Dawn chorus start time variation in a temperate bird community: relationships with seasonality, weather, and ambient light

The avian dawn chorus is a daily period of high song output performed predominantly during the breeding season. Dawn chorus performance varies at both the individual and species level. The many extrinsic factors that may relate to dawn chorus start times for different North American bird species have received little attention. In this study, we consider relationships between dawn chorus start times and ambient temperature, precipitation, cloud cover, lunar phase, and Julian date for six common bird species living in a northern temperate rural area. Overall, birds began singing earlier with full or third quarter moon (when moonlight is present at dawn) and with increasing temperature at nautical twilight, and birds began singing later with the presence of cloud cover and precipitation. Our results indicate that a different suite of environmental factors influenced the chorus start times of different species and to different degrees. Alder flycatchers begin singing earliest in this group of birds, followed by Song Sparrows, White-throated Sparrows, American Robins, Eastern Phoebes, and Black-capped Chickadees. This investigation reveals that extrinsic abiotic factors have a significant effect on the dawn chorus start times of north temperate birds, and represents the first comprehensive study of dawn chorus start time variation in North American birds.