A hint of dawn is nature's way of telling us to roll over and go back to sleep. Not so for cardinals.

Two cold winter mornings in a row, due to poorly scheduled appointments, I was out of bed just as the first dimness of day created contrast on our snowy yard.

I looked to our row of four hanging bird feeders, expecting to see rabbit shapes nibbling bird leftovers. The snow was alive with birds.

I counted 22 cardinals the first morning and 28 the next. (This has not happened again since that distant day.)

Twenty-eight cardinals is more than an equal share. Our high daytime counts were six or eight then, currently five to seven.

Our suburban lot includes a portion of 10 acres of swamp mixed with brushy thicket and small trees. Our so-called landscaping includes brush piles and uncut weeds. We feed birds generously. Cardinals should love us.

This species has expanded far beyond the former northern edge of its range. The work of man favors cardinals. We have lessened the bite of winter, cleared the forest to create more brushy edges, and we feed birds.

Research shows that cardinals eat at the end of the day to provide the energy needed to stay alive through a cold night. Food at first light replenishes spent energy.

The complexity of survival is found within a formula known as Root's Rule. In short, birds do not winter beyond the point where they can find enough food to maintain their metabolism. That makes sense.

Other species surely do this, too, although not as obviously as red cardinals on white snow at dawn.

Research on wintering chickadees has shown dominance at feeders. If cardinals are similar, adult males eat first, followed by yearling males, then adult females and yearling females.

Dominance was not a survival factor for chickadees.

Cardinals don't migrate. Nine of 10 cardinals banded at their nest site and captured later will be within 10 miles of that nest. The birds form loose flocks in winter, roaming mostly within that range.

The spring nesting territory defended by the male bird will extend from half an acre to five.

If we use two acres as an average territory size and assume that the 28 birds in our yard that morning were half males, half females, all destined to pair this spring (unlikely), their nesting territories would cover 24 noncontiguous acres (the suitable habitat factor).

Apparently, neighbors get to share our winter cardinal bounty.

Male cardinals will choose spring nesting territory during the winter. Their courtship singing is a better sign of spring than the sight of a robin. (Robins' embrace of mild winters has made the sight of one ordinary.)

Studies show that brighter male cardinals hold territories with denser vegetation (safer) and feed their young more often. If you are a female cardinal, those are strong reasons for seeking the brightest boy.

Dominance at feeders can be reduced with multiple feeders, or by scattering seed (black oil sunflower) on the ground beneath feeders. Cardinals readily eat from the ground.

Available food can increase survival because a bird could spend less time searching for food, more time watching for predators.

Watch your feeder birds as they eat. Their vigilance is constant. Foraging in the wild has to be more energy-expensive, with no less time spent being alert for predators, just less productive time devoted to food.

Read Jim Williams' birding blog at startribune.com/wingnut.