How Increased Light Induces Spring Bird Behavior

February is passing quickly, and so far there is little sign of first Spring, when the earliest birds arrive from their winter homes just a little to our south. However, there is one sign that cold and snow cannot delay or thwart. Early on a cold but sunny February 1, the titmouse sang his courting song, and the woodpecker drummed his fast roll.

It was the sun that did it, swinging the earth around on a string of gravity. It swung our yo-yo planet around until its north-south axis pointed perpendicular to the sun's rays, rather than tilting our northern half of the earth away from those rays.

For those with more poetry than science in their souls, we can say that dawn brightens the sky earlier and sun delays its setting more each day. The increased sunlight falls on plant and animal alike, and even if the warmth is felt only on the face, that is enough.

That light falls and finds receptors in the brains of birds, and that brain in turn emits the hormones that swell the testes of the male and revive the sleeping ovaries of the female. This must begin long before the breeding season begins, because those reproductive organs are shrunken and dormant the rest of the year.

A few sunny days in a row and the birds are all beginning to feel the first urges. The cardinal belts out a round or two of loud whistles, the white-breasted nuthatch mutters his droning yank, and the mourning dove coos his sorrowful sounding whooos. These notes sound like a tiny mellow pipe organ, or as many an inexperienced listener has supposed, the distant hoots of an owl.

It won't be too long before the organs of the dove are swollen to a hundred times their former size, for this species nests early and often. A pair is in such a hurry to get started that they throw together a few sticks on a pine bough and call it a nest. The eggs are laid and half of them fall through to the ground.

In the first few days of February, these songs sound in every yard. They come from those species which are here all winter, unmoving in migration, but still moved by the strengthening sunlight. Not too far to our south the same result ensues in the migrating birds that need bare ground to survive. Restlessness is added as well, so although snow still awaits them here, they are coming anyway, and soon.

Some of our birds are both stay-at-homes and movers. The black-capped chickadee when young is prone to wander. If seeds or larval insects are in short supply in their natal home, they irrupt far south, sometimes in large numbers. During some Novembers at banding stations along the coast hundreds of chickadees are netted and banded in a single night. Despite their efforts many first-year birds are believed to perish, no matter how far they fly in search of food.

If they do last until spring, then they return and join up with the couch chickadees, who have all they want in one place with no reason to migrate. These black-caps form a small flock that "owns" a stand of woods, gleaning food from this larder in never ending swings and circles. Usually a feeding station is shared by several groups of chickadees, especially if it is located in or near an extensive patch of woods or forest.

Each group has a complex social structure with a clear order of dominance by older birds. When February comes the dominant males begin to whistle a gentle song, first note higher pitched, last two lower and run together. It sounds like "Hey Sweetie." For such a diminutive fluff of feathers, the chickadee can act the rakish devil.

Within a group the order prevails, the younger birds giving way to the older, even if they are already perched on the feeder. One at a time is the rule, the young birds slipping in quickly while the old ones sit on the branch and pound, stripping the seed of its inedible husk. Some day that chickadee stripling that left its home and returned, may become the father or mother that rules a resident flock.

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