Conspecific challenges provoke female canyon wrens to sing but not to duet

Abstract

Abstract: Song by female birds is rare in some species, particularly at north-temperate latitudes. Nevertheless, female song can carry important signal content and may be used in functional ways, both when sung solo and when combined into partner duets. Evidence supports the idea that duets reflect elevated threat levels because they indicate partner cooperation, but this comes from species with frequent female song and duetting. Here we asked the following questions about infrequently given female song in canyon wrens (Catherpes mexicanus) in Western North America. Do female birds use song in a context that implies functional significance? Do canyon wren mates combine their songs to form duets? Are duets a more threatening signal than non-overlapping dual-sex solo songs? To address these questions, we challenged canyon wrens with paired simulated intruders singing alternating solo songs or duets formed by overlapping male and female songs with consistent timing. Results indicated that female canyon wrens approached and sang in response to conspecific song playback as quickly as males did and increased their song rates significantly. Partners did not overlap their songs to create duets more often than expected by chance, and neither sex responded more strongly to duets than to solo songs. Outcomes match the prediction that duets only carry different signal content from solo song in species that frequently duet, and suggest that canyon wren female song is highly functional despite being rarely used outside of contest situations. Significance statement: Animal signals mediate social interactions in myriad ways. The majority of studies of avian song have focused on conspicuous, frequently given, signals but infrequently given signals may also have important fitness consequences. We examined how the usage of a rare signal, canyon wren female song, changed during contest situations and in response to a coordinated duet versus non-coordinated solo songs. Rates of female song increased significantly during contest situations, but duets did not provoke stronger responses than solos. Although duets are threatening to species that duet (including many wren species), they do not appear to be universally salient. Canyon wren female song, in contrast, carries strong signal content despite being used infrequently outside of contest situations. Results highlight the potential functionality of rare signals, as well as the variability in signaling strategies across avian species.