Have you noticed the change in the air? Spring officially has arrived with the Vernal Equinox, and you don’t need a calendar to tell you. The birds in your backyard tell you with their song.

The quiet of a winter day is due partly to the absence of bird song. During the non-breeding portion of the year, birds simply don’t sing, because song is used to defend territories and attract mates. Bird song sounds lovely to us humans, but its purposes are clearly defined to the bird. What you will hear outside of breeding season are calls, which include the short chips and dee-dees and peeks that birds use to keep in contact with each other or to warn of danger. When breeding season begins, bird calls are still heard, but now the song begins.

Spring — that is, breeding season — began in our backyard with male Black-capped Chickadees starting their “fee-bee” song. You may hear this song during the winter on a lovely sunny day; I think I remember first hearing it this year in January, although I considered it a false alarm at the time. But now, with the arrival of true spring days with longer daylight and increasing warmth, the fee-bee song is constant. The small flock of chickadees that spent the winter with us is beginning to change, with the males now rivals for the females and for the territory that includes this backyard. The breeding territory of chickadees averages from 10 to 13 acres, so there probably will be only one or two pairs of breeding chickadees nearby when the final lines have been drawn. The pairs will continue to form within the flock for a few more weeks now, then will separate from it in late April or early May to begin nest building and egg-laying.

Northern Cardinals have begun to sing, too. Several weeks ago we began to hear the clear, whistled cardinal song in the first hours of daylight, starting the marking of territories after a winter spent quietly foraging under our feeders. At first there was one male, marking his territory in the yard around the house. He sits in the tippy-top of one tree, sings for a few minutes (“my tree, my tree, my tree”), then moves to another tree nearby, sings there for a few minutes (“my tree, my tree, my tree”), and continues the process until he has marked the boundary of his entire territory. There can be no doubt where a nesting territory is, and the other cardinals know. (For several years we had two mating pairs whose territory boundary ran between the shade garden and the shed. Several times during mating season we watched the two males fight if one crossed over the line.)

In the last week, there have been two cardinals countersinging out there, first one bird from the house yard, then the second bird, repeating the first one’s notes from a tree way out in back. During the winter we did see two male cardinals occasionally, along with one female. Now, however, because I can’t see who is singing out in back, I don’t know if there are two males announcing separate territories, or if a male/female pair is singing to each other. Other than the fact that it’s early for them to be actively courting, there is no other way to differentiate between the two types of singing. And yes, female cardinals sing, unlike many other bird species where only the male sings. I’ll have to keep watching to see what our situation is.

There will be more and more sounds of spring as we move through the coming weeks. Some of our other winter residents are beginning to sing a bit, such as our goldfinches and house finches. Birds that have arrived from their winter homes but aren’t singing yet will begin to — for example, waves of robins are beginning to be reported in the area, but I haven’t yet seen a report of a singing robin around here (or heard one myself, for that matter). Keep your ears open as well as your eyes. Spring is popping!