another major function of song output is to indicate aggression among males during breeding seasons. both anurans and birds use singing in territorial displays to confer aggressive intent. for eastern smooth frogs ("geocrinia victoriana"), for example, courtship songs involve shorter notes to attract potential mates, and are followed by longer tones to repel males. frequency of sounds produced generally negatively correlates with body size both within and among species, and allows competing males to assess body size of vocalizing neighbouring frogs. male frogs typically approach higher frequency sounds more readily than lower frequencies, likely because the frog producing the sound is assessed to be a smaller, less dangerous competitor.