Feral Pig Eradication Campaign on Santiago Island_ Galapagos

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					             Feral Pig Eradication Campaign on Santiago Island, Galapagos1
                             Marc Patry, Charles Darwin Research Station
                               Casilla 17-01-3891 Quito, ECUADOR

Feral pigs (Sus scrofa) are considered one of the most ecologically destructive introduced
vertebrates in Galapagos, where they are effective predators of giant tortoise and sea
turtles nests, possibly prey upon young tortoises, and in certain circumstances, compete
for food resources with young giant tortoises (MacFarland et al, 1974a, Green et al, 1982,
Coblentz, 1987). On Santiago island (58,465 ha) pigs have been responsible for a near
zero recruitment rate of giant tortoises, whose numbers had already been critically
depleted after centuries of human exploitation (ibid).

The Galapagos National Park Service (GNPS), and the Charles Darwin Foundation
(CDF), both created in 1959, focused on the conservation of the giant tortoises as one of
their first priorities – the CDF carrying out research to support management activities
carried out by the GNPS. In 1964, the CDF established the Charles Darwin Research
Station (CDRS) in Galapagos and within a year established an ex-situ tortoise breeding
centre. The first Santiago island tortoise eggs were brought to the breeding centre in
1970 for hatching and rearing (Cruz et al., 1999). By 1973, active pig control campaigns
were established on Santiago in an effort to increase natural recruitment rates.

The past 30 years have seen a waxing and waning feral pig control efforts. These
variations were related to funding availability, El Niño events, morale fluctuations, or
lack of training. Despite periods of frustration, the GNPS is now very close to having
reached its objective. Only one pig has been observed (dead) since May 2000 despite
intensive on-going monitoring. The campaign will not be officially completed until an
arbitrarily set 18 month monitoring period for pig sign reveals no further evidence of
their presence.

This paper provides a descriptive account of the pig eradication effort since 1997, when
both the GNPS and the CDRS made the program a bi-institutional priority, allocating it
necessary funding and staff.

Fundamentals of an eradication campaign
Many efforts to eradicate an introduced species have failed for a variety of reasons.
Several factors have been identified as contributing to a successful eradication campaign
(Myers, J. et al, 2000). For the Santiago pig eradication, the relevant factors are:

        i)       Sufficient resource to fund the campaign to its conclusion: The
                 Santiago pig control/eradication campaign, from 1973 to 1996, had been
                 plagued by unstable funding. Until 1998, GNPS budgets were allocated
                 centrally, in Quito, in competition with the demands of many other
                 government institutions, resulting in an inability to ensure long term stable

 Referenced as: Patry, M. 2001. Feral Pig Eradication Campaign on Santiago Island, Galapagos. In
Informe Galapagos 2001. Fundación Natura, Quito (in press).
               funding to specific programs. Growing support from the CDF fundraising
               efforts, along with important budget allocation changes at the GNPS
               helped provide stable funding starting in the late 1990’s.
       ii)     The species must be detectable at low densities: Throughout the first 24
               years of the pig campaign, densities never reached such low values as to
               create problems in detection by the methods used (fig. 2 illustrates how
               hunting effort per pig removed remained relatively low until 1996).
               Groups of hunters and their dogs were sufficiently trained and covered
               enough territory to be able to detect pigs on the island by direct
               observation of pigs, or pig sign, at all times. However, as densities
               declined, hunting effort per pig removed began to climb rapidly by 1997.
               By 1999, densities reached levels so low as to require the use of
               widespread baiting in order to detect pigs. This method was successful in
               detecting a pig in November 2000, 6 months after the baiting campaign
               was established, and during which time no visible sign of pig had been
               observed by hunters or dogs. This detections suggests the ability to detect
               possible a single pig on the entire island.
       iii)    All individuals must be at risk: Extensive areas of dense vegetation on
               Santiago effectively created refuges where pigs were safe from hunters
               and their dogs. The development and maintenance of a extensive trail
               system throughout these areas increased vulnerability of the pigs
               throughout their range, permitting hunters and their dogs to more easily
               flush pigs out from their cover.
       iv)     The risk of re-invasion must be controllable: The only means through
               which pigs could re-establish themselves on Santiago island is through
               deliberate introduction by humans. This risk is being managed by the

By the end of 1996, sporadic control efforts had been on going for 24 years. During that
time, 18,903 pigs were removed from Santiago (Calvopiña, J. 1985, Calvopiña, L. 1989,
Isabela Project, 2000) and a valuable study on pig distribution, reproduction and
territoriality was conducted (Coblentz, B. and D.W. Baber, 1987). However, during the
few years prior to 1997, especially from 1991 to 1994, funds were cut back and
enthusiasm waned, resulting in dramatic reduction in hunting effort.

Figure one illustrates that the average trimester hunter effort (measured as [#hunters +
#dogs]x #hunting days) during the 1991-94 period was 419 hunter-dog-days (hdd’s)
compared to average for all other years of 1,034 hdd’s. Figure 1 also illustrates how the
low hunting effort during the 91-94 was followed by a large increase in pigs killed in
1995, when hunting effort was more than doubled. These numbers may suggest how
rapidly the pig population responded to reduced hunting pressures.
1997- Renewed bi-institutional commitment
In mid-1997, the Santiago pig eradication program was given renewed priority status by
both the GNPS and the CDRS. The project’s management was transferred to the Isabela
Project, a newly created bi-institutional project whose longer-term objective was the
eradication of goats from northern Isabela Island. This management structure helped
ensure the commitment of both institutions, including allocations of staff and funds.

These changes resulted in a near doubling of hunting effort from 1996 to 1997 (from 711
to 1,368 hdd’s per trimester), though hunting strategies remained the same. Typically, a
group of 10 to 12 GNPS hunters usually with one dog each were sent to Santiago on trips
of 8-10 effective working days (not including travel time). Hunters alone, in pairs would
carry out loosely coordinated searches of pig habitat on Santiago. Every evening,
informal debriefing sessions would determine where hunters would focus efforts on the
following day.

1998-99 Stable funding adoption of new technologies
Stable Funding
The passing of the Special Law for Galapagos in 1998 provided the GNPS with steady
and guaranteed funding for its operations. These changes allowed the GNPS to make and
keep longer term financial commitments to specific projects. Also, by 1998, a portion of
CDF fund-raising efforts were dedicated specifically to the campaign. Combined, these
efforts helped ensure stable financing of the pig eradication program, a basic requirement
for a sucessful eradication campaign.

New technologies
By the second half of the 1990’s, the CDRS had begun to apply global positioning system
(GPS) and geographic information system technologies (GIS) to field work. The Isabela
Project, with the support from the CDRS department of Vertebrate Ecology and
Monitoring, became one of the first to systematically apply GIS and GPS to a specific
park management challenge. By 1999, hunters had become proficient in the use of GPS
units and regularly returned from the field to download GPS data into ARC-INFO GIS
software on GNPS desk-top computers. The information revealed exactly what terrain
had been covered in their search for pigs (fig. 3). Field computers were acquired in late
1999; with further training, hunters were able to download and evaluate GPS data on site
daily. Hunters who had previously boasted at having covered “every square metre of
terrain” now saw graphic evidence of huge gaps where no hunter had been. This
information helped the hunting team plan the following day’s outing, ensuring that
indeed, all of the pig habitat was being monitored.

GPS and GIS technology was also helpful to re-establish and maintain a 300 km network
of trails through some of the densest vegetation on the island (fig. 3). The trail network,
first used 10 years earlier but abandoned and completely overgrown, helped hunters
access areas of dense vegetation previously used by pigs as refuges to hide from dogs and
hunters. With trails, radios and GPS units, hunters could now range freely throughout
pig habitat, coordinate their movements with extreme precision, and increase the overall
pig hunting effectiveness.

Increased Effort per Pig Removed
Typical of an eradication campaign, as the density of the target species drops, the effort
required per individual removed increases. Figure 2 illustrates the rapid increase in effort
required to remove individuals in the final years of the Santiago campaign. The figures
show that 450 times more effort was required to remove a pig in 2000 than in 1988.
Obviously, this effort comes with a high relative price tag; though the annual cost of the
pig eradication campaign increased by approximately 20% from 1997 to 2000, the actual
cost per pig removed increased by approximately 2,000% during that same period.

1999 Monitoring for pig presence
By 1999, the number of pigs killed per outing was never greater than 3 (see Fig. 1). In
order to increase pressure on the remaining pigs and also, as the start up of a monitoring
phase, the systematic poisoned baiting of pig habitat was initiated. Baiting would
contribute to increasing the pressure on any remaining pigs and provide an indication the
number of pigs left – as pig disturbance of baits is easily noted (no Santiago island animal
besides pigs has either the ability or an interest in moving the baits about).

1080 was first applied, with a combination of an anti-emetic (metaclopramide) to ensure
that the ingested poison was not later regurgitated. The poison, in solution, was
injected uniformally via a series of lethal doses throughout goat carcasses, and these were
then placed in areas where hunters thought pigs frequented. Results of the baiting were
conflicting – hunters knew of the on-going presence of pigs on Santiago via the
occasional footprint or characteristic soil disturbance from rooting behaviour, yet the
baiting work often did not reflect a similar presence. Project staff concluded that the pigs
had become bait shy. Early onset of symptoms, characteristic of 1080, are thought to
discourage the pigs from eating a lethal dose andsurviving pigs learn to associate
discomfort with the bait, thus develop bait shyness.

In December 1999, after careful consideration of the poisoning campaing results, the
Isabela Project switched from 1080 to Warfarin, a poison commonly used for rats, but to
which pigs were known to show an unusually high sensitivity. In contrast to 1080,
Warfarin is slow acting, with symptoms appearing well-after a lethal dose is ingested,
thus reducing the chances of pigs associating the baits with negative effects on their
health. Finally, added advantages to using Warfarin included the availability of a simple
antidote (vitamin K), and a much reduced toxicity to dogs, humans and other non-target
species. Warfarin proved to be more effective and practical than 1080 and remains the
poison currently in use.

2000 On-going monitoring and hunting; equidistant baiting
In 2000, the initial practice of placing baits haphazardly in areas where pigs signs had
been observed was replaced by an equidistant baiting approach to ensure that all pig
habitat was uniformly covered. This change marked the transition from erradication
activities to monitoring activities. Using GIS, 500m equidistant georeferenced points
were superimposed on a map of Santiago (fig. 3). Baits were placed and within two
weeks, field staff return to check every bait for tampering. As Warfarin remains active at
all stages of bait decomposition, field staff could afford to let a reasonable amount of
time pass before returning to check for tampering, thus increasing the effectiveness of
their monitoring efforts (Harwood et al, 2000). Between November 2000 and May 2001,
all possible pig habitat was baited twice and each of the approximately 15,000 baits
applied were monitored. The process will be repeated once more in the following 12
months. Should no further pig sign be detected, Santiago will be considered pig free,
though annual monitoring trips will continue.

This 18 month period has been arbitrarily chosen, but is thought to be fairly conservative
given a pig’s gestation period and seasonal changes in food availability for pigs (e.g
during droughts, they woud be more likely to take the bait). The time frame is flexible to
take into consideration uncontrollable events such as El Niño, which would increase
monitoring difficulties and likelihood of survival and reproduction of individual pigs.

May 2001
Despite on-going intensive hunting pressure, no pigs have been shot since May 2000.
Intensive monitoring through systematic baiting was begun in November 2000.
Equidistant poisoned baits were twice applied to all pig habitats, (including areas
considered borderline habitat – the vegetated arid zones of the island) of Santiago, thus
covering a total of 38,344 hectares (66% of total land area) – only lava fields were
excluded. Each bait was monitored approximately two weeks after having been placed.
These efforts led to the detection of pig sign in late November 2000; one pig was
subsequently found dead two weeks later, near the disturbed bait. No other pigs have
been detected to date.

Should the on-going monitoring efforts reveal no further pig sign, the GNPS would
declare Santiago island pig free in May 2002 – the first time in at least 127 years, and the
largest ever island from which pigs will have been successfully eradicated.

The Santiago island pig eradication, though not formally completed, illustrates a series of
elements of value for those wishing to contemplate similar projects elsewhere.

       1. During start up, much is accomplished with relatively little effort. Initial
       removal rates are very high and relatively little effort is required to remove pigs
       (see fig. 2). During this stage, staff is enthusiastic and institutional support

       2. As pig numbers drop, hunting effort per pig increases. Typical outings result
       in far fewer pigs removed. Over time, no definite trend towards fewer pigs
       removed is evident (1990 – 1996), resulting in a realization that on-going control
       or eradication will require an increased and sustained effort. Institutional
       support may falter as there is “no end in sight” of the pig control effort and this
        may trigger a drop in morale by the project leaders. There is a risk of projet
        abandonment at this stage.

  Fig. 3: SPOT image of Santiago island showing: a) a sample of georeferenced 500m equidistant
points, for placement of poisoned baits; b) trail system (black) and c) 4th of October 1998 tracking of
                                     a hunter on a day’s outing.

    3. Project proponents determine realistic levels of hunting effort required for
       eradication. Institutional support is secured for a protracted effort.

    4. Hunter effort increased (1995-present): Recognizing that the effort required to
       remove the last individuals is far greater than at the outset (fig. 2), the institutions
       involved allocate the necessary resources for completion of the eradication
       campaign. Crucial institutional support is maintained despite extremely high
       effort required / pig killed (roughly 450 times increase over 1988).

I would like to thank Gonzalo Banda and Timo Koester, self-taught Isabela Project GIS
techies, for organizing and processing field data. The success of the Santiago pig
eradication campaign is largely due to the indefatigable efforts of Felipe Cruz and the
professional hunters of the Isabela Project, led by Roberto Ballesteros and Wilson
Cabrera. Additional thanks is due to Dr. Howard Snell of the Charles Darwin Research
Station for supporting the Isabela Project in its efforts to adapt GIS and GPS technologies
to field requirements.


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