For early risers this spring, there is a treat waiting for you in the dark hours before dawn. The constellation Scorpio is shining bright in the southern skies. Antares, the giant star, glows red in the tail of the scorpion. More than that, it is currently joined by two planets, Mars and Saturn.
If you manage to roll out of bed and secure a cup of coffee, you will find this show has a musical accompaniment. Well before the dawn chorus of black-headed grosbeaks, tanagers, house finches, house wrens and collared doves tunes up, the robin lends its voice to the fading darkness. But even before robins begin their song, there is another. While Scorpio still shines, the daily concert begins with the song of the violet-green swallow more than an hour before sunrise.
The song is not the most beautiful, but it is sweet in a modest way. The short jumble of notes is repeated endlessly until drowned out by the larger chorus that comes with brightening skies.
Just try to find the singer. The sound seems to come from every direction. And it does. In near total darkness, the male violet-green swallow launches itself into the night sky and sings while it flies, and flies, and flies.
Tree swallows also begin their solos when the stars still shine. One account has a male beginning its aerial concert before 3 a.m., if one can consider this hour to be morning.
Violet-green and tree swallows are two of several species of swallows that breed in the Rogue Valley. They are common among the oaks, over the agricultural fields, and along the streams. The green back and violet-colored rump give the violet-green swallow its name. The closely related tree swallow is similar, but its back is a uniform steely blue. It also lacks the white around the eye and on the rump. Both species readily accept nest boxes placed high in open areas.
Why sing in flight? Why in the dark of night?
These swallows aren’t the only birds to sing while flying. Many grassland birds sing while in flight, but their efforts are much briefer. East of the Cascades, horned larks rise high above the grasses to sing a series of songs for a minute or so before dropping back to earth. By rising above the vegetation, they can be heard clearly by neighbors, staking claim to a piece of grassland. Pipits and skylarks in Europe do the same.
But why violet-green and tree swallows? They roost in trees and on power lines, plenty high enough to be heard over great distances. And swallows don’t defend territories any larger than the immediate space right around the nest. Moreover, they continue this display of endurance well into incubation. So mate attraction isn’t the answer either.
And then there is the cost. Flying is energetically expensive, about 15 times the cost of perching. In the animal world there is seldom such an abundance of food to tolerate this kind of performance, especially when it seems to serve little purpose.
While I enjoy the time around dawn, I admit this is not my finest hour. The coffee has yet to kick in. So I leave the solution to this small puzzle to sharper minds.
Stewart Janes is a biology professor at Southern Oregon University. He can be reached at firstname.lastname@example.org.