Morning birdsong starts well before the sun

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Those who arise early or tend toward insomnia are fully aware that many spring birds begin the day painfully early. The impending day may be showing only the barest hint of pale sky on the eastern horizon, but tree and violet-green swallows have already taken flight to serenade the countryside from pitch black skies. Soon American robins join in with a flute-like song delivered at a deliberate pace. Western kingbirds reveal themselves to be excellent songsters in the dark, songs never heard when the sun is in the sky.

At 40 minutes before sunrise — when you must still exercise caution retrieving the morning paper or you might trip over a neglected toy or garden tool — other singers join the chorus in rapid succession until it is nearly impossible to pick out a single performer. When the sun finally breaks the horizon and strikes the treetops, many birds fall silent. The day has begun, and there are other tasks. Singing later in the morning is less intense and more sporadic, though no less welcome.

The pre-dawn chorus of birds presents an interesting puzzle for ornithologists, one that has defied a clear explanation. Why sing in the darkness? Why not wait until one has had a good meal or at least is able to bask in the morning sun?

Singing birds bring joy to those who take time out of the day's rush to listen. People often reasonably assume that birds sing for the joy of it. Maybe they do, but such joy can come with a death penalty, something humans often fail to consider given the relative security in our lives. We do not have to concern ourselves with being eaten by some predator on the way to the store. Most of us don't have to worry about starving to death before breakfast.

A bird who sings is advertising its presence. It's good when attracting a mate or reminding a neighboring bird that this yard is occupied, but others are listening, too. Western screech-owls take a toll on early singers. With just a little more light in the skies, Sharp-shinned and Cooper's hawks focus in on singing birds for breakfast.

Then there is the energetic cost of singing. The last caterpillar or worm eaten came the evening before, and a tiny bird can store little fat. Most or all is used up during a chilly night. It would make sense to get a bit of a meal before greeting the day with song, and yet here they are belting out song on the edge of death by starvation. Recent studies have indicated that singing indeed takes a lot of energy. So why sing before sunrise?

Your guess is as good as mine. Some have suggested that if it's too dark to forage, why not sing. (If those are the options, I say, "why not sleep?") Others suggest it is to announce to the female that the male survived another night and please stay faithful. (Birds fool around quite a bit.) Still others have suggested singing is an invitation to mate. Most matings between birds occur early in the morning.

The ornithologist in me thrives on such questions. Then there is the birder in me that simply enjoys listening to the dawn chorus, coffee in hand with slightly sleepy eyes.

Spring is here.

Stewart Janes is a biology professor at Southern Oregon University. He can be reached at janes@sou.edu.

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