The ‘Alalā (Hawaiian Crow, Corvus hawaiiensis), endemic to Hawai`i and once common in mesic forests of Southern and leeward Hawai`i Island, have been extinct in the wild since 2002, up until current reintroduction efforts started in 2016. To date, there have been two ‘Alalā releases in the Pu‘u Maka‘ala Natural Area Reserve, one in December 2016 and another in September-October 2017; the next release is scheduled for Fall 2018. The reserve occupies 7,570 hectares in the Puna and South Hilo districts on Mauna Loa, within the Kūlani area, on the island of Hawai‘i and will be the location of 'Alalā releases for the next 2-4 years (Figure 1). The threats that led to the extinction of this species in the wild likely include a combination of habitat loss and degradation, predation by introduced mammals, and introduced diseases such as Toxoplasma gondii. The adaptive management strategy of this project has allowed for changes in trapping methodology to reflect needs of released birds and reduce non-target effects of the trapping program.

Figure 1. Current predator control trapping at Pu'u Maka'ala Natural Area Reserve with Northern and Southern sections, traps, and release sites labelled. 

Rats and mongoose are known to depredate on bird eggs, nestlings, and fledglings and may be intermediate hosts of the parasite, T. gondii, which is known to cause fatal infection in ‘Alalā (Dubey and Beattie, 1988; Work 2000). There is potential for ‘Alalā to become infected if they consume infected animals. (Hutchinson et al. 1969). Feral cats are likely the most significant threat to ‘Alalā, through their demonstrated depredation of Hawaiian avifauna at various stages of development (Hess et al. 2004; Hess 2011), as well as their role as the definitive host for T. gondii (Wallace et al. 1972). These predators may also compete with ‘Alalā for food resources in their shared habitat.

The conservation goals of this predator control program are to:

• Reduce predation of ‘Alalā by introduced mammals 

• Reduce the risk of ‘Alalā mortality due to T. gondii

• Reduce rodent presence at feeding stations in the ‘Alalā flight conditioning aviary, release aviaries, or at supplementary feeding stations

• Implement the control program such that the non-target effects of the control do not negatively affect ‘Alalā (Gaudioso-Levita et al. 2017; VanderWerf et al. 2013)

Trapping 

Trapping started approx. 4 months prior to the 2016 ‘Alalā release and has continued year-round. Traps were placed on the landscape in grids, along 4x4 roads, or fence lines in the Northern and Southern sections of the Pu’u Maka’ala NAR (Figure 1). Trap types include Victor rat snap traps, Goodnature A24 traps, conibear #160 kill traps, and live cat cage traps (Tomahawk or Havahart brand) (see Figures 2-5 and Table 1). Trap lures varied and included: peanut butter, Goodnature rat lure (Long Life Chocolate Formula), a 1 x 1-inch square sponge soaked in fish oils with petroleum jelly based fish paste, dry cat food mixed with fish oils, wet canned cat food, sardines, and Cat Passion Lure. Due to the adaptive management approach to predator control, trap lines and methods differed in spacing and mounting height pre-and post-December 2016 ‘Alalā release and have changed for subsequent releases, based on staffing resources and release activities across the landscape. During the interim between release one and two when no birds were on the landscape, conibears were set on the ground. Conibears were completely removed in April 2018 due to changing ‘Alalā behavior and expanding live trapping around the perimeter of the Northern section.

Table 1. Trapping methods used in 2016 - 2018 by section of the NAR and site area.

Figure 2. Changes to conibear methods over time and 'alalā releases. From left to right: conibear on ground in forest grid pre-2016 release, conibear mounted 22” above ground on fencelines pre-2016 release, conibear mounted 3” above ground post-2016 release. 

Figure 3. Changes to live cage trap methods over time. From left to right: Live cage traps set in duplicate at 26 stations in Northern and Southern sections for pre- and post-2016 release; traps baited with fresh lure weekly with rotating lure every few months, added Cat Passion lure in 2018; expanded live cage trapping in the North pre-2018 release although most stations have a single trap (37 single stations in North and South), added shade cloth and tucked under brush to camouflage traps.

Figure 4. Changes to snap traps pre- and post-release. From left to right: metal boxes house Victor rat snap traps; boxes were camouflaged with paint and a 10 gauge wire was added to opening on each side to further exclude non-target animals post-release.

Figure 5. Changes to Goodnature A24 over time. From left to right: Pre-2016 no excluder, trap mounted the manufacturer recommended 12 cm above ground ; custom 4 inch flex pvc pipe excluder added to bottom opening of Goodnature A24, mounted 3 inches above ground to prevent non-target effects on ‘Alala; custom 1 x 1-inch wire mesh tube added to bottom opening of Goodnature A24, mounted 3 inches above ground.

Monitoring 

Monitoring of rodents was conducted on 500-meter long transects (with Release Site 3 being 550-meters long), 50 - 200 meters apart for Release Sites. Tracking tunnels were placed every 50-meters for Release Sites 1 and 2, and every 35-meters in treatment area with 50-meter spacing in control area for Release Site 3. All tracking tunnels were pre-baited one week prior to first run/activation (see Figure 6). The control tunnels are in locations at least 50-meters from rodent traps, and the treatment tunnels overlapped with the rodent control grid. The flight aviary has a modified monitoring grid of 25-meter spacing within the treatment area due to the small rodent grid scale, with 50-meter spacing of control tunnels (see Table 2). Tracking tunnels were run before trapping began (baseline), and are run every 3 months thereafter (see Gillies and Williams, 2013).  Note that the rodent grid at Release Site 1 was removed in mid-February 2017 but monitoring continued for an additional six months. 

Figure 6. Tracking tunnel with example ink card below.

Table 2. Rodent monitoring tracking tunnels by site, as of June 2018.
 

Monitoring of cats was conducted using motion-sensor trail cameras (see Figure 7), which were placed facing conibear traps, live cage traps, or on trails first using random spacing (Release Site 1 in 2016), then using standardized spacing at about every other live cat trap (2017 and 2018) (see Table 3; Rowcliffe et al. 2008; Glen et al. 2013). Semi-standardized spacing of cameras for release site 2 in 2017 consisted of five cameras spaced at every other live cat trap on the main road leading to the site. In 2018, the camera monitoring area expanded across the landscape in the Northern section of the NAR but were not spaced as closely (see Figure 1). Memory cards from the cameras are switched and reviewed every 2-3 weeks.

Figure 7. Trail camera Moultrie M-999i

Table 3. Cat monitoring cameras and spacing.

Statistical analysis

Animal captures are shown in a categorical line graph (see Figure 8). Capture rates for each trapping type used were calculated as: ((total # captures/ # trap nights) x 100), and this was calculated for each year of the project (see Table 4). Cat detections are shown by line graphs and spatial maps (Figures 12-15). 

Rat tracking was calculated by reading ink cards, and for additional rodent monitoring analysis, we conducted Pearson chi-square tests or Fisher's Exact Tests (when frequency <5) to compare the frequency of cards with and without tracks for rats for tracking tunnels (Figures 9-11). We conducted two-sample t-tests to compare the cat detection rates in North vs. South.