Biology Reference
In-Depth Information
methodologies (Rodda et al., 1999e, 2002). Doing so could be important for
short- to medium-term conservation of some of Guam's endangered wildlife;
however, for long-term conservation of this biota, control across larger areas is
necessary. For control of snake populations across Guam's landscape, work has
progressed to the point that a methodology employing large-scale aerial delivery of
frozen pinky mice laced with acetaminophen has been evaluated for safety
(Johnston et al., 2002) and is being tested for efficacy (Hall et al., 2007). The expec-
tation is that once efficient delivery of large numbers of these baits is better refined,
clearance of brown treesnakes from certain landscapes on Guam will allow for
re-introduction of endangered native animals to these areas as well as greater secu-
rity from these pests in port areas. To reach this point has taken over 20 years of
research effort and 12+ years of operations effort. Costs of the research and opera-
tions programs for brown treesnakes are difficult to obtain, but US$17.9 million
was spent on snake-control operations on Guam from October 2001-September
2007 (M. Pitzler, United States Department of Agriculture/Wildlife Services,
personal communication, 2007).
Numerous credible reports and recovered specimens of brown treesnakes have
appeared on Saipan, in the Commonwealth of the Northern Mariana Islands, in the
past 20 years. However, attempts to recover snakes from these various sightings so
as to assess whether an incipient population is established have proven frustratingly
difficult. Dissatisfaction with this state of affairs led to the initiation in early 2007 of
an intensive three-week trapping and search effort in an area having multiple snake
sightings over the past 25 years, so as to determine whether an incipient population
could be detected (Hawley and Stanford, 2007). Trapping employed 185 traps, cov-
ering approximately 6 ha. Visual and canine searches occurred every night, employ-
ing 16-23 searchers/night (J. Stanford, United States Geological Survey, personal
communication, 2007). Total effort comprised 5,775 trap nights, 1,660 visual search
hours, and 100 canine search hours, with search effort summing to approximately
300 km of forest edge and forest transects; cost for the exercise was approximately
US$89,000 (J. Stanford, United States Geological Survey, personal communication,
2007). Results were negative, although it is uncertain whether this is because an
established population is absent or because its members are untrappable because
high prey abundance renders traps ineffective. Either way, the scale of effort
involved well illustrates what is required to competently assess suspected new incur-
sions of cryptic herpetofauna, even for narrowly circumscribed areas.
Control operations elsewhere have generally been sparse or gone unreported in
the scientific literature, but some information can be found in unpublished govern-
ment reports. Such activities as do occur typically involve attempted removal of a
species from a particular, limited area, often in an effort to preserve ecological values
for native species in high-quality habitats. Such efforts as I am aware of have fared
no better than many of the eradication projects noted above. An early attempt to
remove a population of
Caiman crocodilus
in southeastern Florida (Ellis, 1980)
appears to have failed (L.D. Wilson and Porras, 1983), and the population is now
well established (Meshaka et al., 2004a). Migration from adjacent source areas may
have been a contributing factor in this failure. Attempts to remove bullfrogs from a
