Cassowaries are large flightless birds, only slightly smaller than an ostrich or emu, that live in the forests of New Guinea and north-east Australia. Their most distinctive characteristic is the large crest, or crown, on the top of their head. The outside is hard like a horn, but the inner part has a honeycomb-like structure to keep the weight down.
There are lots of theories for the purpose of the crown. It may have originally evolved to protect the bird’s head. Cassowaries eat fallen fruit and the wedge-shaped crest would help deflect any fruit/seeds tumbling from the treetops. Cassowaries can also run at 48 kilometres (30 miles) per hour, and as they career through the forest they lower their heads to push through the undergrowth. But the honeycomb interior does more than just save weight – it also acts as an amplifier. Cassowaries have the deepest call of any bird. The note is so low it is only just audible to humans, but the crown acts as a resonating chamber that allows this sound to carry through the dense forest. Besides these useful qualities, the cassowary’s crown may play a decorative role as well. Like the peacock’s tail, size matters when it comes to attracting a mate.