The social interaction role of song in song sparrows: implications for signal design

Many territorial songbirds use singing as an interactive social signal to reduce inter-neighbor aggression. Communicationtheory predicts that territorial songbirds may use repertoires of signals to indicate graded levels of aggressive motivation.This theory is supported in song sparrows, a species that uses several different song-based signals such as song-type matchingto escalate or de-escalate aggression during counter-singing interactions.

John M. Burt & Michael D. Beecher, Comparative Cognition & Behavior Reviews, 3 , 86-98, 2008