This is BirdNode, a Robin tugging at earthworm from the ground in spring and summer is the

quintessential image of a backyard bird.

But as fall gives way to winter, many earthworms in cooler parts of the country retreat deeper

into the soil and warmer realms beyond the Robin's reach.

At this time of year, these normally solitary birds flock together in an adaptive strategy

that makes it easier to find fruits and berries on widely scattered trees and shrubs.

With spring, the ground begins to warm, though.

The Robin start to notice slight movements in the soil from the worms' burrows, and once

again seek out these nutritious invertebrates.

Everyday earthworms are higher in protein content than either beef or chicken.

You'd have to eat around a pound of soybeans to equal the protein in just three ounces of

earthworms, and they're high in calcium, and easy to catch compared to an agile crickets

or a butterfly.

Put that all together, and you have pretty much a superfood for birds, and youngsters

in particular, hidden deep in the soil throughout the winter until a springtime date with destiny

and the beak of an American Robin.

For Birddoughed, I'm Michael Stein.