Table 2.

Definitions for song characteristics used in this paper

Song trait	Definition
Syllable repertoire	Mean total number of unique syllables an individual uses across songs
Syllables per song	Mean number of unique syllables used per song
Song repertoire	Mean total number of unique songs an individual produces
Intersong interval	Mean length of time separating songs within a period of consistent singing behavior (unit: seconds)
Song duration	Mean length of a song, measured as the length of time of consistent singing or discrete songs between periods of silence; sources may have differed in definition based on the song structure of a studied species (unit: seconds)
Song rate	Number of full song cycles produced per minute, computed from song duration and intersong interval values
Song continuity	Proportion of total song performance time spent producing song, computed from song duration and intersong interval values

Here, we note the definitions that we used throughout our analyses. Some previous studies have characterized birdsong in different terms; for example, what we term a “syllable” is also called a strophe, note, element, etc. Further, Read and Weary³⁰ define “syllable repertoire” as the number of syllables in a single song, whereas we classified those data as “syllables per song” in our database. When we gathered song characteristic data from cited sources, we classified these data according to the definitions given in that source, regardless of the terms used