Dispersal issues
Wide dispersal, particularly immediately after release, equals lower duration of survival according to translocation research (Clarke, 2011).
Released animals in this study tended to stay in the release area unless it was already fully taken up by resident possums. Some suddenly moved out of the release area they occupied for a while in response to for instance the loss of a partner. The habitat in this study is comparable to our sites and I would assume that the density was low due to reduced food availability and a new partner was therefore not readily available.
Travelling distances in this study were longer than expected - up to 9.5 km in total for one animal, and up to 2.5 km in 24 hours for another. These long distances are likely to be travelled mainly over the ground which would have increased the risk of predation significantly. (Clarke, 2011)
In another radio tracking study in Queensland, however with common brushtail possums, two thirds of the animals died during dispersal. (Spielman, 2008) Brushtail possums do not show similar canopy fidelity to ringtails possums and the predation risk for them is even higher. Even though translocated animals displayed some of the characteristics of naturally dispersing possums, wide dispersal was neither limited to young adults (sub-adults) nor to males. (Spielman, 2008)
During dispersal mortality in both species is generally high and relocation can be regarded as a form of forced dispersal unless the animals are released into empty, good quality habitat with an adequate carrying capacity.
If habitat is available in dispersal distance, those dispersals can still result in relocation success. Some of the western ringtail populations in areas such as Park Ridge, Myalup or near Mandurah (unconfirmed) may have been established as a result of dispersal from the translocation to Yalgorup National Park. (De Tores, 2009)
Similarly, our releases close to a national park might have led to or increased a population there. A map I received from the department indicating sightings have however underestimated the areas of occupation severely. Scat searches showed a wide distribution and some breeding home ranges.
As the habitat is sub-optimal – hardly any breeding/weaning grade habitat - and the animals have no access to (artificial) water sources, I would assume that the population is small and low density.
As our releases are not identifiable, their dispersal cannot be verified and the sizes of their home ranges are so far unknown.
A failure to acknowledge a certain (unquantifiable) mortality rate would suggest denial. However, without the use of radio telemetry even the most extensive monitoring effort would only be able to prove the presence and the persistence of a ringtail population, not its origins.
