Technical Report #196.
Coad, H., S. McDaniel, K. Misajon, and C. Forbes-Perry. 2017. Post-implementation assessment of novel rodent control devices
for protection of high elevation endangered species at Hawai`i
Volcanoes National Park. 18 pages.
TInvasive species, including rats, threaten the
existence of many of Hawai`i’s native species pushing them to the brink
of extinction. Hawai`i Volcanoes National Park has a long history of
successfully managing ecosystems and providing rare species habitat
through systematic invasive species control. Landscape level rodent
control is prohibitively expensive; however, localized control has
proven cost-effective while providing significant resource benefit.
A trapping program using self-resetting Goodnature® A24 technology was
implemented at two remote sites in Hawai`i Volcanoes National Park in an
effort to protect five endangered plant species and three endangered
bird species from black rat (Rattus rattus) predation. This trapping
method has been successfully implemented on other islands, but
implementation requirements are site specific. Techniques and
maintenance schedules were investigated specifically for subalpine dry
shrubland environments and also high elevation wet forest environments.
Trap performance, recommended grid spacing, and a new chocolate long-life
lure formula were evaluated over the course of this investigation.
Apparent rodent control trends and subsequent native species responses
were captured over the course of four months by conducting biweekly trap
visits and analyzing motion triggered camera footage.
Clear declines in rodent activity were documented at each site during the
four month intensive monitoring period. At least 38 rodents were removed
from the subalpine dry shrubland test site during this period, while at
the high elevation wet forest site at least 102 rodents were removed. It
is suspected that the number of total kills was underestimated using
available monitoring techniques. Trapping activity appeared to prevent
major damage to flowers and diminish damage to fruit of endangered
Campanulaceae species at the forested test site, however it is unclear
what effect trapping efforts had on native bird species at the subalpine
Management recommendations differ by site. For subalpine shrubland sites,
trap spacing should not exceed 100m x 100m to control M. musculus or R.
rattus; tighter spacing may be necessary. In high elevation wet forests
spacing traps at 50m x 50m is recommended to effectively reduce R.
rattus populations. Pre-baiting traps is not advised to minimize
potential damage done by rodents gnawing on depressurized traps.
Concurrent trapping for feral cats and other scavengers, or strategic
trapping schedules, are recommended to mitigate potential secondary
predator attraction for sensitive sites such as Hawaiian petrel nesting
areas. Schedule of trap maintenance should include monthly lure checks
and ‘refreshment’ squeezes, regardless of site ecosystem. Scent of the
lure diminishes between refreshment visits in arid environments and may
be masked by algae or mold in wet environments. Use of the Goodnature®
automatic lure pump should be considered to potentially alleviate this
issue. In both environments standard lure bottles were found to last
through the 16 week monitoring period. Lure was found to remain
attractive to rodents, after refreshment squeezes as long as 36 weeks
after deployment at the forested site. Trap maintenance should be
scheduled to check CO2 status no later than 12 weeks after deployment,
regardless of site ecosystem, to detect exhausted CO2 or malfunctioning
traps, and at monthly maintenance visits if possible. Use of a surrogate
pest such as a rubber rat to test fire through the trap shroud is
advised to accurately simulate a strike, and ensure functionality of