Eradication of feral goats and pigs and consequences for other biota on Sarigan Island, Commonwealth of the Northern .

C. C. Kessler 4815 Saddle Ave., Flagstaff, AZ 86004. USA

Abstract Sarigan Island (c.500 ha) is one of the 15 Mariana Islands in the tropical western Pacific Ocean. The native forest on Sarigan was in an advanced state of decline due to the presence of feral goats (Capra hircus) and pigs (Sus scrofa). During January and February 1998, 68 pigs and 904 goats were removed by helicopter shooting, ground shooting, trapping, and tracking with dogs. The goal was to stop and reverse the loss of forest and accompanying erosion and thus improve habitat for the endangered (Megapodius laperouse) and other native . Follow-up control in 1999 and 2000 removed an additional six goats. Sarigan Island is now considered free of feral ungulates. Vegetation monitoring before and after eradication shows an increase in plant species richness, an increase in tree seedlings, and the rapid expansion of the introduced vine Operculina ventricosa. also increased, but numbers of fruit bats, land birds, and rats have not yet showed change. It is still undetermined as to what effect the vine Operculina ventricosa will have on the regeneration and expansion of the native forest.

Keywords Vegetation; megapode; Operculina ventricosa.

INTRODUCTION means to improve habitat (through vegetation recovery) Of the 11 islands in the Mariana chain (15 islands total) for endangered Micronesian megapodes. that are uninhabited, the largest five have feral . The uncontrolled existence of these populations jeopard- METHODS ises the continued existence of the unique native plant and wildlife species on these islands. Entire forests are disap- Study area pearing and ecosystems are being changed before they are even understood. Some form of programme, either peri- Sarigan Island is a relatively small uninhabited island of odic control or total eradication, needs to be implemented about 500 ha located 121 miles north of in the Com- before irreversible damage is done to the entire system. monwealth of the (CNMI) (16o 42’ N 145o 46’ E). This island is a with Sarigan Island had been cultivated and maintained for steep slopes and no protected beaches. In the central-north- copra production in 1900 (Fritz 1902). Feral goats (Capra west portion of the island lies a level , which again hircus) and pigs (Sus scrofa) have been present on Sarigan rises steeply up the main cone. The south and east sides for at least 50 years according to Mr Yamamoto (pers. are extremely steep and rise continually to the top of the comm.), a 1940s resident of the island. All residents were island (549 m). The vegetation (Ohba 1994) consists of evacuated in 1945. In 1950 a request was made to the U.S. coconut trees (Cocos nucifera) with patches of hibiscus Navy administration to let Mr Palacious and company re- (Hibiscus tiliaceus) on the lower slopes of the west and turn to the island and commercially harvest goats (J. north sides. The upper plateau is half native forest (up- Johnson pers. comm.); permission was denied. It is be- land mesic climax) and half short grass (Chrysopogon lieved that ungulate populations were semi-controlled aciculatus). The slopes on the south and upper west sides through sporadic harvesting until the 1970s when the most are swordgrass (Miscanthus floridulus). The main cone is recent attempt at human colonisation was abandoned. Other swordgrass on the southwest and ferns (Pteris sp.) on the visitation/harvesting has consisted of brief stops by fish- northeast, with some remnant native forest scattered in erman or government scientific trips. ravines and crevices. There are no streams or free-stand- ing water. The combination of feral goats and pigs has had a severe impact on the native flora and fauna. It appears that the Timeline feral ungulates were changing Sarigan from a tropical for- est to a grassland habitat (Ohba 1994; unpub. reports Between 1995-1997, CNMI-Division of Fish & Wildlife CNMI-DFW 1988-1997). This alteration of habitat was (DFW) formulated a five-phase plan to eradicate pigs and believed to be adversely impacting endangered and re- goats on Sarigan: source species such as the Micronesian megapode (Megapodius laperouse), Mariana fruit bat (Pteropus v Phase I - Reconnaissance and survey mariannus), and coconut crab (Birgus latro) as well as v Phase II - Base camp establishment other native species. The primary goal of this project was v Phase III - Shooting programme to remove the feral ungulates from Sarigan Island as a

Pages 132-140 In Veitch, C. R. and Clout, M. N. (eds.). Turning the tide: the eradication of invasive species. IUCN SSC Invasive Species Specialist Group. IUCN, Gland, Switzerland and Cambridge, UK. Kessler: Eradication of goats and pigs, Sarigan Is v Phase IV - Removal of remnant populations/individu- als Bats v Phase V - Follow-up monitoring and re-surveying Fruit bats were surveyed by various biologists using dif- CNMI-DFW established 13 photo vegetation plots and ferent methods. Fancy et al. (1997) and Morton et al. completed a general aerial reconnaissance (including pho- (2000) used Variable Circular Plot (VCP) counts. Wiles tographs) in mid February 1997. Phase I was completed in 1983 and 1999 (Worthington 2001) and Johnson in 2000 with the help of a US Geological Survey-Biological Re- (unpub. report CNMI-DFW 2000) used station counts, search Division (USGS-BRD) bird survey crew in March individual sightings, and colony counts to estimate 1997 that resulted in baseline data on vegetation, bird, bat, populations. These different methods have been combined and populations (Fancy et al. 1999; unpub. report to form an estimate. CNMI-DFW 1997,1998). Birds Phase II, base camp establishment, was generally com- pleted by July 1997. During this period four 3 m x 2.5 m x Bird surveys on Sarigan were conducted using standard 2.5 m weatherproof containers, purchased by DFW, were VCP methodology. Different surveyors used either VCP flown onto the island by U.S. Navy helicopter. DFW per- (Fancy et al. 1997) or fixed-radius (Morton et al. 2000) sonnel then moved equipment and supplies into these con- analytical techniques to estimate densities. Due to the in- tainers over a period of several months. herent differences between techniques, only the “birds detected per station” were compared. Surveys were done Zoology Unlimited was contracted (for USD180,000) by in September 1990, March 1997, July 1999, and July 2000. the Fish and Wildlife Service through an Dr Justine de Cruz of CNMI-DFW compiled data and agreement with the U.S. Navy and CNMI, to conduct conducted the July 1999 and July 2000 surveys (unpub. phases III and IV. We began Phase III on 1 January 1998 report CNMI-DFW 1999, 2000). with helicopter shooting followed by ground hunts. This gradually shifted into Phase IV by the beginning of Febru- Rats ary. Phase IV ended by 1 March 1998 when it was be- lieved all ungulates had been removed from the island. Pacific rats (Rattus exulans) were trapped using a large All personnel had left the island by 2 March 1998. snaptrap baited with peanut butter and set on the ground. Thirty traps, spaced every 25 metres, were set on the ground Phase V, the monitoring phase, began in August 1998. This in two separate transects for a total of 60 traps. Traps first trip was conducted by CNMI-DFW. Three additional were left overnight and checked in the morning. Rat trap- monitoring trips in January and July 1999 and July 2000 ping was done in July 1999 and July 2000. Scott Vogt of were made (unpub. report Zoology Unlimited for USFWS- CNMI-DFW conducted surveys and provided data (pers. Honolulu 1999, 2000). During these monitoring trips data comm.). on habitat and wildlife was also collected by various bi- ologists. Monitoring of wildlife populations and surveil- lance for any surviving goats or pigs is ongoing. Glueboard traps were used for catching lizards. A line of Vegetation and wildlife monitoring 12 traps, with 5 m spacings was set in the morning and picked up in the afternoon. Traps were set in the shade in Vegetation both the coconut forest and native forest. Catch rates were expressed as the number of lizards captured per trapping In February 1997, one year before the eradication started, hour. Scott Vogt of CNMI-DFW conducted surveys and 13 permanent vegetation plots were established. These provided data (pers. comm.). were marked with steel bars and the Universal Transverse Mercator (UTM) coordinates were located using a Global RESULTS Positioning System (GPS) (unpub. report Zoology Unlim- ited for USFWS-Honolulu 2000; unpub. report CNMI- Overall we removed 904 goats (with a sex ratio of 2.38 DFW 1997). Photos of the plots were taken which in- females to every male of the 383 we sexed), 68 pigs (2.06 cluded two 3 m poles spaced five metres apart for scale. females to every male of the 55 we sexed), and two cats in All plant species within a 2 m2 area centred on the rebar the first 60 days. A further six goats were removed during were identified. Ground cover within the 2 m2 area was the four follow-up trips to the island; a density of 1.83 visually estimated as was canopy cover. Trees were sur- goats/ha and 0.14 pigs/ha. The four follow-up trips were veyed using the point-quarter method. Plots were spaced made in August 1998, January 1999, July 1999, and July 100 metres apart and followed a transect that cut across 2000. Each trip was an average of five search days. These the centre of the island starting in grassland, continuing trips accounted for one, four, one, and zero goats respec- through native forest, and ending in the coconut forest. tively (four females and two males). No pigs were ever Plots were re-surveyed in August 1998, July 1999, and encountered during follow-up trips. July 2000 and Laura Arriola of CNMI-DFW did analysis and graphs (unpub. report CNMI-DFW 1998-2000).

133 Turning the tide: the eradication of invasive species

Table 1 Effort and feral ungulate kills for Helicopter operations concentrated on those areas that had Sarigan Island, CNMI. 1 January to 28 February no or little canopy cover. The forested areas were searched, 1998. but proved too difficult to shoot through the canopy. Vari- ous methods of helicopter deployment were used. These Operational tactic Hunting effort Goats Pigs included dropping off a shooter near a cave or dense veg- (estimated) killed killed etation and directing the shooter through helicopter sur- veillance. Initial aerial 21 hrs flying 344 0 Ongoing aerial 9 hrs flying 26 0 Ground shooting Initial line sweeps 85 man-hours 126 5 Initial dispersed hunt 362 man-hours 382 25 After the initial seven days of aerial hunting we began the 2nd line sweep + dogs 97 man-hours 13 9 ground hunting part of the operation targeting goats, pigs 2nd dispersed hunt + dogs 424 man-hours 13 22 and feral cats. Our first tactic, used over the first two days, Pig snares/shooting 20 man-hours NA 7 was to use a line formation of nine hunters, without dogs, Judas goats 20 man-hours 0 NA that searched all forested areas. Follow-up survey #1 unknown 1 0 *Follow-up survey #2 210 man-hours 4 0 Shooters were deployed in a skirmish line spaced roughly *Follow-up survey #3 380 man-hours 1 0 30 yards apart moving across-slope following the general *Follow-up survey #4 380 man-hours 0 0 contour. All personnel were in constant communication through the use of hand-held radios. As shooters moved * Includes hours of all wildlife biologists surveying and shooters. through the forest they stayed in visual contact with the person on either side, helped by the safety requirement to Aerial shooting wear orange vests and hats. If they became separated due to terrain or dense vegetation or if they spotted animals, they would use the radios to communicate a desired coor- The helicopter (Macaw Helicopter Services, Saipan, R. dinated action (i.e. stop or slow down). At the end of the Crowe-pilot, flying a Hughes 500) was used for about three day all shooters were debriefed to record the number of hours/day over the first seven days of the operation begin- animals shot, number seen and in what area, tactical points, ning on 1 January 1998, and sporadically thereafter until and any other items of interest. These line formations 22 February 1998. In total 370 goats were shot from the worked well for goats but not for pigs because the latter helicopter (41% of the population) in a total of 30 flying- tend to break back through the skirmish line making a shot hours, of which 344 were killed during the first seven days dangerous. in 21 flying-hours. After two days of this large line-shooting operation, the The overall plan was to shoot as many goats as possible crew was reduced to about five shooters (varied from one from the helicopter and then follow this with ground hunt- to seven). They were deployed in various ways to best ing. No pigs were ever shot from the helicopter. One to exploit the terrain and goat behaviour. Often they would two shooters and a spotter conducted helicopter opera- target a specific area, set up one or more spotters/shooters tions. The spotter was useful in tallying numbers and keep- at a strategic point (i.e., a choke point or exit trail), then ing goats in sight when herds broke up. Shooters were the rest would disperse through the area. This worked well armed with either a semi-automatic rifle with scope and a for the small isolated groups of goats left. Again, radios large-capacity magazine or a bolt action rifle with scope. were essential to keep information flowing as to the progress being made and if help was needed. Positions of the various shooters were continually monitored to ensure coverage and safety. This second tactic continued for about three weeks, after which the crew was again increased to 11 shooters and line sweeps were repeated. At this time we also used dogs. Trained to chase pigs, these dogs also helped with the goats. This greatly increased our cover- age and allowed us some certainty that an area was goat or pig-free. After five days of clearance by the second round of line sweeps, the crew was again reduced to five per- sons. These five were dispersed singularly about the is- land with the primary mission of detecting goats or pigs. Once detected, help was then radioed for and a coordi- Fig. 1 Goats (Capra hircus) shot over time per nated action deployed. The goats’ behavioural trait of stay- operational tactic. Black triangles show the ing in a home range was exploited and made them vulner- number shot from helicopters and black dots able to this type of operation. Often goats could be de- the number shot by ground hunting. Sarigan tected by the bleating of the kids. Also the goats’ habit of Island, CNMI. going into open areas to feed made them more observ-

134 Kessler: Eradication of goats and pigs, Sarigan Is able. It should be cautioned that goats could detect loud about a total eradication. Dogs arrived on 3 February 1998 radios and would flee. Our biggest problem in finding goats and began hunting immediately. Hunting with dogs ac- was their use of caves. We could sweep an area, but could counted for the last 46% (31) of the total. The last pig was never fully check all the caves and crevices in the volcanic killed on 28 February 1998. terrain. Toward the end of the project we would smooth the ground along trails and in caves to be able to better Control techniques detect tracks. Snaring for pigs Goats were found in all habitats other than about 100 ha of swordgrass, giving an effective density of two goats/ha. Snares were deployed but found to be of limited use. Two This grass grows in dense clumps to about 3 m in height. kinds were used, a commercial wire snare and a locally- As its name implies, it can inflict many slight cuts to ex- constructed foot snare used with bait. The commercial posed skin. This unpleasantness, plus its density and sti- wire snare was a constricting type equipped with a one- fling heat, render it practically impenetrable and make for way continually tightening device. These are placed on extremely disorienting and strenuous hiking conditions. trails and require that the animal put its head into it. These Thus it was decided to burn off the Miscanthus. This was were not effective due to the lack of defined pig trails. consistent with local agricultural practices. The two main The local snare was moderately successful. This snare reasons for doing so was to deny fleeing animals cover was tied to an elastic tree branch, which would be bent and allow easier traversal by foot (access into remote ar- down and fastened to a trigger. The snare loop would then eas). Miscanthus was usually ignited with a flare shot from be placed on the ground in front of a small semi-circular a marine signal gun out of the helicopter. In most areas the enclosure made of cut tree limbs that held the bait. The Miscanthus burned quickly, and did not spread into forested pig would stick its head into the enclosure’s opening for areas. It was our practice to go and investigate any carcass the bait while standing in the snare’s loop. The pigs feed- we found in the burned areas. We were curious to know if ing would release the trigger, the snare would tighten on any animals died from the fire. We were always alerted to one foot, and the branch’s action would suspend the foot dead animals by the flies. Our only discoveries were of in the air thus holding the pig. Bait was split coconut. A monitor lizards and geckos. As these were not totally con- more effective method was to bait a large area with split sumed by the fire, it is assumed that anything larger would coconuts and return at night with the use of a spotlight to have left a greater proportion of carcass and would have shoot any pigs feeding. For the first 30 days snaring, shoot- been discovered more readily. It is therefore our conclu- ing over bait, and hunting were the only methods used for sion that no large animals or birds perished in this manner. pigs. We had just about reached our limit; that is to say that we were no longer removing pigs, when the pig dogs Pigs were brought to the island.

Pigs were restricted to the native and coconut forested ar- Dogs eas, about 162.5 ha (Morton et al. 2000), giving an effec- tive density of 0.42/ha in these habitats. For the first 30 The pig dogs used were a local nondescript breed (mutt or days pigs were hunted opportunistically by personnel, in- “boonie” dog), about 34 kg apiece, and came from cluding baiting and snares. This accounted for 54% (37) Island in the Mariana chain. Dogs worked well, of the total pigs. At the end of 30 days we concluded that but could only chase a maximum of four pigs in a day pigs were not being removed efficiently enough to bring before they were tired out. Two pigs in a day was more the norm. Chasing down pigs with dogs is a high-adrenalin pursuit that requires the shooter to strip down to the bare essentials. All gear must be tightly attached to the person, and protective eyewear is recommended. Gear consisted of a radio, canteen, and a short-barrelled semi-automatic rifle. As soon as the dogs signal that they have detected an animal, the shooters must start to run in the general direction so as to keep up. This physically exhausting and mentally nerve-racking run eventually ends in a limited access area. The pig’s habit is to run until tired, then turn and face the dogs. When they do this, some natural bar- rier (such as thick brush or a ravine bank) usually protects their back. The shooter, upon arriving at the scene, is usu- ally found to be blocking the exit path. As soon as the pig becomes aware of the person, it will try to run again and Fig. 2 Pigs (Sus scrofa) shot by hunting will charge through anything in its way. In this way the without dogs (black squares) and hunting with shooter is often attacked. Usually the shooter can dispatch dogs (black diamonds) over project duration. the pig before it knows a person is there by slowly ap- Sarigan Island, CNMI. proaching. If not, then the dogs will charge in at the move-

135 Turning the tide: the eradication of invasive species ment of the pig and attempt to hold it. This all makes for by both preventing dangerous shooting conditions and fa- some seconds of utter confusion. After the pig is shot, a cilitating rescue for possible accidents. Each person car- long break is required to rest the dogs and calm the shooter. ried a unit plus a spare battery. Some of the units failed The dogs usually held smaller pigs. These dogs would due to the high humidity and by getting soaked with per- also detect and chase goats, although they did not seem as spiration. Waterproof or “integrally safe” type radios are enthusiastic and would stop chasing once the goats reached double the standard price, but they may be well worth ob- an area of cliffs, boulders, or sharp rocks. taining. We did lose or otherwise destroy a few units and it is recommended to have extras on hand. Power from a gas Radio-collared goats generator was used for re-charging. For field operations, radios should be firmly attached to the shooter in a man- On 12 February six radio-collared goats were released. ner that is easy to use (i.e. close to the face) but secure. These were airlifted to different sections of the island. They Plastic ziplock freezer bags or waterproof radio bags should were heavily marked with water-soluble pink dye on their be carried to cover units during rain. hair, carried pink flagging in their horns, and a pink-flag- ging collar for identification at long range. It was feared Communications between Sarigan and Saipan (location of that these animals would be inadvertently shot, thus the closest facilities) were indispensable. A single side band identifying markers. These feral goats were obtained from radio was used to communicate with a 24-hour operator Island. They were deployed for about two weeks (Emergency Management Office) on Saipan. We could and finally removed at the end of the project. The deci- also talk directly with Macaw Helicopter’s home base. A sion to remove the radio-collared goats was made because long-range radio proved to be a beneficial requirement for it was unknown when or if a next trip to the island would logistical planning, weather updates, and emergencies. be undertaken. Boat directed Rifles A small (4.6m) boat equipped with a 12hp outboard was Two general types of rifles were used. One was the Ruger used to move materials from supply boats to shore. It also semi-automatic model mini-14 ranch rifle in .223 calibre served as a spotting platform to direct shooters onto ani- with five, 20, and 30 round magazines. The other type was mals and to land shooters at otherwise inaccessible areas the Ruger bolt action model M-77 in .220 swift calibre around the island. Typically, the small boat would depart with a four shot magazine and fitted with a 3-9 variable with an operator and a spotter. Binoculars and radios were Bushnell scope or a 6-20 variable Simmon scope and a needed. The boat would slowly move around the island bipod. CNMI law regulated the calibre of rifle used. searching for animals on the steep slopes. Once found, locations would be radioed to ground shooters who had Communications been previously deployed about the island. During these outings we would occasionally see goats close to shore in Hand-held radios were a critical link throughout the op- otherwise inaccessible areas. The small boat would nose eration, both for person-to-person and person-to-helicop- in and drop a shooter off. Again radio communications ter communications. Hand-held radios provided coordi- were of the utmost importance. Shooting from the boat nation between personnel and provided the flexibility to was also tried, but the ocean swell made this impractical adapt to any situation. It also increased our safety factor and usually ended in expended ammo with no gain.

Fig. 3 Frequency of herbs and weeds on 13 Fig. 4 Frequency of tree species found on 13 plots before and after feral ungulate eradica- plots before and after feral ungulate eradica- tion. Sarigan Island, CNMI. tion. Sarigan Island, CNMI.

136 Kessler: Eradication of goats and pigs, Sarigan Is Changes in wildlife and vegetation Wildlife

Vegetation Fruit bats’ populations appear to be stable at about 175 and showed no apparent changes. It is assumed that fruit bats are linked to the number of flowering/fruit producing The vegetation responded immediately to the removal of trees, so that any change in bat numbers would require a ungulates. The total number of plant species found in all number of years until the trees mature. Likewise there is 13 plots has increased from seven in 1997 to 17 in 1998, no apparent change in rat populations, although only a few 22 in 1999, and 25 in 2000. rats (<6/year) were ever caught. Rat trapping was done in 1999 and 2000. Many of these new species are herb and weed species (one species in 1997 vs 11 in 2000). Two species originally There were no significant changes in bird detections. There found on the plot, the fern Pteris quadriaurita and the appears to be a slight increase in the number of megapodes colonising weed Ageratum conyzoides have both declined detected from about one per station to two per station. (Fig. 3). Species found on the plots since 1998 include; Kingfisher (Halcyon chloris) populations also show a slight Blechum browneii, Calopogonium mucunoides, increase. Micronesian starling (Aplonis opaca) detections Operculina venricosa, Euphorbia hirta, Oxalis went up in 1999 but decreased in 2000. Honeyeater corniculata, Oplismenus undulatifolius, Veronica cinera, (Myzomela rubratra) detections have declined in 2000. It Emilia sp., Piper sp., and Commelina sp. These species is likely that it is too soon to see changes in these species are widespread throughout the tropics and have been ob- and the slight variations detected could be due to seasonal served in the Mariana Islands since the early 1900s (Merril foraging differences, observer variance, or to El NiÔo/La 1981). NiÔa events. Grasses and sedges have increased from one species in Catch rates for blue-tailed skinks ( caeruleocauda) 1997 to four in 2000. Tree species have increased from a and the endemic Slevin’s (Emoia slevini) have greatly total of four in 1997 to nine in 2000 (Fig. 4) and have increased (Fig. 5). shown a steady increase in the number of seedlings on the plots. These tree species are Aglaia mariannensis, DISCUSSION Artocarpus mariannensis, Cocos nucifera, Erythrina variegata, Hibiscus tiliaceus, Neisosperma oppositifolia, Eradication Trema orentalis, Premna obtusifolia, and Carica papaya. All are native species to the Marianas, except for C. pa- Goats paya, which is from the Americas but considered natural- ised (Raulerson and Rinehart 1991). The helicopter shooting worked well as a means to re- move large numbers of goats in open or steep terrain. Cal- Along with the increase in vegetation there has been an culations show that we killed 38% in approximately 21 increase in canopy cover and a decrease in ground cover hours of shooting. After this the numbers shot dropped off (from shading) on those plots near or within the forest. sharply. The goats quickly learned to recognise the sound Plots located on grasslands have shown an increase in of the helicopter. The helicopter was also useful in sur- ground cover from near zero (bare dirt) in 1997 to 100% veying remote areas for the absence of goats. cover in 2000. Line sweeps with a number of shooters was a good way to clear dense sections of forest. At first try, the line was dif- ficult to keep straight and gaps and holes would form pre- senting dangerous conditions and incomplete coverage. Once the method was practiced a number of times it be- came very efficient. Walking in a line would force the ani- mals to either try to get through or go around the top or bottom of the line. Pigs usually went through, goats went around. Spotting goats using binoculars and directing shooters to the location by radio was another method that was successful; especially in very steep terrain when the spotter could be offshore on a boat.

The “Judas goats” (Taylor and Katahira 1988) did not work for us. In reviewing the project, I believe that the failure of this operation was due to association problems between Fig. 5 Catch rates (# lizards/100 trap hours) goats already present (with established herds and ranges) for Emoia caeruleocauda and Emoia slevini and the newcomers. The collared Anatahan goats were before and after feral ungulate eradication. bigger and hairier then the small short-haired goats on Sarigan Island, CNMI. Sarigan. I suspect that over a longer period of time they

137 Turning the tide: the eradication of invasive species would have joined up, but in our short period it didn’t hap- Rifles pen. It has been proposed that the dye and flagging alone could have been the deterring factor, but this technique Except for the close-up work of hunting with pig dogs, or (using flagging) has been used since with satisfactory re- clearing caves, my choice would be to outfit every rifle sults (pers. obs.). For that project we used goats from the with a telescopic sight of at least 3x magnification. This same island (Norman Island-British Virgin Islands). It scope could be used in most situations and would greatly would have been better for us to collar Sarigan Island goats improve the accuracy of the shooter. In thick brush the (in their local ranges) immediately upon commencement scope did not appear to be a hindrance. The problem faced of operations. It is probable that some animals would have was keeping them in working order due to the hard spills been shot inadvertently, but with high visibility markings and humidity. By the end of the project we had used up all this could have been kept to a minimum. Also, if goats of our replacements (eight total). Spending money initially had been released early in the project, it is felt that they on expensive but rugged military specification (Mil. Spec.) would have joined up with survivors quicker, thus becom- scopes could mitigate this. To avoid being stuck in a situ- ing more in tune to the best hiding spots. ation where rifles can’t be used due to lack of a working scope, some rifles with iron sights should be kept on hand. Pigs Personnel The local type of snare worked well in a limited capacity. It was a low-cost method of capturing pigs. Shooting over All field personnel must be physically fit and mentally bait at night worked very well when pig concentrations prepared for hardships. Shooters should be experts in fire- were high and they were still naïve about humans. The arm use and hunting techniques. All should be motivated pig dogs, however, were the most efficient means of find- individuals picked for their ability to move over any ter- ing and killing pigs. At the time the dogs came in, we were rain under harsh conditions carrying the necessary field not killing additional pigs. They had learned to escape us equipment. A day walking through the forest is not only and it would have been difficult to kill the remaining 31 tiring but mentally nerve-racking due to the extreme ter- without the dogs. rain and constant life-threatening hazards from tripping and falling. All personnel should be familiar with the Logistics project goals and be committed to achieving them. Physi- cal and mental stresses were a constant factor in shooter Our most significant problem was the movement of con- fitness. Every effort should be made to provide comforts sumable supplies such as water, gas, and food to the is- in camp to allow shooters to relax. This could include: land. This used up much of our budget in the form of good chairs/recliners to rest sore muscles; a full time cook; helicopter time. Local fishing boats were cost-efficient, and cold drinks. These amenities go a long way to keep- but hard to schedule and were weather-dependent. Food ing an isolated crew, working under harsh conditions, fo- was not as big a problem as drinking water and gasoline. cused on the project. We did have rainwater catchments established, but it rained little during the project’s duration. Vegetation and wildlife

Supply procurement and coordination by the project su- Vegetation pervisor was an added burden that detracted from smooth running field operations. It is recommended in the future In the Marianas, it seems that goats and pigs are a destruc- that a supply officer be set-up that is intimately familiar tive force capable of changing the microclimate of the for- with the needs of the island crew. This person’s sole re- est floor. The destruction of the ground cover, the drying sponsibility would be to plan, purchase and ship supplies out of the forest floor, and the subsequent loss of soil to the island. through erosion kills the trees. The eating of new growth Equipment by ungulates suppresses any regeneration capabilities of the forest. The result is a steady decline of forest habitat whether it is native or coconut forest. This in turn has All equipment should be first rate with plenty of spares on serious implications for native wildlife that require forest. hand. Much gear will be damaged and should be replaced immediately to keep the shooters motivated and avoid Removal of ungulates has stopped and reversed the proc- dangerous situations; plan supply and shipping alternatives ess of forest loss and has re-established the forest floor well before-hand and have alternate sources on standby. microclimate (in less than a year). Likewise, the native One item that I found to be of importance was military forest is expanding and regenerating. Many new trees were MRE’s or Meals Ready to Eat. One of these each day for observed growing in areas that were previously grassland; lunch allowed shooters to stay in the field and consider- the sudden eruption of new growth has undoubtedly slowed ably boosted morale. erosion and contributes to new soil being laid down.

The general trend appears to be the changing of grassland to forest. Areas of Chrysopogon acicularis grassland and

138 Kessler: Eradication of goats and pigs, Sarigan Is bare dirt are sprouting new thickets of the shrubby species monitoring to see if populations change. Although no defi- Dodonaea viscosa. In some areas of the Miscanthus grass- nite increase can be stated now, fruit bats have been ob- land new stands of Morinda citrifolia, Tremna orientalis, served roosting in young Tremna trees that had previously and Leucaena leucocephala (introduced species) trees have been Miscanthus grassland. This expansion in roosting become established. Some of this growth in the Miscanthus and foraging habitat can only be viewed as beneficial. could be a result of the combination of burning and ungu- late removal. Rat populations have shown no increase although the data is cursory. On the neighbouring island of (no fe- The unknown side to this increase in vegetation is the ex- ral animals), the Pacific rat is extremely common and can plosion of the invasive vine Operculina ventricosa. This be seen throughout the day (pers. obs.). On Sarigan (since vine, which I had not observed prior to ungulate removal, 1996), rats were uncommon (rarely seen only at night); now covers most of the native forest and surrounding only a few were caught during surveys although this could Chrysopogon acicularis grassland in the central valley. It be a function of trap placement and/or bait. It is specu- had been previously recorded as present on Sarigan lated that feral cats and monitor lizards play a role in the (Fosberg 1979), but is a species that is readily consumed reduced rat numbers on Sarigan. It remains to be seen what by goats. It is unknown what effect this vine is having on an increase in fruit will have on the rat population and the regeneration of the native forest. The vine does not consequently the cat and bird populations. appear to do well in the coconut forest or Miscanthus grass- land. Although it blankets the central valley, new tree sap- One species that must be mentioned is the dog dung fly lings are still pushing up through the vine. On a more Musca sorbens. Unfortunately no scientific insect data of positive thought, it has acted as a band-aid on the heavily any kind was collected and the evidence on this species is disturbed areas, shading the ground and trapping mois- anecdotal. This species is considered a pest and had pre- ture. It seems to provide an increase in foraging habitat viously occurred in high numbers on Sarigan (pers. obs.). for lizards, and megapodes have been observed to use it Food had to be covered. On the last follow-up trip almost as well. Only time and continued monitoring will reveal no flies were encountered (<5) and food could be left un- its impact. An observation of note on the vine, was clus- covered. This species requires animal dung for its life ters of leaf-footed or squash bugs (Family Coreidae) ap- cycle, and the apparent reduction in numbers is probably parently feeding on it. Whether this species will act as a linked to the elimination of ungulates. Removing this spe- form of biological control remains to be seen. cies has important social-political implications for future projects in the Marianas and could be touted as a major Wildlife benefit. Also, this species was observed to be a prey item for skinks. With an apparent decrease in flies and an in- The most rapid change of any wildlife species is the in- crease in skinks, one wonders what might be filling the crease of skinks, mostly due to their high reproductive rate. skinks’ needs. Insect data needs to be collected for future The combination of an enlargement in forage area (in- projects. creased vegetation) and the removal of a direct predator (the pig) has seemingly benefited these lizards. Although the removal of feral goats and pigs has had some unforeseen consequences, the majority of the changes can The skinks themselves form a prey base, especially for only be viewed as positive. The project goals of stopping kingfishers and megapodes. Indeed there seems to be an forest loss and increasing megapode (and fruit bat) habitat upward trend in these two bird species numbers, however appears to have been achieved. This island serves as an it is probably too soon to tell. Unfortunately, these skinks important ongoing experiment in island wildlife manage- probably function as a prey item for monitor lizards ment. (Varanus indicus - believed by some to be introduced) and feral cats, which also prey on the native birds. It is inter- Future needs esting to speculate what affect an increase in these two species’ populations will have on Sarigan. Probably every eradication project could use more fund- ing and professional help in documenting the changes. Noticeable increases in bird populations, especially those Removal of herbivores affects all aspects of an island’s that depend on mature tree species, will require a longer ecosystem and creates a large-scale laboratory for study- monitoring period. But it is probable that the increases ing these changes. More complete surveys of the plant seen in major food species such as the coral tree (Erythrina and wildlife communities of Sarigan and of neighbouring variegata) and papaya (Carica papaya) will be benefi- islands need to be undertaken to provide basic knowledge cial. Papaya had not been evident in the forest prior to of the native species and their life histories. These surveys eradication and now is abundant (a primary starling and should be performed a minimum of twice a year to repre- fruit bat food). Coral trees, which produce a beautiful red sent both the dry and wet seasons. Surveys must be stand- flower, are now observed as a common sapling established ardised and be of a simple design so as to be readily repro- in the Chrysopogon grasslands. This is the primary source ducible. Data acquired needs to be organised and published of food for honeyeaters and fruit bats during the dry sea- for future biologists. sons (December-April). Bat numbers will require further

139 Turning the tide: the eradication of invasive species

One of the missed opportunities of this project was to study Fosberg, F. R.; Sachet, M. H. and Oliver, R. 1979. A geo- changes in the nearshore marine community and its rela- graphical checklist of the Micronesian Dicotyledonae. tion to feral ungulates and forest destruction. If another Micronesica. 15: (1-2). such programme is undertaken in the Marianas, it is urged that some marine transects be established to explore these Merrill, E. D. 1981. Plant life of the Pacific world. Charles relationships. E. Tuttle Co. Rutland, Vt.

It is my opinion that the two most important aspects to Morton, J. M.; Lusk, M.; Hughs, G. and Wiles, G. 2000. achieving a complete eradication on Sarigan was momen- Occurrence and density of avifauna and Mariana fruit tum and communications. Momentum must be maintained bats on Sarigan, Commonwealth of the Northern once a project is started or the result will only be wasted Mariana Islands, in July 1999. Unpublished report by time and effort. Few enjoy slaughtering the animals, and US Fish & Wildlife Service, Honolulu Hawaii. to do so to only have a project halted midway is lamenta- ble. Two major considerations in sustaining momentum Obha, T. 1994. Flora and vegetation of the Northern are politics and supplies. Without good support for either Mariana Islands. Natural History Research, Special the project is questionable. The other major factor for us issue number 1. Natural History Museum and insti- was communications in the field. Without effective and tute, Chiba. Japan. efficient ways to coordinate shooters we could not have achieved what we did in so short a period. Raulerson, L. and Rinehart, A. 1991. Trees and shrubs of the Northern Mariana Islands. Publisher; Coastal Re- ACKNOWLEDGMENTS sources Management, Office of the Governor, Saipan, CNMI. The initial concept was supported by the late B. Harper of the USFWS-Honolulu without whose vision and backing Taylor, D. and Katahira, L. 1988. Radio telemetry as an this project could not have been undertaken. Thanks also aid in eradicating remnant feral goats. Wildlife Society to Lynn Raulerson of University of for outlining the Bulletin 16: 297-299. methods of vegetation sampling and having the patience to identify all the various plant samples. Many people Worthington, D. J.; Marshall, A. P.; Wiles, G. J. and from different organisations helped to make this project a Kessler, C. C. 2001. Abundance and management of reality, these include the U.S. Navy-COMNAVMAR, Cap- Mariana fruit bats and feral ungulates on Anatahan, tain and crew of the USS Niagara Falls and HC-5, CNMI- Mariana Islands. Pacific Conservation Biology, 7: DFW and CNMI Dept. of Natural Resources, Office of 134-142. the Mayor of the Northern Islands, and USGS-BRD. Two of the more involved personnel who where not mentioned in the text include A. Marshall past supervisor of CNMI- DFW, and T. Sutterfield biologist USN-Pearl Harbor. Per- sonnel who risked injury during field operations include: E. Santos, J. Manygoats, L. Ragamar, J. Omar, D. Holton, and M. Severson. Special mention must be made of T. McCay and H. Gideon both who spent the continuous 60 days on Sarigan; such dedication is noteworthy. V. Camacho of CNMI-DFW helped with surveys and han- dled much of the logistics. Thank you to T. Thiemer and J. Ganey for providing comments on the draft manuscript. Thank you also to the reviewers B. Coblentz and J. Parkes for their suggestions on changes to be incorporated into the final draft. REFERENCES

Fancy, S. G.; Craig, R. J.and Kessler, C. C. 1999. Forest bird and fruit bat populations on Sarigan, Mariana Is- lands. Micronesica 31(2): 247-254

Fritz, G. 1902. Reise nach den nordlichen Marianen. Mitteilugen von Forschungsreisenden und Gelehrten aus den Deutschen Schutzgebieten 15: 96-118.

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