Papasula abbotti (Abbott’s Booby): There has been much concern about the impact of Yellow Crazy Ants on the endangered listed species, Abbott’s Booby, which now nests only on Christmas Island but used to nest on many other islands in the Indian and Pacific Oceans (Garnett & Crowley 2000). The conservation status of this seabird has been of concern since the 1960s and its conservation was central to the creation of the Christmas Island National Park. It has been observed that as of September 2002, 12% of the population nested in ant-infested areas and that 96% of all Abbott’s Booby nests are found in the canopies of species of trees that are preferred by Yellow Crazy Ants. This species has a low intrinsic rate of increase and previous studies have shown that even a small decline in breeding success could have significant long-term consequences for the population (Olsen 2002). A study has been conducted comparing the density of breeding sites of Abbott’s Boobies in areas that contain supercolonies with those that do not, and no significant differences were found. A similar comparison was undertaken for non-breeding sites of Abbott’s Boobies (roosting sites) and a small, significant decline was found in the number of birds using non-breeding sites in areas containing supercolonies. It was also found that nest success did not differ significantly between ant-infested and intact forest. However, it is considered that this study was limited, being designed to detect only very large impacts caused by Yellow Crazy Ants. A recent survey of nests did not indicate a change in nest activity around Yellow Crazy Ant distributions (Olsen 2002). Experts still consider that given the importance that minor variation in breeding success might hold for the species, there are insufficient data to conclude that Yellow Crazy Ants do not pose a serious threat to Abbott’s Booby. Yellow Crazy Ants have been recognized as potentially the most serious threat to Abbott’s Bobby in the draft recovery plan for Abbott’s Booby (Olsen 2002).
There is sufficient information to suggest that this threatening process may be impacting on the Abbott’s Booby, and is adversely affecting this species. However, there is insufficient data to indicate the extent of this impact, and whether the species may become eligible to be listed in a category representing a higher degree of endangerment as a result of this process.
Fregata andrewsi (Christmas Island Frigatebird): This is the rarest endemic seabird on Christmas Island and is listed as vulnerable under the EPBC Act. It breeds in tall trees in terrace forests in only three small areas totalling about 170 ha in extent. The total population size, last estimated in the early 1980’s, was approximately 1620 pairs. The recovery plan for this species (Hill & Dunn 2004) includes the impact of Yellow Crazy Ants as a threat. The ants are considered to potentially threaten individual breeding birds as well as the nesting trees. Christmas Island Frigatebirds are especially at risk from Yellow Crazy Ants because supercolonies concentrate on terrace forests of the islands where all Christmas Island Frigatebirds nesting habitat occurs.
There is sufficient information to suggest that this threatening process may be impacting on the Christmas Island Frigatebird, and is adversely affecting this species. However, there is insufficient data to indicate the extent of this impact, and whether the species may become eligible to be listed in a category representing a higher degree of endangerment as a result of this process.
Accipter fasciatus natalis (Christmas Island Goshawk): This subspecies is currently listed as endangered under the EPBC Act. It is considered to be the rarest endemic land bird on Christmas Island, and it occurs in all habitats from primary and marginal rainforests to suitable areas of secondary regrowth vegetation. The recovery plan (Hill 2004a) states that the total population size may be as few as 100 adults, and is probably limited by the availability of suitable rainforest habitat. It considers that Yellow Crazy Ants pose a potentially critical threat to the survival of this bird.
As such large areas of Christmas Island rainforest have been disrupted by this threatening process, there is sufficient information to suggest that this process may be impacting on the Christmas Island Goshawk, and is adversely affecting this species. However, there is insufficient data to indicate the extent of this impact, and whether the species may become eligible to be listed in a category representing a higher degree of endangerment as a result of this process.
Ninox natalis (Christmas Island Hawk-Owl): The Christmas Island Hawk-Owl is endemic to Christmas Island, and is currently listed as vulnerable under the EPBC Act. The recovery plan (Hill 2004b) states the species’ territories are found in all habitats, and the total population is estimated to be about 820-1200 birds. The recovery plan considers supercolonies of the introduced Yellow Crazy Ant to potentially pose an extreme risk to this species. There have been no specific studies on the impact of Yellow Crazy Ants on Hawk-Owls, but it is considered that if the birds were grounded for some reason, ant supercolonies would most probably result in the death of the bird. Although research has shown that Yellow Crazy Ants have little impact on canopy insects, these studies are considered limited, and it is possible that the ants may reduce insect populations, the primary prey of the Hawk-Owl (Hill 2004b).
There is sufficient information to suggest that this process may be impacting on the Christmas Island Hawk-Owl, and is adversely affecting this species. However, there is insufficient data to indicate the extent of this impact, and whether the species may become eligible to be listed in a category representing a higher degree of endangerment as a result of this process.
Impacts on listed threatened reptiles
The two rarest endemic Christmas Island reptiles are the vulnerable Lepidodactylus listeri (Christmas Island Gecko) (a primary forest species last recorded in 1979, when it was relatively abundant) and the Ramphotyphlops exocoeti (Christmas Island Blind Snake), last seen in 1975. Both are found in areas where Yellow Crazy Ant supercolonies have formed and are located in microhabitats where Yellow Crazy Ants forage intensively.
Lepidodactylus listeri (Christmas Island Gecko): This is a small nocturnal lizard that forages from the lower trunk to the canopy of large forest trees. It is considered that both eggs (laid under the bark of rainforest trees) and individuals may be vulnerable to direct predation by Yellow Crazy Ants. Cogger & Sadlier (1999) were unable to account for an absence of this species in a 1998 survey of the island compared to an earlier one in 1979. They suggested a marked decline had occurred and that Yellow Crazy Ants may be implicated though were unlikely to be the principal threatening process, as many of the survey areas where the Gecko had been found in 1979 were free of ants in 1998. With the spread of Yellow Crazy Ants since 1998, it is likely that Christmas Island Gecko, already under threat, has been adversely affected by Yellow Crazy Ants. The direct effects of Yellow Crazy Ants on the shrew are unknown, but it is likely that breeding, shelter and foraging sites would be severely affected. It is also likely the ants would kill young animals in the nest and, possibly, adults in severely affected areas (Schulz 2004).
This threatening process is considered to be adversely affecting the Christmas Island Gecko, and it could become eligible to be listed in a category representing a higher degree of endangerment as a result of this process.
Ramphotyphlops exocoeti (Christmas Island Blind Snake): This is a burrowing snake that has a number of adaptations to avoid both biting and spraying ants, and might even prey on the Yellow Crazy Ant colonies. Its subterranean habits would make it difficult for the ants to attack it in large numbers. There is little evidence at present that this species is being affected by Yellow Crazy Ants.
Turtles: Yellow Crazy Ants may also represent a threat to hatchling turtles. Small numbers of Chelonia mydas (Green Turtles) and very occasionally Eretmochelys imbricata (Hawksbill Turtle) nest on sandy beaches of Christmas Island. Both these species are listed a vulnerable. Yellow Crazy Ants are reported to forage on sandy beaches on Christmas Island, in Micronesia, and in the Seychelles (Townes 1946; Feare 1998; unpublished observations). On Christmas Island, there is little information or data on the likely affect of this process on the Green and Hawksbill Turtles.
Conclusion to B: Based on the information available and summarized above, the TSSC considers that the threatening process:
has the potential to cause a number of nationally listed threatened species to become eligible for listing in another category representing a higher degree of endangerment. These species are the: Pipistrellus murrayi (Christmas Island Pipistrelle), Crocidura attenuata trichura (Christmas Island Shrew) and Lepidodactylus listeri (Christmas Island Gecko).
Therefore the threatening process is eligible under this criterion.
Conclusion to C: There is considerable data indicating that Yellow Crazy Ant supercolonies have caused major changes in the Christmas Island ecosystem. These changes are likely to represent profound alterations to threatened species habitat, and it is reasonable to conclude that they are most likely adversely affecting threatened species. While the threat abatement activity (outlined below) has been successful in destroying Yellow Crazy Ant supercolonies, it is too early to evaluate how well the ecosystem has recovered and the consequences that Yellow Crazy Ants have had on threatened species. Also, at this stage, threat abatement is aimed at suppressing Yellow Crazy Ant supercolonies, and it may not be possible to completely eradicate Yellow Crazy Ants from Christmas Island.
Therefore, the TSSC considers that:
this threatening process adversely affecting two or more species listed under the EPBC Act. These species are: Pipistrellus murrayi (Christmas Island Pipistrelle), the Christmas Island Shrew (Crocidura attenuata trichura), Papasula abbotti (Abbott’s Booby), Fregata andrewsi (Christmas Island Frigatebird), Accipter fasciatus natalis (Christmas Island Goshawk), Ninox natalis (Christmas Island Hawk-Owl) and Lepidodactylus listeri (Christmas Island Gecko).
Therefore the threatening process is eligible under this criterion.
CONCLUSION –The abatement actions that are being undertaken to eliminate Yellow Crazy Ant supercolonies have been highly successful. However, the actions are ongoing, and the full eradication of Yellow Crazy Ants on Christmas Island is unlikely at this stage. It has been shown that Yellow Crazy Ants can very rapidly spread through the rainforest of Christmas Island, threatening many species and profoundly altering the functioning of the ecosystem. The threatening process meets s188(4)(a), s188(4)(b) and s188(4)(c) of the EPBC Act. The threatening process could cause a native species or ecological community to become listed as threatened, could cause listed threatened species to become listed in another category representing a high degree of endangerment and adversely affects 2 or more listed threatened species (other than conservation dependent species).
3. Threat Abatement Plan
Current situation and control activity
Christmas Island National Park Management Plan: The Yellow Crazy Ant invasion has been recognized in the Christmas Island National Park Management Plan (2002) as a key threat to biodiversity on Christmas Island. The Management Plan specifically states that a program to research, control, manage and monitor the impacts of the Yellow Crazy Ant will continue as a high priority.
Action Plan for Invasive Ants on Christmas Island: Management and threat abatement of Yellow Crazy Ants on Christmas Island is currently being addressed in the Action Plan for Invasive Ants on Christmas Island (Action Plan) which is overseen by the Christmas Island Yellow Crazy Ant Steering Committee. This committee is made up of representatives from government agencies, including Parks Australia, and experts. This Action Plan has been operational for about four years and the current Action Plan (PANCI 2003) prescribes three years of forward planning. Its primary aim is to eliminate Yellow Crazy Ant supercolonies using fipronil-based baits; island-wide eradication of the species is not a current goal. Control is achieved using a fish-meal bait with the active constituent of fipronil, a broad spectrum, neurotoxic insecticide. Research, monitoring of target and non-target impacts, surveillance, and community awareness and education are also key components of the Plan. The program has progressed from a focus on experimental ground baiting in 2000-2001 to an island-wide aerial baiting campaign in September 2002. Combined, these efforts treated almost 2900 ha (371 ha by foot, 2500 ha by helicopter) of ant-infested forest. Wherever bait was dispersed, knockdown of supercolonies has been immediate and impressive. Overall, baiting resulted in a 98-100% reduction in ant activity within two weeks, with very few identifiable non-target impacts (Green 2002).
This Action Plan and its results to date indicate that the impacts of Yellow Crazy Ants on Christmas Island can feasibly, effectively and efficiently be abated through such an approach.
Threat Abatement Plan (TAP) for Tramp Ants in Australia: The TSSC’s advice for listing the key threatening process: ‘The reduction in the biodiversity of Australian native fauna and flora due to the red imported fire ant, Solenopsis invicta’ recommended:
The development of a threat abatement plan, which provides a national framework to mitigate the potential impact of the group of ants known as tramp ants (including the fire ant), is considered to be a feasible, effective and efficient way to abate the impacts of these species. This TAP should not duplicate activities already underway in Queensland, but focus on actions such as public education, surveillance and monitoring, quarantine and border control, and development of contingency plans in the other States and Territories.
The Yellow Crazy Ant is one of those tramp ants that will form part of this TAP. This TAP will focus on issues of preventing and responding to new invasions rather than detailed actions that abate advanced invasions such as that of the Yellow Crazy Ant on Christmas Island.