It was just before sunrise when I heard a familiar sound almost forgotten. It was the clear song of a northern cardinal. I stopped in my tracks and listened with utter appreciation. As I stood there, I realized the significance of the moment; though it was very cold and flurries dusted the yard, this bird was getting ready for nesting.

It may sound unbelievable, but if you wake early and head out into the stillness of a winter morning you, too, will hear a few birds calling. Where I live, the cardinal is usually the first to start singing. Consequently, I listen carefully to them each winter, knowing that what begins with a few notes later increases to full song by March.

While most of us notice birds becoming vocal in the spring, many ornithologists say birds begin singing almost immediately after the winter solstice. It hasn't been widely accepted, and the research is fledgling, but there are a few renowned ornithologists who have charted the immediate explosion of bird call and song as early as Dec. 23.

It all makes perfect since. Birds are extremely sensitive to the light. Changes in light intensity determine major aspects of behavior and life cycle. Light affects hormones, and biochemical changes that incite courtship, mating and song. But are they likely to respond so dramatically to such an infinitesimal increase in light? I believe they are, and swear that just a few days after the solstice there was an increase in vocalization.

In the weeks to follow, the cardinals around my home will keep me inspired and very much in tune with the advancing daylight as they sing more often. On the surface, it seems the cardinal’s song is nothing so special, but closer scrutiny reveals the complex way in which the bird utilizes its song. After years of careful listening, I have noticed some of the key elements in cardinal communication.

The secrets lie within the way male cardinals answer rivals — whether or not males match each other’s song or abruptly switch to a new song or sing more rapidly. Interestingly, females also sing, and the communication between pairs is extensive. There is meaning behind such slight changes in their exchange, such as whether they answer one another, or whether they overlap replies, or alternate, or if the male matches her song, or she his. The frequency, pitch, context, and number of phrases all convey specific information, too.

The cardinal’s song is unmistakable, and birders anywhere in Connecticut can easily recognize its pure whistle (allaboutbirds.org). Listen for its classic "What cheer cheer birdie birdie birdie" or "Cheer cheer whit whit whit," and you, too, will have the key to understanding the complex code of cardinal language as the mating season progresses.

I know of only a few things that they are expressing, but knowing complex communication is taking place instills a sense of wonder. Now when I watch the cardinals feasting on the striped sunflower, black oil sunflower, and safflower seeds they relish, I appreciate them more. As I continue to listen, and study up on bird song, the world of the cardinal will surely reveal itself.

In the meantime, when that early spring wind wrestles with the trees and the bitter cold stings my face and hands, the thought of a spring harbinger having already begun on the first day of winter will be encouraging. Soon, the sun will shine brighter, and the music of other birds will join with the cardinal, loud, persistent and unquestioned.

Robert Tougias is a Colchester birding author. His book "Birder on Berry Lane" is now available. You can ask him questions at roberts90gtias@yahoo.com.