''In Canberra,'' writes David Graham, of thereabouts, ''sulphur-crested cockatoos have learnt to bungy jump. They pull the rubber seal out from street lights, stand on top of the light with the rubber in their claws and jump off. They end up hanging upside down with their wings spread out, squawking. They then fly up and do it again, and again. They look like they're having a great time.''