Context-dependent variation of house finch song syntax

We explored the role of social context in the syntactical variation of house finch, Haemorhous mexicanus, songs using both traditional song measures and network analysis. In comparison to solo bouts, the bouts of countersinging males had increased syntax diversity, with higher numbers of simple paths and transition types (but not syllable types) in comparison to solo song, which had high sequence consistency. Both the proportion of introductory syllables and the degree (number of transitions to and from those syllables) increased in countersinging bouts and were an important source of syntactic variability. In contrast, courtship bouts included longer songs and longer syllables than both solo and countersinging bouts, but were similar to solo songs in sequence consistency. The longest courtship songs often included concatenated sequences that formed ‘compound songs’, or repeating strings of main song syllables, which slightly increased the degree of those syllables. Our results suggest that interactions between males are associated with increased syntactic variability in song delivery while female choice favours signals that maintain species-typical syntax and demonstrate fitness in terms of a male's capacity to sing extended songs.