The Moth and the Pygmy Possum: A Case Study in Assisted Colonization in the face of Climate Change

The Ethics of Assisted Colonization (AC) in the Age of Anthropogenic Climate Change. G. A. Albrecht • C. Brooke • D. H. Bennett • S. T. Garnet. Case Study 1: The ‘‘New Zealand’’ Mountain Pygmy-Possum (Burramys Aotearoa parvus) 2012; Journal of Agricultural and Environmental Ethics.

The Australian Mountain Pygmy-Possum (Burramys parvus) is a little knownanimal that could be among the first wave of species to be rendered extinct by anthropogenic climate change. Three isolated populations of the possum live in an area of 7 km2 in the highest parts of south-eastern Australia (Broome 2008). They live in boulder fields at high elevations and appear to rely on the migratory Bogong Moth (Agrostis infusa) for food, though they also eat a variety of seeds, such as those of mountain plum-pine (Podocarpus lawrenceii). They were widespread when the climate was colder and now face numerous threats in their remaining alpine habitat, many of which are likely to be exacerbated by climate change (Broome 2008). Total population estimates vary from 500 to approximately 1,000 individuals.

While alpine habitat does exist in Tasmania, still within Australia, it is at a lower altitude and so is likely to provide only a temporary climatic refuge should the pygmy-possum be moved there. However, the South Island of New Zealand has a far greater altitudinal range so, hypothetically, could be suitable for the species over a much longer period. There are also close relatives of the mountain plum-pine growing in the New Zealand mountains, although there is no equivalent to the Bogong Moth, a species which, in Australia, aestivates in alpine boulder fields in such large numbers that the collection of moths was once a major feature of Aboriginal livelihoods in the Australian alpine region (Bowdler 1981).

However, three of many complications stand out. First, New Zealand already has one introduced possum species, the Australian Brush-tail Possum Trichosurus vulpecula. While many marsupial introductions have failed, marsupials as a group were the first mammals known to have been translocated by humans (Heinsohn 2010), and Brush-tail Possums are causing major changes to New Zealand ecosystems (Montague 2000). Thus the introduction of a different species of possum to an island that lacked non-volant mammals until the arrival of people could have inter-generational consequences. Second, New Zealand now hosts not only Brushtail Possums, but a range of highly effective introduced predators including stoats. Mustela ermine which are absent from Australia and could reduce the chances of successfully establishing the pygmy-possum, and provide a new source of stress for the animal. Third, Bogong Moths do migrate regularly to New Zealand, and will breed there, but the moth larvae currently fail to survive New Zealand winters (Fox 1978). From a practical point of view, the regular survival of Bogong Moth larvae as a result of global warming, and the establishment of the species as a New Zealand resident, could be seen as the trigger to initiate introduction of the pygmy-possum.

It is clear that there are the elements here to seriously consider the AC of the Mountain Pygmy-Possum. We have an endangered species whose habitat is shrinking because of global warming. They cannot go any higher in Australian alpine ecosystems and New Zealand has much higher mountains. While New Zealand might not be an ideal relocation proposal, the issues of cultural acceptance of a new possum species and threats from predators are not insurmountable. The acceptance by traditional owners of new species in emergent hybrid eco-cultural environments has been discussed by Albrecht et al. (2009) in the context of Northern Australia and the introduced Asian Swamp Buffalo (Bubalus bubalis). Unlike buffalo, Mountain Pygmy-Possums are small (mouse sized), arguably ‘‘cute’’ and offer none of the threats of the larger Brush-tail Possum and they therefore could be incorporated into contemporary New Zealand culture without controversy.

New Zealanders just might be quick to embrace the new little possum into their land, especially if the reason for its introduction is to save it from extinction. The beauty of the animal and the fact that it is harmless to humans all work in its favor. The predatory stoats are a serious issue but controlling them is not in principle any different to controlling feral cats (another very effective predator) or foxes. The control of such introduced predators is necessary in any case for New Zealand birds (for example, the flightless Kiwi) and something with which New Zealand conservation managers have decades of experience. The issue with the Bogong moths could be a bonus for Mountain Pygmy-Possum in New Zealand, one that could see symbiosis between the two species re-emerge in a new location favorable to both. The essential elements of the intrinsically valuable mountain ecosystem of Eastern Australia are then replicated in a New Zealand location and the intrinsically valuable species of the (former) Australian context can continue their evolutionary trajectories and are saved from extinction. There seems to be no potential for serious violation of either the interests of Mountain Pygmy Possums or a major threat to the host ecosystems over and above the risks presented by climate change itself. Mountain Pygmy-Possums have been successfully bred in captivity and their introduction to a number of new in-the-wild locations in both Australia and New Zealand would be an expression of a wise stewardship strategy of safety in diversity.

When an animal is already endangered and its original habitat is disappearing, the risks of possible harm have to be weighed up against the risk of extinction. As long as no net harm is caused to the parties involved in both Australia and New Zealand, there is an a priori case for AC in this case study. Finally, the Mountain Pygmy-Possum can be returned to Eastern Australia if and when the global climate is returned to one that permits its re-introduction to its former home.