How can you tell the difference between a male and female koala?

Male koalas are generally larger than females and their testicles are sometimes visible. They have a longer, broader face and as adults are more muscular. At sexual maturity (2 -3 years) they develop a scent gland on their chest which looks like a dirty, vertical mark down the middle of their upper chest. They use this scent glad to claim their territory by rubbing it against the trunks of their trees.
Females are generally smaller, with fluffier ears. They have a rounder, softer face and are smaller in size.
Having said that, some females have broad faces and some males have lovely fluffy ears. There are always exceptions to the rule with koalas!