vocalizations can play a wide variety of different roles. in groups such as anurans and birds, several distinct types of notes are incorporated to form songs, which are sung in different situations and serve distinct functions. for example, many frogs may use trilling notes in mate attraction, but switch to different vocal patterns in aggressive territorial displays. in some species, a single song incorporates several note types which serve different purposes, with one type of note eliciting responses from females, and another note of the same song responsible for warning competitor males of aggression.