Management and Conservation Article

Bio-Economics of Large-Scale Eradication of Feral GoatsFrom Santiago Island, Galapagos

FELIPE CRUZ, Galapagos National Park Service, Puerto Ayora, Isla Santa Cruz, Galapagos, Ecuador, and Charles Darwin Foundation, Casilla 17-01-3891 Quito, Ecuador

VICTOR CARRION, Galapagos National Park Service, Puerto Ayora, Isla Santa Cruz, Galapagos, Ecuador

KARL J. CAMPBELL,1 Galapagos National Park Service, Puerto Ayora, Isla Santa Cruz, Galapagos, Ecuador, and Charles Darwin Foundation, Casilla17-01-3891 Quito, Ecuador; School of Natural and Rural Systems Management, University of Queensland, Gatton, Queensland 4343, Australia

CHRISTIAN LAVOIE,2 Galapagos National Park Service, Puerto Ayora, Isla Santa Cruz, Galapagos, Ecuador, and Charles Darwin Foundation, Casilla17-01-3891 Quito, Ecuador; United Nations Development Program, Avenida Amazonas 2889, Quito, Ecuador

C. JOSH DONLAN,3 Advanced Conservation Strategies, P.O. Box 1201, Midway, UT 84049, USA, and Department of Ecology and EvolutionaryBiology, Cornell University, Ithaca, NY 14853-2701, USA

ABSTRACT Invasive mammals are premier drivers of extinction and ecosystem change, particularly on islands. In the 1960s, conservation

practitioners started developing techniques to eradicate invasive mammal populations from islands. Larger and more biologically complex

islands are being targeted for restoration worldwide. We conducted a feral goat (Capra hircus) eradication campaign on Santiago Island in the

Galapagos archipelago, which was an unprecedented advance in the ability to reverse biodiversity impacts by invasive species. We removed

.79,000 goats from Santiago Island (58,465 ha) in ,4.5 years, at an approximate cost of US$6.1 million. An eradication ethic combined with a

suite of techniques and technologies made eradication possible. A field-based Geographic Information System facilitated an adaptive

management strategy, including adjustment and integration of hunting methods. Specialized ground hunting techniques with dogs removed

most of the goat population. Aerial hunting by helicopter and Judas goat techniques were also critical. Mata Hari goats, sterilized female Judas

goats induced into a long-term estrus, removed males from the remnant feral population at an elevated rate, which likely decreased the length

and cost of the eradication campaign. The last 1,000 goats cost US$2.0 million to remove; we spent an additional US$467,064 on monitoring to

confirm eradication. Aerial hunting is cost-effective even in countries where labor is inexpensive. Local sociopolitical environments and best

practices emerging from large-scale, fast-paced eradications should drive future strategies. For nonnative ungulate eradications, island size is

arguably no longer the limiting factor. Future challenges will involve removing invasive mammals from large inhabited islands while increasing

cost-effectiveness of removing low-density populations and confirming eradication. Those challenges will require leveraging technology and

applying theory from other disciplines, along with conservation practitioners working alongside sociologists and educators. ( JOURNAL OF

WILDLIFE MANAGEMENT 73(2):191–200; 2009)

DOI: 10.2193/2007-551

KEY WORDS bio-economics, Capra hircus, eradication, Galapagos, invasive mammals, island conservation, Judas goats,nonnative mammals, restoration.

Islands are a small percentage of the Earth’s total area, yet

they harbor a large percentage of biodiversity, including

many threatened and endangered species (Aguirre-Munoz

et al. 2008). Islands have also suffered the greatest number

of vertebrate extinctions (Martin and Steadman 1999,

Groombridge and Jenkins 2002). Nonnative mammals are

overwhelmingly the major driver of biodiversity loss and

ecosystem degradation on islands. Nonnative predators,

such as rats (Rattus spp.) and cats (Felis silvestris catus), have

decimated endemic rodent, reptile, and avian populations

and have extirpated seabird colonies on islands around the

globe (Nogales et al. 2004, Towns et al. 2006). Feral pigs

(Sus scrofa) feed on island plants, prey on insular vertebrates,

and raid nests (Coblentz and Baber 1987, Choquenot et al.

1996). Nonnative herbivores, such as goats (Capra hircus),

have caused wholesale changes on insular plant commun-

ities, as well as secondary impacts via habitat degradation

(Coblentz 1978, Ebenhard 1988, Donlan et al. 2002,

Campbell and Donlan 2005).

Over the past 3 decades, nonnative mammal eradication

from islands has become one of society’s most powerful toolsfor preventing extinction and restoring ecosystems (Veitch

and Clout 2002, Donlan and Wilcox 2008). Rodents, goats,

and cats have been successfully removed from .330, 128,

and 74 islands worldwide, respectively (Nogales et al. 2004,Campbell and Donlan 2005, Howald et al. 2007, Donlan

and Wilcox 2008). Rodents, goats, and cats are now being

removed from larger islands at a faster rate than ever before

(Algar and Burrows 2004, Cruz et al. 2005, Phillips et al.2005, Howald et al. 2007, Morrison et al. 2007).

We report on the successful eradication of goats from

Santiago Island, Galapagos Islands, Ecuador, which was

part of Project Isabela, the world’s largest invasive mammaleradication effort. The Santiago Island eradication cam-

paign, the largest ever attempted in terms of island size

(58,465 ha) and number of animals removed, was mountedas an opportunistic capacity-building exercise (e.g., hunting

training and technique development) leading up to goat

eradication on Isabela Island (458,812 ha). Both campaigns

followed the eradication of goats from Pinta Island (5,940

1 Present Address: Island Conservation, 100 Shaffer Road, SantaCruz, CA 95060, USA2 Present Address: Conservation International, 2011 Crystal Drive,Suite 500, Arlington, VA 22202, USA3 E-mail: jdonlan@advancedconservation.org

Cruz et al. � Eradication in the Galapagos Islands 191

ha) and pigs from Santiago Island (Campbell et al. 2004,Cruz et al. 2005). Part of an archipelago-wide invasivespecies initiative, a goal of the Santiago Island goateradication campaign was to develop models, techniques,and technologies necessary to cost-effectively eradicateinvasive mammals from large islands. Given that invasivemammals occupy most islands globally and a largepercentage of species threatened with extinction are insular(Atkinson 1985, Aguirre-Munoz et al. 2008), replicating

large-scale nonnative mammal-eradication campaigns isvital for biodiversity conservation.

STUDY AREA

Located in the center of the Galapagos archipelago,Santiago Island enjoyed protected status and received littlevisitation by scientists and tourists (Fig. 1). A major volcano(907 m) was in the northwest part of the Island; therefore, alarge portion of the island was basaltic lava (approx. 30%).Five endemic reptiles and .20 endemic birds were presenton the island. Santiago Island held 113 plant speciesendemic to the Galapagos archipelago, 6 of which wererestricted to the island. Herbivory by goats and donkeys(Equus asinus) was the main threatening process to most ofthe island’s threatened plants (Tye 2000, Tye and Jager2000). Goats likely caused the extinction of the SantiagoIsland endemic Blutaparon rigidum, which was last seen in1906. Massive herbivory by goats, donkeys, and pigs haltedrecruitment of trees, cacti, and forbs across the entire island.Grasslands replaced highland forests because of nonnativeherbivory (Fig. 2; Schofield 1989, Hamann 1993). Predationby pigs and habitat degradation by goats had secondaryimpacts on wildlife as well, including population declines ofGalapagos rails (Laterallus spilonotus) and giant tortoises(Geochelone elephantopus; MacFarland et al. 1974, Donlan etal. 2007).

In 1813, goats were accidentally introduced to SantiagoIsland, but the initial introduction likely failed (Porter 1815,Cookson 1875, Darwin 1906). Goats were successfullyintroduced during settlement attempts between the 1920sand 1940s. The goat population was estimated at 80,000 to100,000 in the 1970s and 1980s (Calvopina and de Vries1975, Stone et al. 1988). From 1968 to 1982, goats,donkeys, and pigs were hunted under a control programwith an emphasis on pigs. During control programs and thepig eradication campaign (1992–2001), �19,167 goats wereremoved.

METHODS

Ground Hunting Phase: December 2001 to January 2004We initiated the goat eradication campaign immediatelyfollowing pig removal; the large goat population keptvegetation open, facilitating effective pig hunting (Cruz etal. 2005). We eradicated donkeys from Santiago Islandconcurrently with the goat eradication campaign (Carrion etal. 2007). We adopted 4 ground-hunting methods andrefined them during the eradication: 1) corrals, 2) freehunting (with and without dogs), 3) a form of team line-hunting termed rastrillo, and 4) strategic spot huntingfacilitated by helicopters for transport (Fig. 3).

For ground hunting, we divided the island into 21 zonescomprising of 137 blocks (Fig. 1B; Lavoie et al. 2007).Zones averaged 2,060 ha (414–4,491 ha), and blocksaveraged 323 ha (50–896 ha). We based zone size on anarea that could be systematically hunted by a hunting teamin rastrillo in one trip (approx. 15 days), thus size varieddepending on vegetation, topography, and relative initial

Figure 1. (A) The Galapagos Islands, Ecuador. (B) Santiago Island withground hunting blocks and subblocks, along with established trail systems.(C) Aerial hunting blocks and Spot-imaging used to highlight volcanic andvegetated areas of the island. (D) Judas goat blocks, generated as Thiessenpolygons from equidistant points, and a vegetation classification generatedfrom Spot imaging, which aided the design of experiments to assess theefficiency of different types of Judas Goats. Island blocks were usedthroughout the entire goat eradication campaign (Dec 2001 to Mar 2006).

192 The Journal of Wildlife Management � 73(2)

animal densities (Lavoie et al. 2007). We divided zones intoblocks; we based boundaries on topography, trails, and huts.Trail and hut networks constructed during the pigeradication campaign facilitated goat eradication, as did anintimate knowledge of the island by hunters.

Our ground-hunting teams varied in size from 32 to 55and consisted of locals, many of whom had no previoushunting experience. We trained hunters in all facets ofhunting and field skills, including dog handling, GlobalPositioning Systems (GPS), radios, rifles, first aid, andtelemetry. Ground hunters used 0.223 caliber rifles (Ruger,Southport, CT) and 55-grain, pointed, soft-point ammu-nition (Winchester, East Alton, IL). Every hunter carried aGPS unit and recorded their daily movements. Hunters alsorecorded a variety of spatial and nonspatial data, includingkills, escapes, sex, location, and area traveled (Lavoie et al.

2007). Hunters collected tails to confirm reported kills,except when a hunter shot .80 animals/day, and tailcollection decreased hunting efficiency.

During the first 2 years of the campaign, we corralledgoats in the highlands where they concentrated during drymonths (Fig. 3). We constructed temporary corrals withwinged extensions of netting (10 3 10-cm mesh) strungbetween trees or posts at an average of 1.8 m high, with askirt hanging on the ground weighted down with rocks. Weused winged extensions, up to 6.5 km long, to funnelanimals into corrals. Goats were mustered into corrals byhunters on foot or horseback, along with the aid of air hornsand rifle shots. We euthanized corralled goats in accordancewith American Association of Zoo Veterinarians guidelines(Miller et al. 2006).

Free hunting took place with and without dogs. The first

Figure 2. Impact of nonnative herbivory and recovery of highland habitat following goat eradication on Santiago Island, Galapagos, Ecuador. (A) Anexclosure and surrounding area in the highlands of Santiago Island in March 1999 and (B) March 2005.

Figure 3. Timeline of the methods we used during the goat eradication campaign on Santiago Island, Galapagos, Ecuador (Dec 2001 to Mar 2006). The topbar delineates phases of the campaign. We used methods consecutively and sequentially. We reconfirmed eradication in January 2007 and December 2007.

Cruz et al. � Eradication in the Galapagos Islands 193

free-hunting phase took place from December 2001 toOctober 2002. The hunting team would cover an entirezone during a trip, breaking into groups of 1–3 hunters and0–6 dogs and covering a block or subset of a block during aday. Radio contact between groups facilitated full coverageof the area. Up to 100 hunting dogs accompanied free-hunting teams; we used 2 dog types: New Zealandhuntaways and descendants of Labrador–German shepherdcrosses. Hunters typically worked with 2 dogs each. All dogsunderwent intense training, and we removed those notmeeting set standards. Dogs were short-ranging, couldfollow ground scents for �300 m, and could effectivelyfollow wind scents. We conducted aversion training withelectric shock collars (Tri-tronics, Tucson, AZ) whennecessary to produce goat-specific dogs and eliminate risksto native wildlife. All dogs wore radiotelemetry collars(Sirtrack, Havelock North, New Zealand).

In August 2002, we switched the primary ground-huntingstrategy to rastrillo, a line-hunting technique adopted fromisland conservation practitioners in New Zealand (Parkes etal. 2002; N. Macdonald, ProHunt New Zealand Ltd,unpublished data). Rastrillo involves a hunting team work-ing at fixed spacing (100–150 m) and systematically movingthrough an area, typically proceeding into, or perpendicularto, the prevailing wind. Hunters maintain their place in theline by radio communications, hand-held GPS units, and apriori fixed points (Lavoie et al. 2007). From August 2002to October 2003, 2 hunting teams, averaging 15 hunterseach, systematically hunted all blocks. A near permanentpresence was maintained on the island by rotating teamsevery 15 days. Zones and blocks were hunted with the goalof minimizing escapes and keeping any escaping goats aheadof a rolling front, putting them at risk in the next block orzone hunted. All zones were hunted �3 times. FromJanuary to October 2003, ground-hunting effort concen-trated in areas of thickest vegetation (5,684 ha) andsurrounding areas (6,012 ha) as a buffer to immigration(Fig. 1C). Blocks in the lowland areas, with open vegetation,were left for the aerial hunting campaign.

In October 2003, we altered ground-hunting methods toincrease efficiency and boost hunter morale. Kill rates forgroups hunting in rastrillo were low, and competitionbetween hunters was nonexistent. Hunter morale was low,and goats were moving out of hunting zones because ofincreased hunting activity. Consequently, ground huntersswitched back to free hunting. Kill rates increased,competition between hunters increased, and goats movingfrom one zone were put at risk from hunters in neighboringzones. We used a mix of free hunting and rastrillo fromOctober 2003 until the end of campaign (Fig. 3).

Aerial Hunting Phase: February 2004 to May 2004Because of delays with importation and licensing ofhelicopters and their crews, we initiated aerial hunting latein the campaign (Fig. 3). The aerial component consisted of2 helicopters (McDonnell Douglas MD500D/E, Boeing,Chicago, IL) with pilots and shooters highly experienced inaerial hunting. We used 2, sometimes 3, shooters per

helicopter. Aerial shooters used semiautomatic 12 gaugeshotguns (M1 Super 90; Benelli, Urbino, Italy) andsemiautomatic 0.223 caliber AR15 rifles (JP15; JP Enter-prises, Hugo, MN). Shooters tracked the number of animalsshot with manual counters, and the pilot recorded thelocation and relative numbers shot with a GPS.

We partitioned Santiago Island into 10 blocks for aerialhunting, ranging from 3,547 ha to 10,109 ha (Fig. 1C;Lavoie et al. 2007). We determined block size primarily byopenness of vegetation, relative goat density, and helicopterflight times, which were limited to 2 hours. We uploadedhunting blocks to GPS units to delineate block boundaries,and we recorded helicopter tracks at 20-second intervals(Lavoie et al. 2007). We hunted each zone systematicallyand hunted zones closest to base camp first to minimizeeducating goats to helicopters. Once the kill rate dropped to,30 goats/hour, we combined zones. Minimizing escapeswhile aerial hunting was the priority. Goats quickly becameeducated and wary, often hiding in bushes, caves, or lavatunnels. Aerial shooters were often dropped off to huntgoats that were in refuges. Toward the end of the aerialhunting campaign and before releasing Judas goats (seebelow), the entire island was hunted several times consec-utively with 1–3 weeks between each episode.

Judas Goat Phase: June 2004 to November 2005Judas goats (JGs) are goats captured, fitted with radio-telemetry collars, and released (Taylor and Katahira 1988).Because goats are gregarious, JGs search out and associatewith other goats (Rainbolt and Coblentz 1999). Judas goatscan be monitored and any associated feral goats killed(Taylor and Katahira 1988, Rainbolt and Coblentz 1999).We captured goats for JGs from nearby Isabela Island,where we mustered them into corrals by helicopter orcaptured them with the aid of helicopter. We quarantinedand ear-tagged goats. We then sterilized female and maleJGs and terminated JG pregnancies (Campbell et al. 2005).

We conducted a field experiment to assess the efficacy of 3types of JGs: males, females, and females with hormoneimplants; the latter coined Mata Hari goats (Campbell2007, Campbell et al. 2007). Using dentition patterns(Mitchell 1982), we blocked all goats by age, and werandomly assigned females between the 2 treatments. Weadministered Compudose-100 silicon rubber implants tohormone-treated females to induce a prolonged estrus effect(21.1 mg estradiol 17b; Elanco, West Ryde, Australia;Campbell et al. 2007). We fitted JGs with telemetry collars(Sirtrack, Havelock North, New Zealand) and deployedthem by helicopter in 2 batches: June 2004 (n ¼ 123) andNovember 2004 (n ¼ 90). We deployed JGs at 2.25-kmequidistant points in all areas where goats had beenpreviously shot. In lava fields, where goats had never beenshot, we deployed JGs at 2.7-km equidistant intervals (Fig.1D). In both deployments, we randomly allocated JGs fromeach group into 5 vegetation types, except in the firstdeployment, where we deployed males solely in lava (Lavoieet al. 2007). However, those male goats quickly moved tovegetated areas after being released (K. Campbell, Island

194 The Journal of Wildlife Management � 73(2)

Conservation, unpublished data). We used multinomiallogistic regression models to assess differences in associationof feral goats between the 3 types of JGs. We used SPSS(SPSS 16; SPSS, Chicago, IL) for all statistical analyses andadopted an a-level of 0.05.

Because of helicopter operational problems, groundhunters with dogs monitored JGs between July 2004 toFebruary 2005. Hunters worked in pairs; one hunter trackedJGs with a TR4 telemetry receiver (Telonics, Mesa, AZ)and a 3 element Yagi antenna (Sirtrack), whereas the otherwas free to shoot associated goats. Hunters leashed dogs inopen country and released them to search freely for goatsigns in thicker vegetation. Judas goats associated withanother JG were shot to maintain searching behavior.

After February 2005, JGs were monitored by helicopter.We captured JGs associated with other JGs and redeployedthem in vacant areas; we constantly updated those areas withmaps containing the last monitored position for each JG.We collected DNA samples from Santiago Island and fromthe remaining goat populations in the archipelago. If goatsare found in the future, it may be possible to determinewhether they were introduced from another island or arelocal goats that evaded eradication efforts (Abdelkrim et al.2007).

Confirmation and Monitoring: November 2005 toJanuary 2007In November 2005, we removed all JGs from the island toallow ground hunters with dogs to monitor for goat signs(e.g., footprints, scat, bedding sites) and scent trails withoutconfusing JGs with feral goats. Few, if any, feral goats werebelieved to remain. Immediately after removing JGs,hunters with dogs and helicopter support conducted 2complete sweeps of the island. We also conducted additionalmonitoring trips between September 2006 and January2007.

We tracked all costs and effort associated with theeradication campaign. We calculated cost per effort foreach activity (e.g., $/dog-hr, $/helicopter-hr), incorporatingsalary, administration (including institutional overhead),management, and logistical costs. We assigned the percen-tages of time or resource use of each cost to the 4 principalmethods: helicopters, hunters, dogs, and JGs. We convertedall costs to 2007 United States dollars unless notedotherwise. Some existing infrastructure was already in placeon the island (i.e., trails, huts) and was not included in ourreported costs. Those costs comprised a small fraction of theoverall eradication campaign expenditures.

RESULTS

From onset to confirmation, our eradication campaign lasted52 months (Figs. 3, 4), and we removed 79,579 goats.Ground hunting and corrals removed 84% of the goats(Table 1). Once helicopters were available (Feb 2004), theywere effective in reducing the remaining goat population(Table 1; Fig. 5). Judas goats facilitated removal of the finalanimals, and ground hunters with dogs were critical in

detecting and removing the last animals. Total cost of the

eradication campaign was US$6,164,394.

Ground Hunting Phase: December 2001 to January 2004

Corrals were cost-effective in the beginning of the

campaign, removing 12,431 goats at an average cost of

US$24 per goat (Table 1; Fig. 5). Early in the eradication

campaign, we relied on free hunting to maximize kills;

hunters could concentrate on areas frequented by goats.

Rastrillo was often an effective hunting method; it became

less effective when 1) we used new hunters without hunting

skills, or 2) experienced hunters lost motivation from having

to follow set routes that resulted in less kills than if they

were free hunting. When those conditions arose, we

resorted to free-hunting methods, which trained hunters,

increased morale and kills, and allowed hunting teams to

cover several zones simultaneously.

Aerial Hunting Phase: February 2004 to May 2004

We removed .12,000 goats from Santiago Island with

aerial hunting, most within the first 4 months of helicopter

operations (12,060 goats shot/262 hr of flying; Fig. 5). Early

in the campaign, 2 shooters per helicopter, which increased

the aircraft’s agility, were most effective. Later, when goat

Figure 4. Goat kills and hunting effort during the Santiago Islanderadication campaign, Galapagos, Ecuador (Dec 2001 to Nov 2005). A)Goats killed using all techniques (solid line) and cost per goat (dashed line).We did not adjust costs for inflation. B) Total hunting effort (hr) for eachmethod. Judas goat checks include helicopter and hunter hours.

Cruz et al. � Eradication in the Galapagos Islands 195

densities were reduced, 3 shooters per helicopter were

effective because it increased the ability to locate goats.

Judas Goat Phase: June 2004 to November 2005

Total effort during the JG phase consisted of 4,989 ground-

hunter hours, 7,720 dog hours, and 230 helicopter hours

(Table 1; Figs. 4, 5). We killed 617 goats associated with

JGs (319 aerial and 298 ground checks). We killed an

additional 557 nonassociated goats during JG operations (97

aerial and 460 ground checks). We recaptured JGs, trans-

located them, and redeployed them 1,429 times by

helicopter. Checking JGs and shooting associated animalsby helicopter was more cost-effective than checking byground (US$759/goat vs. US$1,590/goat). However, whenwe include both associated and nonassociated goats, cost-effectiveness of checking JGs by helicopter or ground wascomparable (US$582/goat vs. US$625/goat).

We removed the final 1,000 goats between July 2004 toNovember 2005 (17 months). Ground hunters with dogsremoved 191 (19% of the last 982 goats) goats before May2005. Aerial hunting removed 36 (4%) of the remaininggoats, and JG operations removed 732 (75%) goats, withthe last associated goat removed in August 2005. Groundhunters using the rastrillo method, with helicopter support,removed the last 23 goats (2%).

Averaged over the entire JG campaign, Mata Hari JGsperformed approximately 1.5 times better in attracting maleferal goats than other females or males (Fig. 6). Controllingfor time since the start of JG phase (P , 0.001 for allmodels), association of feral males differed among the 3 JGstypes (log-likelihood v2 ¼ 8.04, P ¼ 0.01, nfemale ¼ 206,nMataHari ¼ 230, nmale ¼ 98). There were no differencesbetween the JGs with regard to association of feral femalesand all goats (F: log-likelihood v2 ¼ 0.414, P ¼ 0.81; allgoats: log-likelihood v2¼ 0.663, P¼ 0.72). The sex ratio ofnonassociated goats killed during the JG phase was less

Table 1. Goats killed, effort, and costs associated with each hunting method during the goat eradication campaign on Santiago Island, Galapagos, Ecuador(Dec 2001 to Nov 2005). Ground hunting costs include hunting dog expenses. Ground hunting and Judas goat operations include monitoring efforts (Dec2005 to Jan 2007). All costs are in 2007 United States dollars.

Parameters Ground hunting Corrals Aerial hunting Judas goats Total

No. of goats killed 53,782 12,431 12,192 1,174 79,579Effort (hr) 60,042 5,516 288 5,219a 71,060Total cost (% of total) 4,576,244 (74) 300,907 (5) 413,259 (7) 873,983 (14) 6,164,394Average cost/goat 85 24 34 744 77Average cost/ha 105

a Includes hr checking for Judas goats by helicopter (n ¼ 230) and on ground (n¼ 4,989).

Figure 5. Goats killed and cost per goat for each hunting method duringthe Santiago Island goat eradication, Galapagos, Ecuador (Dec 2001 to Nov2005). A) Goats killed (solid line) and cost per goat (dashed line) usingground-hunting methods (free hunting and rastrillo, and goats killed (�)and cost per goat (*) using corrals. B) Goats killed (black solid line) andcost per goat (black dashed line) using aerial hunting, and goats killed (greysolid line) and cost per goat (grey dashed line) using Judas goats. Cost dataappear on a log scale, not adjusted for inflation.

Figure 6. Mean probability of association (95% CI) of male, female, andMata Hari female Judas goats (JG) on Santiago Island, Galapagos,Ecuador, between June 2004 and November 2005. We restricted data tosingle JGs located with feral goats. When we use the time since the start ofthe JG campaign as a covariate, Mata Hari JGs perform significantly betterthan female and male JGs at associating with feral males. We pooledmultiple association events of individual JGs across JGs of that type. Samplesizes: Mata Hari ¼ 230, females¼ 206, males¼ 98.

196 The Journal of Wildlife Management � 73(2)

skewed toward females than goats associated with JGs,suggesting that JGs were successful in removing males fromthe feral population early on in the JG phase (Fig. 7).

Monitoring and Confirmation: November 2005 toJanuary 2007After the last goat was shot in November 2005, we invested103 helicopter hours, 3,990 ground hunter hours, and 5,805dog hours in confirming eradication, which represented 8%of the costs for the entire campaign (US$467,064). Movinghunters daily by helicopter increased ground-hunter hourlycost from US$47 to US$72 but allowed the island to becovered in ,2 months rather than .6 months. Followingconfirmation, we redeployed 20 JGs back onto the island toassist future monitoring efforts for detecting possible goatreintroductions.

In January–December 2007, we reconfirmed eradication ata cost of US$173,717. Between September 2006 andJanuary 2007, we covered the entire island again with teamsof ground hunters and dogs. In December 2007, we checkedJGs by helicopter: 3 JGs were dead, one was not located, andall others were either alone or associated with other JGs.Total monitoring cost, including reconfirmation, wasUS$640,781 (10% of campaign cost).

DISCUSSION

Successful removal of goats from Santiago Island demon-strated that, if sufficient funds are available, large-scale andswift goat eradications are technically feasible. The SantiagoIsland campaign was the world’s largest invasive mammaleradication undertaken, in terms of numbers of animalsremoved and island size (Campbell and Donlan 2005). Incomparison, 29,000 animals were removed from SanClemente Island, California, USA (14,800 ha, approx.0.25 the size of Santiago Island) during a campaign thatspanned .2 decades (Keegan et al. 1994). On Pinta (5,940ha) and Raoul (2,943 ha) islands, .41,000 and 10,000 goatswere removed, respectively, during a period of 20–30 years(Parkes 1990, Campbell et al. 2004).

A lesson that emerged from our work was the importanceof an eradication ethic (Morrison et al. 2007). A goal ofcomplete removal dictates much of the strategy of aneradication campaign, which differs substantially fromcontrol efforts, where a portion of the population isharvested and escape rates are of little concern. Minimizingepisodes when an animal escapes a hunting event is essentialduring an eradication campaign to prevent a naıvepopulation from learning to avoid hunting methods (Parkes1990, Morrison et al. 2007). Because animals at lowdensities can be difficult to detect (Russell et al. 2005),educated animals increase costs and the probability oferadication failure. From an operational perspective, large-scale eradications present a paradox: hunters characteristi-cally prefer working alone with the single focus of killing acertain number of animals in a certain period of time and aregenerally less concerned with animals that evade theirmethods. For large-scale eradications to succeed andmaximize the conservation return on investment, an

eradication ethic is essential. Every animal, from the firstto the last, must be treated as the last animal on the island.The campaign must embrace a zero-escape policy.

A blend of local and international expertise, along withcapacity building throughout the campaign, contributed tothe success of the Santiago Island eradication. The projectwas a bi-institutional project of the Galapagos NationalPark and the Charles Darwin Foundation. A manager fromeach institution comanaged all aspects of the campaign; bothmanagers were Galapagos natives. A nonlocal managercoordinated field operations, including technical strategies.A Geographic Information System (GIS) technician waspresent in the field throughout the campaign, whichfacilitated an adaptive management strategy and constantreviews of hunting efficiencies and escape rates (Lavoie et al.2007).

Flexibility in methods, as well as integration, alsocontributed to eradication success and affected operationalcosts. For example, using hunting corrals early in thecampaign reduced total costs by �US$700,000. As im-portant, corrals resulted in near-zero escapes, which furtherreduced costs by not educating goats to evade huntingmethods. In some situations local factors can conflict withoptimal strategies dictated by an eradication ethic. Forexample, importation problems delayed the use of helicop-ters for aerial hunting, and thus, we relied heavily on groundhunting despite the higher costs. If aerial hunting wereavailable at the beginning of the campaign, total eradicationcosts and duration would have been substantially reduced.By using almost exclusively aerial hunting, we removedapproximately 59,000 goats from Isabela Island for approx-imately US$3.7 million in ,3 years (Isabela Island is .7times larger than Santiago Island; K. Campbell, unpublisheddata). Cost per hectare to remove goats on Isabela Islandwas US$8 compared with US$105 on Santiago Island.Aerial hunting by helicopter was cost effective, even incountries like Ecuador, where labor costs were inexpensive(e.g., average monthly salary of ground hunter was US$550).

The Santiago Island JG program was the first large-scale,systematic deployment of JGs. Other JG programs to date

Figure 7. Sex ratio of remnant goat population during the Judas goat (JG)phase of the Santiago Island eradication campaign (Jun 2004 to Nov 2005).Feral goats (grey line) are goats shot that were not associated with JGs.Associated goats (black line) are goats killed that were associated with JGs.

Cruz et al. � Eradication in the Galapagos Islands 197

have been small, with the largest programs having ,30 JGs,compared with 213 JGs on Santiago Island (Keegan et al.1994, Rainbolt and Coblentz 1999, Campbell et al. 2004).Back-calculating from kill data (not accounting for repro-duction), Santiago Island goat density was, on average,approximately 0.02 goats/ha, when we initiated the JGphase, a density consistent with previous JG programs (0.01goats/ha and 0.02 goats/ha on Pinta and San Clementeislands, respectively; Keegan et al. 1994, Campbell et al.2004). Goats become difficult to detect from a helicopter atdensities ,0.01/ha, and subsequently, cost per kill canincrease substantially (Pople et al. 1998). Although densitiesare rarely known a priori and properly translating kill perunit of effort is always challenging, 0.01–0.02 goats/ha maybe the optimal density to switch from hunting to JGs duringgoat eradication campaigns.

Mata Hari goats appeared to have removed males from theferal population at an elevated rate. Sex ratio of goats killedin the last months of the JG phase was highly skewedtoward females, which may have affected the reproductiveability of remnant females. This hypothesis is supported byobservations of barren females without kids during the JGphase (K. Campbell, unpublished data). In contrast, goatpopulations hunted to low densities elsewhere often increasetheir reproductive rate (Parkes 1984). Along with decreasingremnant population reproductive rates, a lack of maleswould encourage feral females to remain in estrus and searchfor mates, possibly increasing the probability of beingdetected by JGs (Campbell et al. 2005). The observed effectof Mata Hari goats may be an additional benefit toeradication campaigns by reducing total number of pregnantferal females. Some females with kids tend not to associatewith other goats for short periods of time and consequentlymay not be detected with JGs (O’Brien 1984). Such asocialbehavior could result in a longer and more costly eradicationcampaign.

Although cost of checking a JG by ground hunters was 9-fold higher than using a helicopter, cost per goat killedbetween the 2 methods was comparable when we includedtotal number of goats (i.e., JG associated and nonassociatedgoats) because ground hunters with dogs detected and killedmore nonassociated feral goats than did aerial crews.Despite comparable costs, however, aerial hunting is likelyto be more effective in most situations because of differencesin required effort. For example, we could check all JGs onSantiago Island in 2–3 days by helicopter, whereas 1–2months were required to check JGs by ground hunters.

Although JGs facilitated removal of most remnant goatstoward the end of the campaign, they did not remove thelast goat. In the Santiago highlands, ground hunters withdogs working in rastrillo killed the last 23 goats. In thedense vegetation of the Santiago highlands, remnant goatshad small home ranges and JGs deployed in the area oftenstayed within 50 m of their deployment point (K. Campbell,unpublished data), which supports the claim that variousterrain or vegetation types offer refuge for goats from one ormore hunting methods (Forsyth et al. 2003). A range of

methods, used sequentially and simultaneously, was requiredto put all animals at risk.

The cost of removing the last 1,000 goats on SantiagoIsland and subsequent monitoring for confirmation wasapproximately US$2.5 million (40% of entire eradicationcampaign cost). Applied research would likely reduce thefinal investment needed to reach eradication. For example,during JG operations, 80% of the time that we checked JGsfor associated goats, we either found them dead (4%), alone(31%), or associated with other JGs (45%); there was noneed to check JGs. Telemetry or GPS collars that providedreal-time information on whether JGs were alone, withother JGs, or with feral goats would result in substantialsavings (e.g., x¼US$135/aerial JG check). Further, appliedmodels that integrate aspects of search and detection theory,fisheries biology, and economics would help optimize thepoint to switch from hunting to monitoring to declaringsuccess (Benkoski et al. 1991, Campbell and Donlan 2005,Morrison et al. 2007, Baxter et al. 2008). Given thesubstantial costs of removing the final goats of aneradication campaign, such quantitative decision-supporttools could result in substantial savings.

Throughout the campaign, we attempted to document andmitigate for ecological responses of the eradication. Forexample, nonnative plants have increased on some islandsfollowing nonnative herbivore eradication (Bullock et al.2002, Kessler 2002). Anticipating similar dynamics, weintegrated an invasive-plant eradication program. Ninepopulations of invasive plant species were eradicatedconcurrently with goat removal (A. Tye, Charles DarwinFoundation, personal communication; V. Carrion, Galapa-gos National Park, unpublished data). Two invasive plantsthat responded favorably to goat removal proved difficult tocontrol. After not being reported for .20 years, blackberry(Rubus niveus) appeared and increased in distribution onSantiago Island (L. Calvopina, Galapagos National Park,personal communication). Control efforts are underway anderadication is likely possible (Buddenhagen 2006). Efforts tocontrol comb bushmint (Hyptis pectinata) as it expandedthroughout the Santiago Island highlands have beenineffective.

Ecological benefits of goat eradication are already apparenton Santiago Island (Fig. 2). Estimated densities of theendemic Galapagos rail increased by .10-fold comparedwith 1986 when pigs, donkeys, and goats were present(Donlan et al. 2007). Long-term plant and tortoisemonitoring should reveal other ecological changes; however,those changes will take longer to fully document and shouldbe viewed in the time frame of the dominant longer-livedspecies, such as prickly pear cacti (Opuntia spp.; Hamann2004).

MANAGEMENT IMPLICATIONS

Future invasive mammal-eradication strategies should bedriven by the local sociopolitical environment and bestpractices that have emerged from recent large-scale, fast-paced eradications. Because economies of scale decrease cost

198 The Journal of Wildlife Management � 73(2)

per hectare of eradications, investment in specializedmethods, such as aerial hunting and JGs, are cost-effectivefor large goat-eradication campaigns. For large islands, a JGcampaign should be implemented using females andincorporating both quarantine and field-sterilization pro-grams. Hormone implants, which increase estrus by 6–16-fold, require little extra economic or time investment andshould be incorporated (Campbell et al. 2005, 2007). Foreradication campaigns on smaller islands, male JGs may bedesirable because they cost less to sterilize, and removingmales at a faster rate has fewer advantages on smaller islandsbecause fewer goats should remain at the onset of a JGprogram. In hindsight and barring the local sociopoliticalenvironment, aerial hunting would have been the swiftestand most cost-effective method to remove most goats onSantiago Island. Following the initial population reductionwith aerial hunting, highly trained hunters and dogs, usingonly the rastrillo method with aerial support, along with aJG program, would have been the most cost-effectivemethod to systematically hunt the remnant population and,more importantly, to minimize goats escaping huntingevents.

The Santiago Island campaign demonstrated that islandspreviously thought to be too large for eradication are nowwell within limits. Integration of ground and aerial huntingtechniques, combined with the use of specialist huntingdogs, advanced JG techniques, and GIS facilitated asuccessful, swift, and cost-effective eradication. At least forgoats, island size is arguably no longer the limiting factor foreradication campaigns. Future challenges will involveremoving invasive mammals from large, inhabited islandswhile increasing the cost effectiveness of removing low-density populations and confirming eradication. Thosechallenges will require leveraging technology and applyingtheory from other disciplines, along with conservationpractitioners working alongside sociologists and educators.

ACKNOWLEDGMENTSWe express our gratitude to the Galapagos National ParkService (GNPS) hunters and HeliPark pilots and crews whomade this conservation action possible. We thank E. Cruzand R. Bensted-Smith, Directors of GNPS and CharlesDarwin Foundation (CDF) for putting together the bi-institutional initiative, Project Isabela (PI), and we thankthe directors after them for their support. We thank L.Cayot who managed PI between 1997 and 1998, the 1997Feral Goat Eradication Program for Isla Isabela workshopparticipants, and M. Patry who managed PI between 1998and 2002. We thank B. Coblentz, G. Halverson, C.Harrison, R. Henderson, N. MacDonald, J. Parkes, T.Poulsom, H. Snell, R. Suber, G. Woodhouse, and the manyvolunteers for their support. Funding was provided byGNPS, CDF, Galapagos Conservancy, Lindblad Expedi-tions, and English, German, and Swiss Friends ofGalapagos Organizations in collaboration with projectECU/00/G31 Control of Invasive Species in the GalapagosArchipelago, a donation from the Global EnvironmentFacility (GEF) to the Ecuadorian government, represented

by the Ministry of Environment. The project was imple-mented by the United Nations Development Program(UNDP) and was executed by the GNPS, CDF, NationalInstitute for Galapagos, and the Ecuadorian Service forAgriculture and Livestock Sanitation–Galapagos. TAMEairline, Cornell University, and Island Conservation pro-vided additional support. Opinions expressed herein belongto the authors and do not necessarily reflect the opinions ofGEF or UNDP. This is CDF contribution 1034. N.MacDonald, B. Coblentz, and an anonymous reviewerimproved this manuscript.

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Associate Editor: Grado.

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