How did koalas become threatened?

They are listed as a species of least concern, not threatened. Population of over 100,000.

There is considerable contention over the status of the koala. The Australian Koala Foundation estimates koala numbers have dropped below 80,000.

Koalas are not officially classed as "threatened" by any authority within Australia. Their status varies from "secure" or "common" in many areas to "vulnerable" in localised regions such as southeast Queensland, and "vulnerable" in New South Wales (after previously being "rare and vulnerable" in 1992).

Due to farming and land clearing, native koalas were eradicated from Western Australia and South Australia in the last century, but moves have been made to reestablish new colonies in both states.

Despite urging by conservation groups since around 1992, Australia's federal government has refused to list the koala as vulnerable, threatened or endangered. Even international conservation groups cannot agree. Meanwhile, the International Union for Conservation of Nature (IUCN) lists the koala as "potentially vulnerable", while the US Endangered Species Act lists the koala as "threatened".

The main threat to the koala is habitat loss. Koalas inhabit prime land which man has decided is better used for housing developments. Not only do the koalas lose their sources of shelter and food, they are subject to dog attacks and being hit by cars as suburbia extends further outwards. A prime example of this is southeast Queensland, where koala numbers have dropped to 60% less than what they were a decade ago, entirely due to increased development - and where they now face extinction by 2020.

Koalas are territorial, and they live in complex social communities where each member has a certain number of trees within its territory. When access to these trees is cut off by new roads, the koalas will still try to cross the road, and risk being hit. Relocation of koalas is rarely successful because their territorial and social habits are largely misunderstood.

Another significant factor is predation by introduced species such as dogs and foxes.

Koalas are also subject to the disease chlamydia, which affects the koalas' fertility, and eventually leads to their death. Currently, there is no cure for this disease. At the best of times, the koala is a slow breeder, usually producing just one joey a year.