Post-implementation assessment of novel rodent control devices for protection of high elevation endangered species at Hawai`i Volcanoes National Park

Coad, Heather
McDaniel, Sierra
Misajon, Kathleen
Forbes-Perry, Charlotte
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Pacific Cooperative Studies Unit
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Invasive 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 shrubland site. 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 digital strike
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Invasive rodent, self-resetting trap, endangered species
Coad, Heather, Sierra McDaniel, Kathleen Misajon, and Charlotte Forbes-Perry. 2017. Postimplementation assessment of novel rodent control devices for protection of high elevation endangered species at Hawai`i Volcanoes National Park . Technical Report No.#196. Pacific Cooperative Studies Unit, University of Hawai`i, Honolulu, Hawai`i. 18 pp.
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