Song structure of male Northern House Wrens and patterns of song production and delivery across the nesting cycle

Studies of the role of bird song in avian communication have revealed numerous functions across many species, including its critical importance in female mate choice (intersexual selection) and male-male competition (intrasexual selection). A first step in understanding the role of song in different contexts is to describe the note, syllable, and song-types that occur, as well as their patterns of production within a population. Here, we do so for a north-central Illinois, USA, population of Northern House Wrens ( Troglodytes aedon ). As has been described in other populations, most songs (≈ 1–3 s in duration) contain an introductory section of soft, broadband notes followed by a terminal section of loud, frequency-modulated syllables that tend to be trilled. In characterizing the contents of 3.919 songs produced by 32 males throughout the breeding season, we identified 62 distinct notes, from which 76 syllables were produced. These syllables were organized in patterns largely unique to the individual—most notes and syllables were shared across the population, but almost no song-types were produced by more than one male. Singing declined over the course of the nesting cycle, and throughout the breeding season. Song production was at its minimum while fertile females were egg-laying, suggesting that males may change singing behaviour to guard against extra-pair copulations, which tend to occur at this time.