By Andrew Luck-Baker
Producer, Discovery programme, BBC World Service
Cross-fostering could help save species from extinction
Australian scientists are kidnapping babies from the pouches of endangered marsupial mothers in a bid to save their species from imminent extinction.
They fly the tiny, helpless wallaby babies out of their remote mountainous homeland by light aircraft and transfer them into the pouches of surrogate mothers of another common species, held in captivity. Here the poached young are raised to adulthood in safety.
The dramatic technique has been developed by scientists working at Adelaide Zoo and the University of Adelaide, who say it can boost the reproduction rate of endangered marsupials by as much as nine times.
The method exploits unusual aspects of marsupial reproductive biology.
The researchers have begun to re-introduce highly threatened wallabies bred this way into the wild and are optimistic that they can bring the animals back from the brink of extinction.
According to lead researcher David Taggart, the state of Australia's fauna demands drastic measures. He says that 40% of the country's animal species are deemed to be endangered or vulnerable to extinction.
Australia's tally of extinctions over the last 200 years is the worst of all the world's developed countries. Habitat destruction and the impact of introduced foreign creatures such as domestic cats and red foxes are the primary reasons.
One of the marsupial species closest to extinction is the brush tailed rock wallaby. It clings to existence on the cliffs and crags in parts of the Great Dividing Range in the east of the country. Its wild population is estimated to number in a few tens.
The brush tailed rock wallaby was the first species to be targeted for preservation using the pouch-swap technique, which is more properly known as cross species fostering.
The surrogate mums belong to a species of which they are plenty. One of those is the yellow foot rock wallaby which inhabits arid areas of southern Australia. They are housed in captive colonies on the outskirts of Adelaide.
The pouch young come from two sources. At the captive facility, there is also a small breeding population of the endangered brush tailed species.
After a brush tailed mother has given birth to her tiny joey and it has begun to suckle in her pouch, in come the scientists.
They tranquilise her and carefully transfer her baby into the pouch of a surrogate yellow foot mother, where it will happily thrive and grow.
Then the unusual aspect of marsupial reproductive biology comes into play. The robbed mother quickly replaces the missing joey with a new one.
Wallaby and kangeroo mothers always have a spare in a state of suspended early development in their wombs. It is a reproductive insurance policy.
Within a month of the joey-napping act, the ready-to-go embryo has been born as a baby and set up home in mum's pouch.
Brush tailed rock wallabies could breed in greater numbers
With a well supervised breeding schedule combined with the cross fostering, David Taggart says they can produce new brush tailed rock wallabies in much greater numbers than relying on Nature.
"Instead of them producing one young a year, using this technique we can get eight or nine pouch young produced by every female every year. So it has a dramatic effect on the breeding rate of that species."
However, to prevent the growing captive cross-fostered Brush Tailed population in captivity from becoming inbred, David Taggart also goes on expeditions to the few remaining areas where the endangered rock wallabies still survive.
He needs some new joeys from the wild to increase the genetic diversity. Speaking to the BBC World Service science programme Discovery, David Taggart explained how it is done.
"We can go out along the Snow River gorge in Eastern Victoria and trap a female with a tiny pouch young.
"We harvest the young, put it in an incubator, hike it out of the gorge, jump in a light plane, fly a distance of 1000 kilometres to Adelaide and bring it across to where we have a captive population of a suitable surrogate species and transfer it into the pouch of a surrogate mother."
Back in the wild, the bereft brush tail mother replaces her lost joey with another in short order. However there is one loser in the procedure. A joey can only be cross-fostered to a surrogate yellow foot mother who is producing milk.
That means her own pouch young has to be removed and sacrificed in the cause of saving the more endangered species.
Joeys reared by the surrogate mothers do not appear to suffer identity crises once they have left the pouch. David Taggart says that most of their behaviour is hard-wired. So they behave like brush tails and mate with them rather than trying to get amorous with yellow foots.
Although the wild re-introductions of cross-fostered adults have only started in the fifteen months, the signs of sustainable success are so far are encouraging. Two sets of brush tailed rock wallabies have been given their freedom in the Grampians National Park in the state of Victoria.
Many attempts by zoos to re-introduce captive-bred creatures into their natural habitats have ended in failure. Often this is because too little was known about the animals' natural behaviour and ecological needs.
Also the problems in the environment that pushed the species toward extinction in the first place were not adequately addressed.
In the case of the cross fostered wallaby project, David Taggart says that long term success depends on a sustained programme of removing the feral cats and red foxes with baited poison, and concerted efforts to reduce the wildfire risk in their habitat.
Discovery - What's the Point of Zoos? is broadcast on BBC World Service on Wednesday 17th February. The programme is a co-production between BBC World Service and ABC Radio National