainly trapping) so that long-term control may at least be initi-
ated against what is likely to be a significant environmental pest. This work is made
more important by recent work suggesting that this species may survive weather con-
ditions across large portions of the United States (Rodda et al., 2008).
Long-Term Control
Far and away the largest-scale control operation for any alien reptile or amphibian
has been the United States' federal program on Guam to keep brown treesnakes
from spreading to other Pacific islands. This interdiction program was initiated in
1993, is ongoing, and will likely be needed in perpetuity. Most effort has gone
toward (1) reducing snake densities in areas surrounding air- and seaports, so as to
decrease their probability of entering cargo and vehicles, and (2) searching out-
bound cargo and vehicles for hitch-hiking snakes, so as to reduce probability of
shipping infested cargo. Population reduction largely depends on employing a
dense array of traps to capture snakes, which are then dispatched with prejudice
(Engeman and Vice, 2002). Nighttime searches of fences, which tend to be attrac-
tive to the snakes as easily traversed highways, also help lower snake numbers
(Engeman and Vice, 2001). Cargo searches largely rely on the use of trained dogs
(Engeman et al., 1998, 2002), but port workers occasionally find and kill them as
well. Reduction of rat populations through use of bait stations also lowers prey
populations around ports, increasing the efficacy of snake traps. This program has
been responsible for a considerable reduction in the numbers of brown treesnakes
leaving Guam and arriving in other jurisdictions, such as Hawaii. Although this
program is, strictly speaking, a prevention program designed to protect other
islands from infestation by brown treesnakes, it has generated numerous spinoff
tools that are directly applicable to control of these snakes on Guam. First, there has
been considerable refinement of effective trapping (Rodda et al., 1999d; Engeman
and Vice, 2002) and barrier (Perry et al., 1998a; E. Campbell, 1999) methodologies
to reduce snake numbers in the geographically restricted areas around the ports and
within cargo. These methodologies could be at least partly useful for rapid contain-
ment and eradication of brown treesnake incursions elsewhere. Second, considerable
work has proceeded on devising attractants (Shivik and Clark, 1999; Shivik et al.,
2000; Jojola-Elverum et al., 2001), repellents (Savarie and Bruggers, 1999; Clark
and Shivik, 2002), toxicants (Brooks et al., 1998a-c; Savarie and Bruggers, 1999;
Savarie et al., 2000, 2001, 2005), and toxicant-delivery systems (Shivik et al., 2002;
Savarie and Tope, 2004) to control brown treesnakes at both local- and
landscape-level scales (cf. Rodda et al., 1998). Management objectives and
applications for each of these tool sets are summarized in detail by E.W.
Campbell et al. (1999) and Engeman and Vice (2002). It has been recognized
for several years that removal of brown treesnakes from relatively small areas
(up to ca. 50 ha) may proceed effectively using existing barrier and trapping
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