A new study reveals that the calls contain frequency changes that dolphins recognize . humans are one of the few animals that use sound modulation instead of simple voice differences to identify individuals 举例来说，如果是海豚妈妈在呼喊小海豚，那么人们认为这只小海豚能够从妈妈的喊叫声中识别出自己的“名字” 。
