 Adult and young New Guinea crocodiles have a range of vocalisations . An adult female can produce a repeated throaty " roar " when approached by another adult . The young start communicating with each other while still in the egg ; this may help synchronise hatching . Newly hatched juveniles use various yelps and grunts . When startled , a warning sound emitted by one will send all the juveniles diving to the bottom of the water . Adults in the vicinity respond with growls , threats , and attacks . The distress noises of a youngster when handled at a ranching facility was observed to cause all the larger animals to become involved in frenzied activity , with some rushing towards the juvenile and others thrashing about in the water and slapping their heads down on the surface . 
