On the hop
New Zealand does Australia a favour (10 minute read)
It’s a sight which is simultaneously familiar and bizarre. Across a broad sweep of grass in the grounds of the Sydney Botanical Garden at Mt Annan, a kangaroo bounces along. It is perfectly balanced on its powerful hind legs – as it leans forward, the weight of its body is countered by the weight of its outsized tail. I raise my camera, but I’m here to photograph plants, so I don’t have the right lens. The resulting photograph shows an attractive landscape with gum trees, and a couple of distant blobs with upright ears.
The kangaroo is a symbol of Australia, much as the kiwi is a symbol of New Zealand, perhaps more so. It appears in the logo of the national airline, the Commonwealth coat of arms and the names of sports teams. Well, technically, only the men’s rugby league team is known as the Kangaroos, but Australia also has the Jillaroos (women’s rugby league), Socceroos (men’s football), the Jackaroos (bowls) and a few other random names with aroo stuck on the end (like Boxaroos for box lacrosse, a sport I’ve never heard of).
As a nature-obsessed child, I could tell you all about kangaroos. I knew that they were mammals, like us, but that they were an unusual kind of mammal called a marsupial. Their babies were born tiny, naked and blind, and after being born they would drag themselves along a path which their mother had licked in her fur until they reached her pouch. There, they would latch on to a teat and remain attached for months.
I could tell you about other marsupials too – the wallaby, smaller than the kangaroo but with the same hopping habit, the koala, almost as iconic as the kangaroo, the wombat and, of course, the brushtailed possum. Most of what I knew about possums I learned from a book called Sparkles the Cuddly Possum, a title which was acceptable in New Zealand in the early 1980s, but wouldn’t be published here today.
As an adult, what I know about marsupials is coloured by their role as pests in New Zealand. I don’t think I’m overstating it when I say that the possum has been an utter disaster. Its value as a source of fur is vastly outweighed by the the destruction it brings to native plants and animals. Cute as it is, I wish we could send every one back to Australia, but the possums here carry bovine tuberculosis, so Australia doesn’t want them.
What Australia did want from us, however, were our wallabies. George Grey, a much-venerated colonial governor whose ideas are not judged favourably by history1, decided to introduce five species of wallaby to his private island in the 1870s. They thrived there and two species were also introduced to other parts of the North Island. These have become pests, both for agriculture and the environment, since they eat grasses as well as native trees and shrubs. A further species, which was released in the South Island, has also become a pest.
I’m so used to Australia’s marsupials being a problem in New Zealand, that I’ve never thought about them as under threat at home. In fact, many of Australia’s unique mammals are not doing well. Since European arrival, 39 species have become extinct, and another 110 are threatened. This means that around a quarter of Australia’s mammal species, most of which are found nowhere else, are in trouble. While this isn’t as dire as New Zealand’s birds, it’s still a woeful situation.
The kangaroos I saw at Mt Annan were probably eastern grey kangaroos, one of more than 40 species in the broad group which includes kangaroos, wallabies and various smaller species such as pademelons and potoroos. Eastern greys, along with red kangaroos, are doing well – in New South Wales alone there are millions of them. The total number fluctuates considerably, largely in response to drought. In the Tibooburra area of New South Wales, where kangaroos have been closely monitored, there were around 1.5 million in 1998, only 360,000 in 2006 and 1.5 million again in 2016. They are commercially hunted for meat and fur, as well as being culled in some areas when they compete with livestock for food. There’s some debate about the impact this has and whether it's sustainable, but there are still good numbers of them in some areas.
This doesn’t mean that they are doing well everywhere. Places like south-eastern Queensland are seeing large increases in the human population, and that is leading to declines in kangaroo numbers. Still, kangaroos are doing well compared to some of their smaller relatives. The most endangered is also the smallest, the Gilbert’s potoroo, which was once common on the south-west coast of Australia. Today there are fewer than 200 left. Also in desperate trouble is the woylie, another small species once found throughout most of Australia, but today found only in a few, isolated places. Larger species, such as the brush-tailed rock wallaby, are also in trouble. Even species not strictly classed as threatened, such as the tammar or dama wallaby, have suffered substantial declines.
In New Zealand, threats to our native animals can be summarised in two words: introduced mammals. There are other factors, such as a loss of habitat and disease, but today these threats are secondary to the onslaught of rats, stoats, ferrets, weasels, possums and cats (not to mention pigs, goats, deer and, yes, wallabies, which affect the habitat). In Australia, though, things are more complicated.
Australia had, and still has, native predatory mammals, such as several species of quoll and the now-extinct thylacine. Dingoes aren’t native, but they were introduced several thousand years ago, so it’s likely that any species which couldn’t co-exist with them became extinct long ago. As a result, Australia’s native mammals haven’t proven quite so vulnerable to predators such as rats (and, as far as I can tell, nobody had the terrible idea to introduce stoats, ferrets and weasels there). However, they do have a serious problem with feral cats, as well as stray and pet cats, which do serious harm to native wildlife. They also have one other predator which New Zealand has been lucky to avoid – the fox. It was introduced in the 1850s, and was out of control within a couple of decades. Now, it is found across 75% of Australia.
In the late 1980s, biologists observed that the most endangered of Australia’s animals, at least the non-flying species, fell within a specific size range, from 35g to 5.5 kg. Admittedly, this is a wide range, but it is notable because it is counter to what is observed elsewhere: the larger the animal is, the more likely that it will be endangered. There are a number of ideas for why this should be, but the impact of foxes and cats is central. Larger species are too big for foxes and cats to kill, while the smallest species are either too small or have shorter life cycles, which allows the population to recover.
The species most vulnerable to foxes and cats can be protected on islands and predator-fenced mainland sanctuaries. These have been successful in helping a number of species survive and even increase in numbers. One example is the burrowing bettong, a relative of the kangaroo which falls well within the critical weight range for vulnerability. It was once one of the most widespread Australian mammals, but by the 1960s was confined to a few offshore islands. However, it has since been reintroduced to a number of fenced mainland sanctuaries.
However, there are other threats to Australian mammals as well. The brush-tailed rock wallaby, for example, was extensively hunted for its pelt. In a single year, one company sold 100,000 skins. Today, there are fewer than 30,000, and most of these are of the more northern form. Populations from central New South Wales and Victoria are almost extinct.
The rock wallaby is now protected from hunting (as far as I can tell – Australian legislation is much less user-friendly than New Zealand’s). It is at the upper edge of the size range vulnerable to foxes and cats, meaning that younger animals are vulnerable but adults less so. However, there are still many other threats. It does best in relatively undisturbed habitats, but much of the area where it used to occur has been changed in various ways. Forest has been cleared, exotic plants have invaded, fire patterns have changed in complex ways – to what indigenous Australians call ‘wrong-way’ fires – and livestock have grazed. Another problem facing species such as the rock wallaby is that the remaining individuals occur in small, fragmented groups. This can result in inbreeding, making the groups vulnerable to genetic defects and disease.
Another species with a complex range of threats is the tammar or dama wallaby. It is secure on islands such as Kangaroo Island, south-west of Adelaide, and has been introduced to other offshore islands. However, it was wiped out on the mainland by the 1930s, by a combination of hunting, land clearance and foxes – like the rock wallaby, it is at the upper edge of the vulnerable weight range. There are differing opinions on whether all the wallabies under the name tammar wallaby are really the same, however some sources consider the Western and South Australian forms to be different, and the Kangaroo Island and mainland forms to be different.
But there’s one place where both tammar and rock wallabies thrived. You guessed it – New Zealand. Both species survived on George Grey’s private island, Kawau, with rock wallabies also thriving on Rangitoto-Motutapu, and tammar wallabies doing rather too well around Rotorua.
Rangitoto-Motutapu, however, are important islands for the conservation of native plants and animals. The New Zealand Department of Conservation wanted to eradicate the introduced mammals, including the wallabies. Before that happened, though, a number of the endangered wallabies were sent back to where they’d come from. These were used to establish captive populations in places such as the Tidbinbilla Nature Reserve near Canberra and Taronga Zoo in Sydney.
But when Australians realised that our tammar wallabies had come from the South Australian mainland, they really took notice. Since tammar wallabies had been wiped out from the South Australian mainland by the 1930s, the wallabies in New Zealand were something rare and precious. Even if they weren’t a different subspecies, as some biologists thought, they could contain genes which may have been lost.
In 2003, there was a special homecoming, as tammar wallabies travelled from New Zealand to South Australia. After a few months in quarantine, they were released in the Dhilba Guuranda-Innes National Park on the Yorke Peninsula, near Adelaide. Although not all of the reintroduced wallabies survived, today the population there is increasing.
The plants and animals of Australia and New Zealand have a complicated relationship. They have been separated for 85 million years, but in the last 200, we have been moving species back and forth across the Tasman Sea. For some species, that has made little difference. The pūteketeke made famous by John Oliver and the mānuka tree are common to both. Sometimes, the species either side of the Tasman Sea are cousins, like New Zealand’s kauri, which has close relatives in Queensland, and is also related to the Wollemi pine. Sometimes, as with the possum, it has been a disaster. Although nothing which has gone in the other direction has been quite so terrible, some of New Zealand’s lovely ornamental sedges have proved a problem in Australia.
And then there are the wallabies, where New Zealand was able to do Australia a favour and send some of them back where they came from.
When it comes to invasive species, nothing is ever black and white. No species is good or bad. I don’t believe that we should allow our native species to be driven to extinction by species such as the possum or rat, or even an endangered wallaby. I support efforts to control species such as possums, stoats and rats in New Zealand. But nor do I think it’s necessary to demonise a species, even if it is harmful. They are simply in the right place or the wrong place, depending on what we deem important.
When Grey was in Australia in 1840, he proposed that indigenous children be educated in boarding schools so that they could be swiftly assimilated. Colonial administrators loved the idea so much that it was subsequently introduced in a number of English colonies around the world, to devastating effect.
As usual. Fascinating. David Farrier wrote about opossums today also.