Take another look at the forlorn robin sitting in the fence of a Chicago suburb in midwinter. He is not what he appears to be. You might think he is the first robin of spring who, eager to get started on his work of gladdening humanity, took off too soon and got caught in a late-season storm. More likely, this is not the case at all—the robin has probably been around all winter and is waiting to migrate further north. It's another one of those things about which romanticists and scientists have divergent views and which even scientists admit they still don't fully understand.
Migration means a great shift in the robin population. Some of them nest farther north than others and some go farther south. Just what makes them go where they do and when they do has never been fully explained. There is a whole set of environmental and physiological factors that combine to make the robins move north in the spring. The increasing length of the day is believed to be a dominant factor.
Whatever starts them off, the birds are ready for the long trip. Big deposits of fat give them the energy necessary for sustained nights. They are moved by a force which they cannot resist. It brings them back to the same place where they nested the year before. The males go first, for it is their job to decide where the summer home will be located.
When a male robin arrives in an orchard or yard he lays claim to a territory with fairly definite boundaries. It is in this territory that the nest will be built. Then he proceeds to warn off other robins. To us it may be a song, but to the robin it is a proclamation of squatter's rights.
But there are other males about who dispute his claim. Those frantic fights you see on the lawn in spring are cock robins settling problems of real estate. And the robins that beat themselves against a window or the windshield of an automobile are not always off their rockers. They frequently mistake their reflections for a territorial rival and try to drive him away. Remove the reflection and the bird stops this foolishness.
HOW ROBINS FIGHT
These fights between male robins are not lethal and I don't have any record of knockouts at hand. The robin is a light puncher but his footwork is good. Dr. Howard Young, who has refereed many a robin match at the University of Wisconsin, points out that the cocks square off in four stances for ground attack: the tail lift, the crouch, the attack run and the normal. In the tail lift the head is lowered and the tail is elevated at an angle of about 45°. In the crouch the robin squats in threatening readiness. In the attack run the bird moves in low with knees bent. In the normal the bird stands upright and slugs without feinting.
When the females begin to arrive a week or two later the home territories are pretty well established. The singing is not primarily to attract a female. It does let the presence of a male be known but it doesn't inform the female whether he already has a mate. The females blunder into the territories and are accepted by the males. Barring accidents, the pair remains together for the summer, normally rearing two batches of young.
The robin's territory includes an area for collecting food. The robin tugging an earthworm out of the lawn is a traditional American sight. Sometimes he stands poised and motionless in a listening attitude before he makes a stab at the end of the worm. It may be that he is listening to the underground movements of the worm, although I don't know that this has been proved. It has been demonstrated, however, that blindfolded owls can catch mice.
When fall comes, the miracle of migration happens again. The friendly robins on the lawn undergo changes. They no longer putter about the yard showing little fear of man. Instead they become wary. They gather in flocks and their whole attitude changes. Traveling at night in great squadrons, they join in the general movement of millions. At Cape May, N.J., as many as 10,000 robins have been seen passing a given point during the early hours of a single morning. They are wild things moved again by something beyond their control.
Our bird here in the snow is the central figure in a great mystery story. As one scientist says, "We just don't know enough about enough species of birds."