Action on Koala numbers

Large concentrations of koalas in the Adelaide Hills are causing damage to some areas of woodland and threatening the animals’ long-term welfare. Natural Resources Adelaide and Mt Lofty Ranges has responded by starting a fertility control program to reduce breeding over time and preserve the koalas’ habitat.

The most recent population survey produced estimates of approximately 150,000 koalas in the Mt Lofty Ranges, with very high densities in some areas of koalas’ preferred Manna Gum woodland.

“In one area of woodland in the central hills, 13 koalas per hectare have been recorded and we are now seeing severe impacts due to over-browsing. Optimal koala densities to prevent over-browsing of their habitat and ensure the long-term welfare of the koalas is around one per hectare,” according to the Natural Resources department. “As a direct result, there’s considerable evidence of over-browsing of preferred food trees, with severe defoliation, dead or dying trees and multiple koalas observed in impacted trees in numerous parts of the Mt Lofty Ranges region. In effect, one of the greatest threats to the koala population in parts of the Mt Lofty Ranges is the koala population itself.”

Hormone implants are being inserted in about 200 female koalas in areas where high over-browsing has been observed. Trained staff capture the koalas and place the implant while the animal remains at the base of the tree. It is then tagged and released after a process that takes about 10 minutes.

Regional Director Brenton Grear said a long-term program using the implants on Kangaroo Island had reduced koala density and improved tree health.

“We have to ensure that the koalas’ favoured eucalypt woodlands are sustained, and the reality is that koala density in some parts of the Mt Lofty Ranges is unsustainably high,” he said.

Koalas are not native to the Adelaide and Mt Lofty Ranges (AMLR) or Kangaroo Island (KI) regions. They were introduced into both regions from Victoria in the early 1900s after hunting for the fur trade severely impacted on the population in that state.

“Although some groups have stated the total Australian koala population is less than 100,000, our on-ground surveys make us confident that the number in the Mt Lofty Ranges alone is around 150,000.