Introduced Wild Animals in Australia

Introduction

There are now many animals living in Australia that have been deliberately introduced to the wild. Some came by accident, others were escapees from aviaries, aquaria and zoos. They were introduced for a number of reasons that now may sound quaint or impractical. It is a good history lesson to examine past introductions so that the same mistakes are not repeated in the future.

When populations of domestic animals such as livestock or household pets become established in the wild they are called feral animals. These include the feral cats, feral pigs, the hare, feral goats, and feral horse or brumby. However, the introduced species that did not originate from domestic livestock are referred to as exotics, exotic wild animals or introduced wild animals. Here are some reasons why these wild animals from other countries were introduced into Australia and just a few example of the species involved:

Sport hunting - rabbit, fox, deer

Fishing - trout, carp

Practical use - ostrich, camel, buffalo

Ornamental - blackbird, song thrush

Accidental - two species of rat, house mouse, European wasp, cattle tick

Escapees - Indian Palm squirrel, goldfinch.

The introduced wild animals have had a great impact on the Australian environment and the productivity of many of its agricultural industries. The full impact of many species is still to be determined but sufficient is known to warn against any further uncontrolled introductions for the following reasons:

Disease and parasites - these usually are introduced accidentally such as the cattle tick that came with cattle or goldfish ulcer disease which was introduced through the aquarium trade and spread to wild stocks.

Pests - introduced animal pests now affect almost every aspect of the national economy and the community. There are the obvious pests to agriculture such as the European wild rabbit, the house mouse and the starling. Many of the birds and particularly the rodents, are serious pests in towns and cities.

The brown hare

Early attempts to establish wild populations of the brown hare Lepus capensis in Australia failed. The hare is now common through a wide belt of eastern Australia extending from central Queensland into South Australia. It spread from a colony established on the shores of Westernport Bay, Victoria in 1862. This was only a few years after the introduction of the wild rabbit but the hare has not spread as far as the rabbit or caused the same amount of damage. However, the hare can be a problem where farmers are trying to regenerate native vegetation or undertaking tree planting programs because it eats young trees seedlings. The hare does not burrow or reproduce as rapidly as the rabbit can be more easily controlled by shooting. It is not vulnerable to myxomatosis.

The European red fox

The European red fox Vulpes vulpes was released near Melbourne in 1845 for sport hunting. It spread rapidly and took only 50 years to cross the Nullabor into Western Australia. The fox is now found on most of the mainland except in the far tropical northern regions. It is not known whether climate or higher concentrations of dingoes have limited the spread of the fox into this region. The fox has not established in Tasmania but together with the feral cat and the house mouse it is one of the three most widely distributed introduced wild animals in Australia.

It was believed that the only serious problem caused by the fox was that it preyed on lambs and goat kids. However, there is now evidence the fox is causing the decline of certain species of Australian wildlife. The smaller ground-dwelling native mammals are particularly vulnerable when their habitat has been reduced by disturbance such as land clearing for agriculture. Predation by foxes can tip the balance between survival and extinction for species such as the numbat and the black-flanked rock-wallaby. Consistent fox control on nature reserves in Western Australia in recent years has resulted in dramatic recoveries of populations of small native mammals such as the numbat.

The fox is also a potential carrier of rabies should it enter Australia. This disease primarily affects members of the dog family but can also be transmitted to humans, livestock and native birds and mammals. Rabies occurs in most parts of the world and is prevalent in South-East Asia and Indonesia. There is a serious risk it could enter Australia through the illegal importation of an infected dog. Wherever rabies has become established it has persisted despite all attempts to eradicate it.

The main forms of fox control are shooting and poisoning. A combination of both has proved successful in and around nature reserves in Western Australia but there is an enormous cost in maintaining such a program. In the past, commercial shooting of foxes for fur was a viable industry. This has changed since furs are out of fashion and the market value of fox skins is unstable. As with the rabbit, one hope for fox control lies in genetic engineering techniques that will induce infertility.

Deer

Wealthy colonists dreamed of being able to live the life of European nobility in the land they left behind on the other side of the world. They worked hard to make their dream a reality by establishing wild populations of deer to hunt. Dr John Harris of Sydney imported the first deer into Australia in 1803. They were chital deer from India and were running wild a few years later with strenuous efforts being made to protect them from poachers and dogs.

These first wild deer in Australia were seen as a great success and a further five species of deer from different parts of the world were eventually established in the wild. They were fallow deer, red deer, sambar, rusa deer, chital and hog deer. However, none of them have become widely distributed. Each species has a different and fairly narrow set of requirements so that they are now found in widely varying climatic regions in small pockets of favourable habitat.

Only the sambar, found in the forested ranges of Victoria through to south-eastern New South Wales, could be regarded as having the potential to increase its range. However, hunting appears to prevent this deer from becoming a pest. Consequently, no species of deer is regarded as a serious pest and since their numbers are limited by environmental factors such as climate, cover and food supply, they are more likely to be viewed as a recreational resource. Farming deer for venison and antler velvet is a growing industry with approximately 100 000 deer on farms in Australia.

Rodents

The house mouse, the black rat and the brown rat probably came in the holds and with the cargo of the First Fleet but they could also have arrived with earlier seafarers that visited Australia's northern coastline. These rodents benefit from human habitation and the changes brought about by crops and horticultural practices. Both the black rat Rattus rattus and the house mouse Mus domesticus colonise natural areas with the rat implicated in damage to seabird colonies on offshore islands.

Modern hygiene has broken the link between rats and bubonic plague - the disease carried by the black rat that affected humans so disastrously in the past. However there is still reason to be concerned about the ability of this species to spread leptospirosis and cause salmonella poisoning. Other problems caused by the black rat include damage to insulation covering electric conductors by chewing, and the increased fire risk and cost of repair involved.

The house mouse reaches plague proportions in the wheat belt regions when soil moisture conditions that allow easy burrowing coincide with abundant ripening grain. The plagues cause economic damage to cereal crops and oil crops such as soya bean. They are also a nuisance in houses. There is no effective control of mouse plagues. Research into biological control and improved methods of poisoning is proceeding.

Birds

In the past, many different groups devoted their energies to introducing any bird that might have been `useful'. The prevailing concept of usefulness covered the ornamental, sentimental and pragmatic. Birds were easy to obtain, relatively easy to transport and could be nurtured in aviaries before release in to the wild. For example, the house sparrow was introduced to alleviate the pangs of homesickness felt by those so far away from the familiar species of the Old World. It is now regarded as a pest because of its habit of nesting under roofs and fouling buildings with its nesting material.

The European goldfinch, now found in the farmlands of south-eastern Australia, was introduced as an ornamental addition to our avian fauna. The ostrich was introduced for its feather and meat and there is still a small wild population in South Australia. Other introductions for practical reasons, such as biological control of insects and farm pests, were all outstanding failures and merely resulted in another pest. The common starling is undoubtedly the best example of such a species. Apart from being a major agricultural pest is competes with native birds for nest sites such as tree hollows.

Another species which is believed to compete with native species is the nutmeg mannikin which was introduced from China as an Aviary bird but became established in the wild after escaping in Brisbane in the 1930s. It is now common in many parts of coastal Queensland and is rapidly extending its range.

There are now as many as 20 introduced species of birds living in the wild in Australia. Introductions are not a thing of the past. There are continuing efforts, both legal and illegal, to bring new birds into Australia. Most are for cage birds but given the past record of the potential for escapees to become established in the wild it is essential that extreme caution is applied when evaluating the risks of more unwanted additions to the bird fauna of Australia.

The Cane Toad

The outward appearance of the cane toad is living proof that good looks are not the only road to fame. This animal, introduced in 1935 to control two insect pests of sugar cane, has achieved a great deal of notoriety and publicity. One reason for this is its characteristic warty appearance and poisonous glands. The other reason is that its introduction as an agent of biological control was a failure. Both the insect pests and the cane toad continued to thrive.

The cane toad now occupies a range of over 500 000 square kilometres. It has been able to spread through a combination of natural advantages. It has a strong body covered with a tough skin and can live up to 15-20 years. Females can lay up to 30 000 eggs per year while Australian native frogs usually lay less than 1000 eggs per year.

In addition to such breeding efficiency, the cane toad is poisonous to native predators. The large glands protruding from its shoulders exude a creamy white toxin. Frog-eating reptiles have been seen to die after only grasping a cane toad between the jaws before rejecting it. There is no reliable safe method of reducing the cane toad population over the extensive areas of northern Australia where it occurs. A search for a disease that is specific to the cane toad is currently being undertaken by the CSIRO.

Fishes

The best known species of introduced fish are probably the brown trout and rainbow trout. They were introduced during the latter part of the last century when people craved a wider range of sporting fish. Trout have thrived in the cooler streams of south- eastern Australia and the extent to which they have changed the abundance and distribution of native species is still poorly understood. However, research in Tasmania strongly implicates the brown trout in the decline, almost to extinction, of native fish, the Lake Pedder Galaxia.

Five species of carp were also introduced to enhance the sporting and aesthetic qualities of Australian waterways. The common carp is the most widely distributed and is regarded as the worst pest. It is also possible that land degradation, through soil erosion and salinity and pollution, has had the greatest impact on reducing the stocks of native fish. The common carp has thrived under such conditions.

The mosquitofish was introduced to Australia from the Gulf of Mexico drainage system. It was released in Sydney in 1925 and Brisbane in 1929 to control mosquito larvae in dams. This fish has had a certain success in mosquito control but evidence is mounting that it also has a detrimental effect on native aquatic fauna. The mosquitofish attacks native fish and causes substantial damage to their fins as well as aggressively competing with them for food. It has caused the decline of a native fish on Stradbroke Island, Queensland.

Insects and molluscs

Most of the well known pests such as the garden snail, the fruit fly and the cattle tick found their way here by mistake and have become a great cost to Australian society. These accidental introductions are still occurring, with one of the best known recent examples being the arrival of the European wasp.

A queen wasp probably hibernated among cargo on a ship in New Zealand where it had also become established and was carried here to start the Australian population.

The honeybee was deliberately introduced but soon became established in the wild. The requirements of the honeybee for nectar overlap with numerous native species, and there is now concern that this exotic species is having a greater impact than previously thought. There is evidence that the honeybee is a more efficient forager than native pollinators and therefore competes with them for food. However, it is a less efficient pollinator than the native animals that have evolved with the Australian flora. This means that if the native pollinators are forced out by competition for food then some native plants may remain unpollinated and fail to reproduce.

Conclusion

With the great wave of animal introductions that followed Europeans into Australia came many species that we could now do without. There was either no concern or no system for identifying the truly useful from the truly troublesome. Consequently, there were many unforseen results from introducing a host of new animal species into Australia without considering what impact they might have.

Unscrupulous collectors still attempt to smuggle birds, reptiles and fish into Australia that can carry disease or become established in the wild if they escape or their owners tire of keeping them. With the greater reliance on world trade in increased overseas travel, the opportunities for the accidental introduction of new species has increased rather than diminished.

The major exotic animal pests now cost Australia many millions of dollars annually and this is why continued quarantine vigilance is essential. The main method of preventing further entry of undesirable exotic animals is to prevent the importation of all plants and animals without proper quarantine and thorough biological screening procedures. The great challenge is to balance the desire to import new species with the risk of them becoming pests.

Australia now has the knowledge and experience to make an even greater effort to protect its native plants and animals and primary industries so vulnerable to introduced pests. If we have learnt anything from the past then it is the need for constant vigilance. However, the task can not be left to governments alone. A responsible and caring public is essential. Everyone eventually pays for the damage caused when introduced animals arrive in Australia where they are neither needed or wanted, only to become a pest.

There are few cases of introduced wild animals that are not controversial or without problems today. Even those species that are considered desirable by some sectors of the community, such as trout, cause concern and their impact is still be to be fully determined. A commercial use has been found for some of the introduced species such as the rabbit and this serves to complicate their management because they are both a pest and a resource. However, for the great majority of introduced wild animals in Australia there is the wish that we could turn back the hands of time and assess the costs and benefits in the light of current knowledge.