One idea is that in the early morning, light levels are too dim for birds to do much foraging but it’s a great opportunity to sing. Another idea is that early morning singing signals to other birds about the strength and vitality of the singer. Singing loud and proud first thing in the morning tells everyone within hearing distance that you were strong and healthy enough to survive the night. This is attractive to potential mates, and lets your competitors know you’re still around and in charge of your territory. Also dawn songs are clearer and more consistent, which allows individual males’ signature songs to be identified easily by their bird neighbors.
Later in the spring, when males sing while the female songbirds lay their eggs in early morning it may reinforce the bond with the female, and dissuade other males from jumping into the nest.
And if you think the birds seem to be singing even earlier in the morning than last year, you could be correct. Research by biologist Mark W. Miller found that in 1929 the first robin songs began about 45 minutes before sunrise, but 84 years later with our neighborhoods flooded in artificial light, robins tended to break their silence more than an hour earlier.
- Brown, T. J. and Handford, P. (2003). Why birds sing at dawn: the role of consistent song transmission. Ibis 145: 120-129. doi: 10.1046/j.1474-919X.2003.00130.x.
- Hutchinson, J. M. C. (2002). Two explanations of the dawn chorus compared: how monotonically changing light levels favour a short break from singing. Animal Behaviour 64: 527-539. doi: 10.1006/anbe.2002.3091.
- Outdoors: Predawn bird songs fading soon by Mark Blazis http://ning.it/LT6Xvk
- American robin song by Patterson Clark http://goo.gl/ERk2f