Associations between bird song attributes and noise, light, date, and temperature: vermilion flycatchers (Pyrocephalus rubinus) sing shorter and higher pitched songs in territories with more artificial light at night

Urban noise and artificial light at night (ALAN) are global pollutants affecting animal acoustic communication. A previous study that measured noise, but not ALAN, found that vermilion flycatchers produce longer songs in noisier territories. A subsequent study in another population, that measured noise and ALAN, found that males emit longer songs in brighter, but not noisier, territories. The negative result could be due a lack of sufficient noise variation in the latter study. We evaluated the contribution of noise and ALAN on song length, provided sufficient variation in noise and ALAN. We also measured song peak frequency. During the dawn chorus, we recorded songs of 41 vermilion flycatchers in two populations (UNAM and PERM), and measured noise, ALAN, and temperature. For the population with sufficient noise and ALAN variation (UNAM), we confirmed that song length was positively associated with noise; it was also negatively associated with ALAN, especially in those males recorded late in the breeding season. At UNAM, we found an overall positive association between song pitch and ALAN; additionally, males singing at relatively low ambient temperatures (12-15 °C) produced higher pitched songs as ALAN increased. Those singing closer to new moon and at relatively low ambient noise levels (43-54 dB[A]) sang higher pitched songs in brighter territories; these two results should be taken cautiously. Our results show that light, noise, date, and temperature are associated in unexpected ways with song length and pitch, potentially affecting song information content and sexual selection.