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Enter: Europeans, cats and foxes


 
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Professor Chris Johnson, from James Cook University, continues his series on mammal extinctions, this time concentrating on the second wave of extinctions coinciding with European settlement.     
The Thylacine was already extinct on the mainland and on Tasmania, followed suit soon after the arrival there of Europeans. While some theorise that a cat-borne disease such a toxoplasmosis wiped them out, Professor Johnson believes that over hunting is much more likely.

The first bounties for Thylacines were introduced around 1830, usually given to pastoral companies to protect their flocks of sheep. A noisy lobby of sheep graziers, however, persuaded the Tasmanian government to introduce bounties across the state, killing both adults and increasingly juveniles, a clear sign that the Thylacine population was being depleted.

Thylacines were effectively extinct by 1905 with the last one dying in 1930. Ironically, the extinction of the Thylacine had little effect on the kill rate of sheep in Tasmania since feral dogs were their main predators, but as a scapegoat, the Thylacine was made to suffer.

 
On the mainland another form of extinction was happening, this time from introduced predators. It seemed to be a selective pattern of extinction, that centred on medium sized mammals like the Desert rat kangaroo and Hare-wallabies.    
These mammals lived in the drier parts of southern and central Australia, often in places where there was no contact with Europeans and the extinctions usually occurred in waves.

These waves have been reconstructed in NSW, where the extinction of the Rat kangaroo can be traced to an introduced mammal – the fox. As the colonisation of the foxes moved from south to north, populations of Rat kangaroo were typically wiped out some five to ten years later.

 

Left: Figure 11.4 page 199 of Australia's Mammal Extinctions (based on Short 1998).

The figure shows the relationship between increasing fox numbers (shown as dashed lines) and the decline in rat-kangaroo populations (solid lines) in southern (a), central (b) and northern (c) NSW.

The vertical arrows indicate the introduction of foxes to each region.

Fox numbers estimated by multiplying the annual number of bounty payments by five.


 
Cats were also a problem and had rapidly colonised virtually the entire continent.    
One feral cat can kill as many as 20 Hare-wallabies in a couple of days and while population of rabbits can survive these rates of predation, the Australian marsupials with their lower reproduction rates cannot. Interestingly, cats were found to be less of a threat to native species in the arid central and north western regions of the continent. Their numbers were controlled because the Aborigines hunted cats, which were easy prey for them in the open. Unfortunately, the arrival of Euriopeans resulted in many Indigenous communities being taken away from their lands and once the Aborigines left, cats quickly established themselves as the top predator leading to the extinction of a range of medium sized marsupials.

 

    
Right: Plate 34 from Australia's Mammal Extinctions.

Photograph by Ken Johnson of a captive Mala (rufous hare-wallaby.

The species was wiped out on the Australian mainland in 1991 and remaining populations only survive on islands off WA and in captive colonies.

So far attempts to reintroduce the species to its mainland habitats have failed because of predation by feral cats.

 
The only places where cats and foxes are kept in check are those that have a dingo presence.    
Adam O’Neill, a feral animal exterminator and author of the book Living with the Dingo, believes that the dingo has a huge impact on the biological control of feral animals and that the dingo could help re-establish native mammals across northern Australia. The dingo as top predator, serves as a controlling factor in the same way that has been observed for top predators in other countries. Top predators have a large effect on the abundance and behaviour of smaller predators, especially as they will maliciously hunt other predators to maintain their competitive edge. In turn, this protects many of the prey species of these lower order predators. For example, where wolves and coyotes are found in North America, foxes and cats are less abundant and song bird numbers are maintained.

Australia has the world’s worst record for recent mammal extinctions and given that we have lost most of the 20 species over the last 200 years, certainly not a world record that conjures up any pride.

Text: V.B. December 2008

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50,000 years of mammal extinctions Very different hazards but often similar issues for community preparation and recovery

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