Cassowary
Biologist Andrew Mack has watched cassowaries and disagreed with many of these ideas. He thinks that the casques play a part in the way cassowaries hear sounds or the way that they make sounds. He discovered that the dwarf Cassowary and southern cassowary make a very low sound. It is the lowest known bird call, like a "boom", which people can only just hear. The southern cassowary sound was measured at 32 hertz, and the dwarf cassowary was even lower at only 23 hertz. The birds live by themselves, they do not live in groups so the "booming sound" might be a way for the birds to communicate (talk) over a long distance in thick rainforest. Some scientists think that this may be how dinosaurs communicated with each other.