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Originating from Australia, the brushtail possum arrived with the sole purpose of providing a thriving fur trade but instead catalysed an ecological crisis. Now, their adaptability and opportunistic nature pose a formidable threat to New Zealand wildlife like the kiwi. Here, we delve into the brushtail possum’s characteristics, their impacts on NZ’s environment and wildlife, and the ongoing efforts to mitigate the possum invasion and safeguard New Zealand's precious biodiversity.
Characteristics and Lifestyle
The brushtail possum is a marsupial, a mammal that gives birth to underdeveloped babies that continue the rest of their growing attached to their mother drinking milk, usually inside a pouch. Australia is a marsupial kingdom, home to two-thirds of the world’s marsupials, around 250 species. It’s where you’ll find kangaroos, koalas, wombats, and over 30 possum species, including the brushtail possum.
While considered a havoc-wreaking furry fiend in New Zealand, the brushtail possum is an important ecological species in Australia. As primarily an arboreal folivore - a tree-dwelling animal that eats plant material - it helps maintain ecological balance in its native forest ecosystems.
It feeds on blossoms and fruit, dispersing seeds through its droppings, and it helps protect gum trees by feeding on mistletoe, a parasitic plant that can harm gum trees if not controlled.
While thriving in New Zealand, and a primary cause of the kiwi’s never-ending battle for survival, brushtail possum populations are declining in some areas of Australia and are protected by law.
The Best of Intentions
In 1837, the first shipment of Brushtail possums arrived in New Zealand and was released in the South Island. With fur of superior warmth and phenomenal softness, early European settlers believed possums could provide New Zealand with a successful commercial fur trade.
By 1858, possums had successfully established themselves in New Zealand, and Initially, were protected by law to allow increasing numbers for the fur trade.
There were 36 batches of possums imported and released into New Zealand between 1858 and around 1921. By 1921, it was evident that the possums were surviving a little too well here, and the government prohibited further releases.
By 1946 all possum protection was lifted and brushtail possums were officially declared a noxious pest. Actions intended to launch a fur trade had, instead, launched an animal invasion.
How Possums Survived and Thrived
So how did the possum manage to take over New Zealand’s forests? Not all animals can cope with being thrown into a different environment, but brushtail possums can adapt, and they can adapt quickly.
Resilient and Versatile
Their adaptability is evident in many of Australia’s suburban areas where, even with declining populations, no matter where you are, even if you can’t see them, somewhere, somehow, there’s probably a possum. In these areas, they live most of their lives hanging about in the available suburban trees, just above people’s heads, and a lot of the time, under their roofs.
In Australia, possums face natural predators, such as dingoes and pythons, but their primary threat leading to population declines is habitat modification for human habitation. So how do the possums cope? They move in. With reduced forest availability, they find cosy cavities in roofs of human houses and settle in there. While feeding primarily on plant material in their natural environment, in the suburbs, they happily eat whatever they can get their little paws on.
Balancing Acts
When an animal is a natural part of a particular ecosystem, without human interference and modification, all the ecosystem components generally balance each other out. Populations are kept in check by their natural predators, parasites, diseases, and environmental pressures they have adapted to in that ecosystem over millions of years. When that balance is disrupted, things start to topple over.
Sometimes the disruption is minor enough that the balance only wavers and then stabilises again. Sometimes, you end up with ecological issues that are on the less severe end of the spectrum, such as possums not having enough habitat that they move to the suburbs and make homes in people’s roofs, and other times, the disruptions are catastrophic.
Perfect Pest, Perfect Predator
When possums reached New Zealand, they found themselves in areas of abundant forest habitat devoid of their natural predators. They began chomping through the trees and breeding quickly, reaching their peak NZ populations in the 1980s with an estimated 70 million possums. With booming populations, they were also competing for food sources, and as adaptable, opportunistic animals, they turned to native insects and animals, like kiwi, to bulk up their diets. While primarily eating plants in Australia, in NZ, they decimate every level of the forest ecosystem.
Destroying Forests
Every night, 50 million possums eat around 21,000 tonnes of vegetation or about 420 grams each. Not only do they feast on our native forest, but they also return night after night to a single tree, stripping it bare, before moving on to another of the same species. By doing this, they alter the overall structure and composition of New Zealand’s native forests.
Reducing Food Sources
By eating flowers and fruits, possums also deprive nectar-eating birds, such as bellbirds, tūī, and kākā of the crucial, high-energy food they need in important times of year, such as the breeding season.
Reducing Healthy Habitat
Native animals, like kiwi, have already had a lot of habitat reduced from human modification. With possums such huge contributors to changing forest structures, they reduce suitable habitat even more.
Possums also take over dens that kiwi use. Sometimes a possum simply being present in an area is enough to disrupt the kiwi’s natural behaviour, making it difficult for them to mate and breed.
Eating Native Wildlife
Possums scavenge birds' nests, feasting on eggs and chicks, and often kill adult birds too. Though some birds, like kiwi, can fight off possums once they’re adults, they can become exhausted having to do it all the time, especially as possums often visit the same nesting sites night after night.
How We’re Helping
Predator Free New Zealand Trust
Joining the possum on New Zealand’s most wanted list are its fur-clad companions: rats, weasels, ferrets, and stoats. In 2013, the Predator Free New Zealand Trust was formed with the mission to rid NZ of these five predators by 2050. The trust has been a major catalyst for action against introduced predators, encouraging, supporting, and connecting tourism operators, community groups, NGOs, and government departments throughout the country.
Trapping
Trapping takes place throughout the country and is the primary measure for supporting our native wildlife by reducing predator populations. Trapping is extensive in national parks, such as Fiordland National Park, as well as throughout farmlands. Many people also take part by setting up backyard traps as well.
There are also a variety of trapping initiatives to help boost trapping numbers, such as the Kepler Challange Mountain run, an annual community event in Te Anau that raises funds for predator trapping on the Kepler Track.
Predator Free Islands
Offshore Islands provide opportunities to eradicate predators from natural ecosystems using our current technology. These Islands provide homes for native species that can longer survive on the mainland with introduced predators. There are around 110 of these islands that are rich in biodiversity, providing a glimpse of what’s possible with predator eradication and habitat restoration.
1080 Poison
1080 is a highly effective, yet controversial poison used to help reduce predator numbers on a mass scale. Studies show that 1080 pellets break down rapidly in the environment and don’t contaminate water, but many people still worry. Additionally, some dogs have sadly died after eating poisoned animals like possums.
Though a rare occurrence, a small number of kea have also died from ingesting the pellets when interacting with bait stations, which is one crucial reason visitors must not feed kea when seeing them on trips to Milford Sound or elsewhere in NZ. Kea are highly intelligent and curious, and receiving food from humans encourages them to eat things they wouldn’t normally find in their habitat. Without 1080, we’d have a hard time reducing predator numbers, especially in areas humans can’t reach. It remains important as a means of predator control while the search continues for a silver bullet to protect our native wildlife like kiwi.
Ongoing Research
Research into large-scale 1080 alternatives is ongoing, and Otago Univsersity researchers recently mapped the genome of brushtail possums, uncovering important scent-creation genes.
As possums are nocturnal, they use many non-visual communication methods, such as scent trails. The researchers found genes that allow possums to carry scent in urine. They suggest that we could produce molecules from these genes and use them to lure possums into traps or keep them away from certain areas.
Fiordland’s Role
The Department of Conservation (DOC) is the primary government department responsible for the conservation of New Zealand's national parks, including Fiordland. As Fiordland is such a huge area to manage, many passionate tourism operators and community groups are active in conservation projects throughout the area. Examples include:
Kids Restore the Kepler
This conservation project aims to help youth develop leadership skills while helping manage environmental issues. The project involves activities such as water quality monitoring, habitat restoration, and pest control to help native wildlife in the Kepler area.
Tour Operator Involvement
Many tour operators contribute to conservation initiatives in the area. For example, Luxe Tours donates to the Kea Conservation Project. RealNZ also operates multiple conservation projects and activities including trapping, the Birds of a Feather Conservation Ball, Cruise for a Cause, and the restoration of Cooper Island.
Guest Levies
For every guest on guided tours, a levy is paid for the time people spend off the road on DOC land. These levy payments go towards conservation efforts in Fiordland.
How You Can Help Animals Like Kiwi
Buy Possum Fur Items
Possum fur items (hopefully) won’t be sustainable forever if we can eradicate possums from NZ. But we’re still a long way off, so in the meantime, you can buy possum fur clothing while you’re here.
“One of the best ways people can help is by buying possum fur items. It keeps you warm and encourages possum hunting and trapping” - Department of Conservation Educator, Queenstown.
Donations
There are many conservation efforts around, and the outcomes of supporting one will also lead to support for others since habitat restoration and predator control help all native wildlife. You can join Luxe by donating to the Kea Conservation Trust; Like kiwi, Kea are under attack by predators like the possum.
You can also donate directly to the Save the Kiwi Trust, and if you’d like something for yourself or a friend, purchase a children’s book, or T-shirt, or you can even make a donation to the trust in someone’s name.
The battle for New Zealand's unique flora and fauna wages on, but ongoing conservation efforts offer hope for the preservation of our precious species like kiwi. Through efforts like trapping, predator-free islands, research, and community projects and support, we’re helping defend them in their battle against predators like the possum, with the hope that one day, species like kiwi can thrive on the mainland once again.