Koala
Ecology and behaviour
A female koala has two teats; the joey attaches itself to one of them and suckles for the rest of its pouch life. The koala has one of the lowest milk energy production rates in relation to body size of any mammal. The female makes up for this by lactating for as long as 12 months. At seven weeks of age, the joey's head grows longer and becomes proportionally large, pigmentation begins to develop, and its sex can be determined (the scrotum appears in males and the pouch begins to develop in females). At 13 weeks, the joey weighs around 50 g (1.8 oz) and its head has doubled in size. The eyes begin to open and fine fur grows on the forehead, nape, shoulders, and arms. At 26 weeks, the fully furred animal resembles an adult, and begins to poke its head out of the pouch.
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