Eastern states experiences

Survival, drey use, bushfire

For more information see:  Augee et al, 1996, Russell et al, 2003

Survival of relocated ringtail possums is low no matter whether it is the western or the common species. The cause of high mortality is usually predation.
In a study on common ringtails between 1990 and 1994 52% possums were killed by foxes and 29% by cats. Of 118 individuals whose fates were determined – wild caught and radio-collared and relocated animals - only 8 were not killed by predators.

Interestingly, relocated ringtails survived an average of 101 days, while wild residents survived an average of 182 days.  In the early stages of the study introduced possums were at a clear disadvantage compared to residents and much more rapidly taken by predators.
Also interestingly, there was no significant difference between animals that were hand-reared and those that were merely relocated. The high vulnerability to predators was therefore not due to their ‘unnatural’ upbringing but the result of relocation into unfamiliar territory and maybe competition with established, wild ringtails, but the latter was not investigated.
In the long term resident ringtails were just as heavily predated upon as the relocated animals. 

One wonders how the eastern species can still be common if they are predated at such an extreme rate but in this particular case factors related to the actual study could have contributed to the bad survival rate. Firstly, in the group of wild-caught animals were more mature, heavier animals and the better body condition could have increased their survival time.
For at least 3 days the ringtails were kept in a large outdoor aviary with natural food supply so that they could get used to the radio-collar. However in those early days the slightest animals had to carry a collar that weighed 9.2% of their body weight and even the largest animal was still over the acceptance range of 2.08% which was established by Kaori Yokochi (Yokochi, 2015). According to her the heavy collar will have lowered the survival changes significantly. The high and early mortality might therefore have been a human artefact.

The same study also investigated the use of artificial dreys after translocation. Unfortunately no specifics were given regarding the design and measurements of the dreys.
The animals were taken to the release site in an artificial drey that was then tied to a tree. Those dreys kept being used occasionally by radio-collared animals, in some cases for many months, and were only removed when they deteriorated beyond usability. No information is given whether wild ringtails also used those artificial structures.
However in average only 1 in 15 monitored dreys was occupied when checked. The dreys were also used by brushtail possums and by rats. 
Common ringtails similar to our western ringtails have several dreys at any time, they re-use dreys over at times long periods, and they might be used by various possums over the lifetime of a drey.

All ringtails, wild and relocated, showed a clear preference for dreys – 63.1% compared to 29.5% that rested in tree hollows and 7.4% in nests near the ground. However those figures might just reflect the opportunities in this specific habitat.

A bushfire ended this 4-year study of ringtails as 7 out of the remaining 12 were killed in it. The survivors moved to the edges of the burnt National Park but all were taken by predators in the following 2 months – 3 by foxes, 2 by cats.
Surveys over the next 4 years of the affected area never recorded more than 2 ringtail sightings. To counteract the lack of recovery, 22 animals from rehabilitators were released in the area in 1998 but they only survived an average of 38 days due to heavy predation - this time also by native predators such as pythons and lace monitors. Again, the animals carried far too heavy (according to new research) radio-collars, mortality in summer was particularly high and the habitat and in particular the myrtaceous understorey had obviously not recovered sufficiently enough. The simpler vegetation structure and the isolation of possums in certain spots clearly made hunting for cats and foxes easy.

Even though the fire destroyed old hollow-bearing trees, nesting behaviour shifted towards the use of hollows as there was hardly any material left for drey building.
The main advantage of hollows is more effective insulation during hot weather. However the combination of decreased density and continuation of canopy and less understorey vegetation the increased use of hollows instead of dreys led to increased python predation.

release methods