In April of 2017, a two-year 6.5-mile fence project with a combination of hog-wire and deer mesh was completed, protecting 1,348 acres of native montane forest, valuable watershed and important habitat for some of Hawaiʻi’s most imperiled forest birds from invasive ungulates. This project’s objective was to significantly reduce, and remove primary threats posed to the existing native ecosystem throughout the Halehāhā Unit in the Alakaʻi plateau, and after a combination of proven and novel monitoring and animal control techniques, our efforts have resulted in the rapid removal of pig and goat populations where we are now focusing on approaches to removing the small population of black-tailed deer from the remote unit. These threat management actions also safeguard the plateau’s ability to provide crucial ecosystem functions, such as the capacity to continue to provide fresh water and to mitigate detrimental effects of flood and drought cycles.
The montane forest and bogs of this area support a high diversity of native plants, invertebrates, and endemic birds, including the endangered Akekeʻe (Loxops caeruleirostris), Akikiki (Oreomystis bairdi) and Puaiohi (Myadestes palmeri), and a species which is being considered for listing, the Iʻiwi (Vestiaria coccinea). The Halehāhā Unit has the greatest concentration of these rare forest birds and it is imperative for their continued survival that their habitat is protected and conserved. Our work in this area has involved monitoring since before the ungulate removal process began, where our results are already showing benefits towards the native plants, creating a more stable environment for future restoration activities.
This project is part of a larger conservation effort spearheaded by the DLNR Division of Forestry and Wildlife’s “Rain Follows the Forest Initiative” and the Kauaʻi Watershed Alliance (KWA) to protect 8,000 acres targeting six management units within the KWA boundary, including the East Alakaʻi, Drinking Glass, Koaie, Mohihi and private lands owned by McBryde Sugar Co. Ltd
Proposed methods are based on successful ungulate removal and vegetation monitoring conducted by The Nature Conservancy (TNC) staff in all management units.
a) Trail cameras: Installing cameras throughout the unit is crucial in every step of the ungulate removal process, even prior to fence construction in order to provide baseline information on ungulate activity. Once the areas of higher animal densities were determined, more game cameras were deployed in order to help calculate population more specifically by species. The trail camera data was used to index activity by month, and found a peak in animal activity corresponding to the end of the projected strawberry guava (Psidium cattleianum) fruiting season.
Equation for Index: Sightings Per Month / Number of Active Cameras That Month = Average Sightings per Month/Camera
b) Forward-looking infrared (FLIR): In order to complement on the ground game camera monitoring, the Forward Looking Infrared (FLIR) camera uses a thermographic camera that senses infrared radiation, making it easier to identify ungulates from the air through dense canopy. This strategy helps in the population estimates, density and distribution. FLIR surveys are used to estimate animal populations in the unit.
c) Pig Trapping: Pig traps are circular, and about 15 feet in diameter built with 4-foot hog wire panels and t-posts. The door to each trap is constructed of angle iron panel, set to close with gravity once a trigger has been tripped. The open top and natural ground floor employed in this design minimizes stress on the animals. Each trap was equipped with an automated bait station mounted on a tripod inside configured to hold at least 200 pounds of corn, approximately a two-week supply. For the first 3-5 weeks of ungulate control the traps were kept open to allow the resident pigs to grow accustomed to entering the traps and feeding. Following initial trap monitoring, field crews will begin to set the traps. Once activity was observed at a trap site, the trap was set on the first day of a field trip and checked for captures in each of the following days of the trip.
d) Vegetation and Ungulate Monitoring Transects: Baseline data on vegetation composition and condition, as well as ungulate damage was collected annually at the 100m2-plot level to measure management action outcomes.
e) Weed Control: From fiscal year 2011 to present, significant actions have been taken in mapping and controlling of priority habitat modifying weeds within the proposed management unit. The primary target species in this area are Kahili ginger (Hedychium gerdenarium), strawberry guava (Psidium cattleianum), and Australian tree fern (Cyathea cooperi). Knowledge about the density and distribution of target non-native invasive plant species has developed greatly from the initial monitoring to current monitoring stages. All the information collected on the ground is being used to prioritize contractual weed control for present and future management efforts as ungulates are removed from the unit.
While effective use of monitoring data led to the rapid and efficient removal of animals, proliferation and improvement of the techniques employed could reduce management timelines and lower costs for similar projects statewide.
The management strategy within the unit employed a combination of public hunting pressure coordinated and overseen by the state to assist with the initial reduction in the resident ungulate population. This was followed by baiting and trapping, relocations, and targeted hunting to remove the remaining animals.
TRAIL CAMERA DATA:
Beginning in December of 2014, five trail cameras documented animal activity within the western two thirds of the unit. The camera memory cards were checked in May of 2015 after collecting data for over five months. Pig and deer activity was highest on the cameras placed in the southwestern portion of the unit and goats were documented only on one camera near rugged topography. Towards the end of June 2018, the field crew had a total of nine active game cameras throughout Halehāhā, expanding to more areas where data had not been collected previously within the unit.
Image 1- Young black tail buck observing trail camera.
Image 2- Large boar scratching on a tree, attracted to the area because of the feeder shown in the background.
Fig.1- Index of pig sightings from trail cameras with dates for fence status, guava season and FLIR surveys.
Fig.1 shows the fluctuation in the average number of pig sightings per camera within the unit. Starting on December 2014 trail cameras were deployed but only two were functional and collecting data during peak guava season in 2015. This may have biased the data, but it does appear there was a seasonal aspect to pig activity, likely due to strawberry guava season. By June 2018, additional cameras were deployed, giving a total of nine cameras distributed throughout the unit. Pig activity was very low when the fence was closed. Results show that ungulate control was effective in reducing pig numbers to zero within the unit.
Fig.2- Map of trail cameras with graphs showing total number of ungulate sightings from each camera with duration of activity represented in months.
Shown in Fig.2, the ‘Near Waialae Stream Camera’ reveals the highest value of 576 total pig sightings. The ‘Goat Camera’ had the most diverse animal sightings, catching mostly goats, but also recorded some pig and deer photos.
Image 3- Feral pig photo from the FLIR device appearing 'hot' through the 'cool' forest landscape.
Fig.3- Helicopter FLIR survey routes.
Fig. 4- Animal density estimates collected from three FLIR surveys.
ANIMAL REMOVAL RESULTS:
Fig.5- Ungulate removal by control method.
Image 4- Large boar self-deporting from a fenceline trap to the adjacent public hunting area.
Fig.6- Vegetation monitoring plots and transects, traps, game camera locations and fence attributes.
Fig.7- Vegetation recovery measured at established plots within the unit through time.
Image 5- Dense vegetation on the inside of the unit vs. animal browsing on the outside.
Fern species most impacted through direct browsing are recovering within the unit, while the growth of the same fern is suppressed on the outside by heavy browsing.
Hawaiʻi Association of Watershed Partnerships (Katie Ersbak); Hawaiʻi Department of Land and Natural Resources- Division of Forestry and Wildlife Kauai Branch (Sheri Mann, Pat Porter); US Fish and Wildlife Service—Pacific Islands Fish and Wildlife Office (Michelle Clark); Kauaʻi Department of Water; Kokeʻe Resource Conservation Program (Katie Cassel, Spencer Kashiwa) KIA Hawaii (Jake Muise); National Tropical Botanical Garden (Ken Wood); Feral Animal Removal Experts (Greg Czar); Kauaʻi Forest Bird Recovery Project (Cali Crampton, Justin Hite, and many more); Airborne Aviation (Chris Currier)