In the northern white-cheeked gibbon, males and females look strikingly different: males are all black with white whiskers on their cheeks, while females have a creamy beige coat. It is one of the few mammals whose colour changes so dramatically with age: the young are born blond and turn black at around two years old, then the females turn blond again when they reach sexual maturity. Every morning, couples sing powerful duets to mark their territory. It is Critically Endangered in Vietnam and China, but there is new hope: a new colony was recently discovered, found thanks to its song.