Rat Eradication Plan for the Cocos (Keeling) Islands
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Rat Eradication Plan for the Cocos (Keeling) Islands February 2020 1. Background Parks Australia (Christmas Island National Park and Pulu Keeling National Park) is attempting to move and introduce the Critically Endangered Christmas Island blue-tailed skink (Cryptoblepharus egeriae) to suitable islands within the Cocos (Keeling) Islands through an assisted Conservation Introduction. This program seeks to secure the species from extinction and provide an alternative to wild release on Christmas Island where introduced predators are still extant. To maximise the chances of success, eradication of black rats (Rattus rattus), a suspected predator of C. egeriae and its eggs will be attempted on selected destination islands along with other predator removal activities. Ongoing research as well as monitoring for, and management of rat recursions are also planned. The islands within the southern atoll of the Cocos (Keeling) islands is Commonwealth land managed in trust by the Cocos (Keeling) Shire Council (CKSC). Land ownership will not change with the introduction of C. egeriae and the responsibility for future land management will remain with CKSC. Implementation of rat eradication and ongoing surveillance/management will remain the responsibility of Parks Australia. This plan provides a broad eradication strategy that can be adapted accordingly to suit each of the selected destination islands and will generally take four weeks to implement. A site specific plan will also be developed for each of the selected destination islands and attached to this plan over the life of the program. 2. Methods 2.1. Establishment of ‘rat removal locations’ Using GIS establish a 25mx25m grid across the island. An example is provided in Figure 1. At each waypoint a suitable site will be chosen to establish a bait station and/or trap. Some sites may be moved by up to 20m depending on site access, suitability of location as rat habitat or deployment substrate (e.g. sand, submerged by tides etc.). Some sites may require a little clearing. Up to four days may be required to prepare the rat removal locations prior to the commencement of removal activities. This will depend on the size and location of the destination island. Camping may also be required on some islands during all phases of the eradication attempt. NOTE: Rat eradication by DBCA on Direction Island was achieved using a grid of 20mx20m, however, eradication was achieved using only toxic baits, whereas this campaign will employ both trapping and baiting techniques.
Figure 1: Example of proposed rat removal locations on Pulu Blan
2.2. Baiting
At each of the established rat removal locations deploy four X-Verminator rat baits. Baits will be
secured either with wire or nails to an elevated tree branch/trunk, secured with wire/nails directly to
an elevated tree branch/trunk, or secured in a bucket (Figures 2 and 3). If a PVC tube or bait bucket
is used for the deployment of bait, coconut milk will be used as an additional lure around the tube or
bucket opening.
Baits will be checked daily for the first 10 days and serviced as necessary (i.e. baits refreshed, spoiled
baits removed). Following this, the frequency of checks will reduce to approximately weekly until the
end of the four week campaign. At the end of the four week campaign baits will be left in-situ and
removed at a later date. Bait take, spoilage and non-target consumption will be recorded at each
check.
Coopextm insecticide will be applied to the entrance of the station should ants or other insects be
found accessing the bait.
Canopy baits will be deployed strategically within Cocos nucifera forested areas to fill in gaps
between the rat removal locations (Figure 4). Canopy baits will be deployed in the following way:
Attach a 100 gram sinker to the end of a 3mm polymer rope;
Throw the weighted end of the rope towards the crown of the tree so that it comes through
to the other side of a branch;
Once weighted end is retrieved, remove the sinker, thread three baits onto the rope and tie
the two ends together to form a loop.
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Raise the baits into the canopy by pulling down on the rope like a pulley system. Ensure the
baits are in contact with a suitable substrate that rats can easily access (e.g. palm frond);
The end of the loop should then be secured to a nearby tree so that it can be easily
accessed for bait checking and retrieval.
Figure 2: Rat bait/trap secured in bucket Figure 3: Rodent Bait secured directly to tree branch
Figure 4: Canopy bait
2.3. Trapping
Two to four durable rat snap traps will be deployed at each rat removal location 14 days after the
initial poison bait deployment using one or a combination of lures including cheese, peanut butter,
or carrot coated with coconut milk.
The traps will be attached to an elevated tree branch using wire or nails (Figure 5) or secured in a
bucket (see Figure 2) to prevent crabs accessing the traps. The traps will be checked daily for a
period of 14 days with records taken of rat kills and lures refreshed as required. From early in the
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campaign, assessments on the most effective lure will be made with this lure to be used as
preference.
Trapping will conclude after a period of 14 nights. Trapping will continue beyond the initial 14-night
campaign if any rats are trapped in the final two days of trapping. Traps will be removed after the
final trapping night.
Figure 5: Rat trap attached to tree
2.4. Monitoring
Three chew cards (corflute) baited with peanut butter elevated off the ground (Figure 6) will be
deployed at every second station in week four of eradication activities (or sooner if bait take is zero)
and checked twice per week for the first two weeks and every seven days for a further period of four
weeks to detect rat activity.
Beyond this, chew card deployments/checking will occur at every fifth station every three months
indefinitely to monitor for rat presence. Where applicable, one of these chew cards will be deployed
into the C. nucifera canopy using a stringline.
Should bait-takes become absent very early in the eradication attempt, chew cards will be deployed
early to assess if eradication has already been achieved or if rats are avoiding the baits, in which case
a reassessment of bait/deployment technique will be required.
Figure 6: Rat monitoring ‘chew card’ baited with peanut butter
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Four gas-fired Goodnaturetm rat traps with kill-counters will be deployed on each island at or prior to
commencement of eradication activities. Initially they will be checked whenever staff are on island
and every three months beyond this for rat presence.
To prevent crabs interfering with the traps, they will be deployed at least 1m off the ground on C.
nucifera. Also, a thin, 5cm band of smooth plastic will be wrapped around the tree below the trap to
prevent crabs from accessing the trap. To check that crabs are not being killed by the trap, a
collection bucket with drainage holes and escape routes for living invertebrates will be secured
directly below the trap to collect crushed crab shells (Figure 7).
Figure 7: Collection bucket
Four Scoutguardtm cameras will be deployed on each island focused on the gas-fired rat traps and
checked every three months for rat presence.
3. Work schedule
The following work schedule (Figure 8) is a best-case scenario for time and effort to carry out rat
eradication and monitoring on the destination island and does not take into account tidal access or
preparation of traps.
Figure 8: Proposed rat eradication and monitoring work schedule
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4. Cost and equipment
It is expected that significant PKNP/CINP staff time (up to 400 person hours per-island) and some
camping on the islands is required to achieve successful eradication. For the peak five-week period
an additional staff member may be required on Cocos to help facilitate the eradication.
Table 1: Estimated equipment costs for rat eradication per island (based on the larger island of Pulu
Kembang).
Item Minimum cost per island
2x Return flights from CI to Cocos $570
APS 3 for 2x5 weeks (non-cocos staff) $8,430
Accommodation for 2x5 weeks (non-cocos staff) $8,250
Travel allowance $3,225
3,300 Pestoff Rodent Bait 20Rtm rat baits (enough for up $1,300
to 32 baits deployed per-station)
Rat traps x 250 (for use on both islands) $800
8x Goodnaturetm rat traps $800
100, 16x8cm Chew cards (corflute) $70
Motion sensing camera Nil (already acquired)
Lure (Peanut butter etc.) $100
Consumables (fuel, Coopex, wire, nails etc.) $350
Bait/trap stations Nil (already acquired)
Transport of bait buckets and PVC stations from CI to $400
Cocos
TOTAL $24,295
5. Outcomes
Should eradication be successful, the islands will be ready for the conservation introduction of C.
egeriae. A final report will be written detailing the success or otherwise of the eradication effort.
6. Biosecurity
Reinvasion of rats to the islands is a risk and there are two possible routes for this to occur;
1) Assisted/accidental reinvasion
Rats are able to reinvade through lapsed biosecurity and reinvade via vessels/craft arriving on the
islands. Following the conservation introduction of C. egeriae to the destination island(s), it is not
our intention to prevent community or other access of the island(s). Whilst visitation outside of
those working on the conservation introduction is low, this risk will be mitigated through a detailed
community education campaign (including a biosecurity checklist) to encourage vessel owners to
thoroughly check vessels in order to minimise the risk of rat reinvasion. Escorted visits may be
considered in the future if the conservation introduction of C. egeriae generates community interest.
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Visits by those working on the conservation introduction (e.g. monitoring) will occur on an ongoing
basis. To mitigate this risk a biosecurity checklist will be developed for host island visitation to
include for example; vessel checkpoints, foodstuffs repacked in plastic containers equipment (e.g.
camping equipment) checked and re-packed etc.
2) Natural reinvasion.
Rats reinvade the island(s) unassisted and are able to do so by swimming or ‘hitching a ride’ on
debris (e.g. floating vegetation). The frequency of reinvasion is unknown and it could be months to
decades between reinvasion attempts. For example, reinvasion following eradication on Direction
Island occurred within two years whilst rats are still yet to invade Horsburgh Island on the southern
atoll and the more remote North Keeling Island after more than 150 years of human settlement.
Control or eradication on neighbouring islands to those selected as destination islands may not be
feasible depending on their size. Despite the risk of ‘unassisted’ reinvasion from neighbouring
islands, rat control/eradication activities on these islands are not planned.
7. Contingency and review
There are three possible outcomes following the rat eradication efforts; (1) rats are successfully
eradicated and do not reinvade, (2) rats are successfully eradicated and later reinvade, (3) rats are
not successfully eradicated.
1) Should rats be successfully eradicated and do not reinvade, monitoring should continue as long
as the conservation introduction of C. egeriae to the host island is successful and C. egeriae
remain present on the island.
2) Should rat eradication be successful and later reinvade, eradication may be attempted for a
second time using the same techniques detailed here, or others if recommended in the final
report as long as the conservation introduction of C. egeriae to the destination island is
successful and C. egeriae remain present on the island. Control, rather than eradication may be
considered should it appear that the impacts of low-density rat populations on the island(s) on
C. egeriae be minimal and the frequency of reinvasion events be high.
3) Should rats not be successfully eradicated, a review will take place on the methods employed
complete with recommendations presented in the final report. Further expert advice will be
sought on future potential eradication or control attempts, further C. egeriae releases may be
delayed until rats are completely removed and advice will be sought from CIRAP on if/how to
proceed with the conservation introduction of C. egeriae to the destination island(s).
The implementation of this plan should be flexible and adaptive.
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