March. April 61populations, to deal with specific eucalypt toxins, could help
explain that. This also may explain why it’s proved to be so im-
portant for researchers and carers to return a koala to the same
area, and preferably the same tree, from which it came.
B
EYOND NATURAL DISASTERS, koalas face a long list of
other threats. The negative impact of habitat clearing is
ubiquitous across the country as it is for so many other
species. But the other major threats differ in different areas.
Domestic dog attacks and impacts with cars are huge problems
for koalas living near urban or developed areas, as many northern
NSW and southern Queensland populations do.
The sexually transmitted bacterial disease chlamydia, how-
ever, is the biggest problem for many koala populations right
across the species’ range. In northern NSW, for example, it’s
considered the biggest day-to-day threat to the species. There are
many strains of chlamydia in many different mammals through-
out the world. It’s likely the koala is affected by its own strain
but has evolved to deal with it over millennia. But the form of
chlamydia causing widespread infertility and death in koalas
right across their range now is almost identical to what’s seen in
livestock. And it’s thought the original form entered the koala
population when pigs, cattle and sheep were brought to Australia
by European settlers during the early 1800s. How the bacteria
crossed over into the koala population, bearing in mind it’s a
sexually transmitted disease that affects mucous membranes, is
unclear. No-one really knows, but ticks may have functioned as
a kind of intermediary vector. However it arrived, koalas don’t
seem to have much natural ability to deal with it.
Chlamydia is often rampant in drought-stressed populations.
“Drought reduces the available moisture in eucalypts for koalas
who rely on this for their daily intake, so koalas become constantly
dehydrated,” Cheyne says. “Eucalypts have measures to protect
their foliage in these conditions, so their leaves become more toxic
and unpalatable. The koalas struggle to find available food and end
up emaciated as well. All of this puts pressure on their immune
system, so diseases such as chlamydia become expressed more.
The result is very sick koalas that often end up in renal failure.”
All animals brought to the hospital are examined using
ultrasound and it’s rare that an animal doesn’t show signs of
infection. Every animal that dies at the hospital, or is brought
in dead, is also subjected to a post-mortem. This often reveals
advanced chlamydia infection has played a role in the animal’s
demise. Antibiotics can kill or control the disease but koalasSydney University researchers tag and
microchip Liverpool Plains koalas they have been
recruiting to a long-term study of the effects of
climate change on the species. Captured animals
usually take a few moments to orient themselves
after release back to the wild, before scampering
up a tree.Researchers can estimate a koala’s age by the
level of wear on its teeth. This one (top) is less than
seven years old. Long sharp claws and front paws
that each have two opposable thumbs, allow koalas
to move around trees with great dexterity.