The koala

The koala's whole existence is organised around one intractable food. Eucalypt leaves are low in energy, loaded with oils and toxins, and armoured with indigestible fibre — the sclerophyll leaf economy (see sclerophylly), the same tough, defended, phosphorus-hoarding leaf that scarce soils force on the gums in the first place. Almost no other mammal will eat them. The koala gets away with it by spending as little as it can: sleeping some twenty hours a day, moving slowly, and running a low, frugal metabolism and a gut full of microbes that ferment the leaves and disarm their poisons. It is a beautifully disciplined way of life, and for as long as the trees hold still it works, because nothing else is competing for the food.

The bill comes with the fit. That dependence ties the koala not to eucalypts in general but, in practice, to a particular set of preferred feed-tree species, growing densely enough and close enough together that an animal can move between them without coming to ground. So a koala population needs three things of a forest at once: the right feed trees, enough of them, and connection — trees joined closely enough to cross safely. It also leans on the big, old trees the forest is slowest to grow, for shade, shelter and safe passage through the canopy. Take any of those away and the bargain unravels, and the modern landscape has taken all three: across South-East Queensland, including this coast, koala forest has been cleared for farms and suburbs, carved into fragments by roads, and isolated into patches too small or too far apart to hold a population. The result is one of the most-studied wildlife declines in the country. Long-term work across the region has tracked the toll of vehicle strikes, dog attacks and habitat loss (Gonzalez-Astudillo et al. 2017; Dissanayake et al. 2019), and, running through it, a chlamydial infection (Chlamydia pecorum) that causes blindness, infertility and death (Robbins et al. 2018). In a couple of human generations the koala has gone from common to officially threatened, listed Endangered under the EPBC Act for the combined Queensland/NSW/ACT population on 12 February 2022 (uplisted from Vulnerable). It is not the first time we have pressed it hard: in the 1927 "Black August" open season alone, Queensland's fur trade sold hundreds of thousands of koala skins (Hrdina & Gordon 2004).

The vaccine, kept honest. One of the more hopeful pieces of science on the coast is, of all things, a koala vaccine, developed over more than a decade at the University of the Sunshine Coast (Timms and colleagues) against the chlamydial disease. A wild-population trial reported a 64% reduction in chlamydial mortality in vaccinated animals (Phillips et al. 2024), and in June 2025 the national regulator granted a minor-use permit (APVMA PER94984, valid to 2027) — a permit for wider use, not full registration. It is a real feat, and a homegrown one. But a vaccine treats one threat in the koala's path and cannot manufacture forest: you cannot inoculate an animal against bulldozers and traffic. Read against what it needs, the koala's deepest problem stays brutally simple — enough connected trees to live in.

This is also why the koala can stand for far more than itself. It shares the gum forest with a whole cast staked on that forest's slowest-built resources — the gliders, owls, parrots and the glossy black-cockatoo that cannot breed without a century-old hollow (see hollow-dependence). The koala does not use hollows; its own dependence is the feed trees and the connection between them. But to keep the forest standing and joined up for the koala is, in the same stroke, to keep it for the hollow-nesters behind it — which is why saving the emblem, properly done, saves the parade.