Male house finches with elaborate songs have higher reproductive performance

The elaborate songs of male animals are thought to function in either territory defense (male-male communication) or mate attraction (male-female communication). In non-territorial animals, male vocalizations are expected to function primarily in mate attraction, yet the reproductive consequences of male vocalizations in non-territorial animals are poorly described. Here we explore the relationship between male song and male reproductive performance in a free-living population of house finches, Carpodacus mexicanus, a non-migratory, non-territorial songbird. Based on recordings of 20 males, we analyzed three song features (song length, number of unique syllables per song, and song rate) and compared male song with two measures of within-pair reproductive performance (nest initiation date and clutch size) and one measure of extra-pair reproductive performance (whether males sired extra-pair young). We demonstrate a positive association between male song and within-pair reproductive performance; males that sang long songs initiated their first clutch significantly earlier and males that sang songs at a faster rate had larger clutches. Despite the fact that only one of our recorded males sired extra-pair young in the nest of another male, this male's songs were the most elaborate for two of three song features measured, anecdotally suggesting that male song may play a role in both within-pair and extra-pair partner choice. These results suggest that male song is a sexually selected trait in non-territorial house finches.