Comparison of survival and reproduction of rehabilitated and uninjured koalas

 

Stina Magnusson and Chung Ping Woo

Wildlife ecology

 

 

Introduction

This essay was written to bring up the question how injured and rehabilitated koalas can readapt and survive in comparison to those animals that were never injured nor captured.
Most often these kinds of studies only follow the animals until the release in the wild, but this study (read from the article “Post-fire survival and reproduction of rehabilitated and unburnt koalas” written by D. Lunney et al. which can be found on page 576-575 in Biological Conservation 120 from 2004), ends 35months after their release.

Both the uninjured and the rehabilitated koalas were marked and observed 5 days per week from March 1994 until September 1996, then once a week until the end of the project in February 1997.

 

 

Often when the damages to the population are small, the animals can compensate the loss of individuals rapidly, but when the damage to the population is greater like in the major fire near Port Stephens, New South Wales in January 1994 some help to the already threatened species is required. This study is therefore very important in realizing if the human contribution is at help at all. Another great purpose for this study was to see if the rehabilitated koalas displayed a greater naiveté on release due to an extended period of care.
As a comparison group, 23 healthy koalas were captured and released at the same site as the injured ones and was equally followed and observed.

According to the table 1 (D. Lunney et al. / Biological Conservation 120 (2004) 567-575) 9 koalas from both category died. The major cause of mortality was predation of dogs. Also to be considered is that 7 kolas lost their radio contact with the studying group somehow, and those animals are not considered in the study.

Not only the survival is vital for the readapting in the population in the wild habitat, but the animals also have to contribute to the reproduction. Within the study time, there was two breeding opportunities to be considered since the first one was before the fire and the capturing of the animals. The first opportunity was the summer 94-95 and the results were calculated to be 10 and 8 for each of the groups. For the other summer, 95/96, the results were 11 and 8 offspring. 5 out of 9 females bred in comparison to 7 out of the 14 females in the uninjured group.

 

 

Conclusion

The study showed no difference in survival or reproduction between the rehabilitated group and the uninjured group.
With these results we can assume that the human contribution to save the burnt koalas helped the threatened species to regenerate the population, since the injured koalas with high possibility would have died without human care.

An important fact is that both the rehabilitated animals and the uninjured ones were captured and released in the same habitat. This means that they were not translocated which is proven to be less successful in former studies (e.g. Fischer and Lindenmayer, 2000).
The translocation was avoided by regrown Eucalyptus trees  within the months the koalas was in rehabilitation. The average time of care was 168days, and the range was 52-423.

 

 

References

 

D. Linney et al. – Biological Conservation 120 (2004) 567-575