Why birds spend so much time preening

Green herons don't do Facebook, and they certainly don't use Twitter. They don't play bridge or read novels. Not that they don't have time to fill.

We've often had green herons visit the swampy pond behind our house. This summer, one day in July, we had three at once, a highlight day.

We can't tell boy from girl. We do know that one of the birds was hatched in early summer. Its crest was made of pin feathers.

The herons visit to hunt for swampy pond residents, frogs and mud minnows (a fish new to me; it can breathe air if all it has is mud). The birds are successful as often as need be.

While patiently waiting for a food clue, the birds will preen. They are devoted preeners.

"Feathers are essential to the health and survival of birds," according to the Cornell Lab of Ornithology "Handbook of Bird Biology," so birds devote time to care for them.

Feathers are dead structures; there is no maintenance from within. Birds provide all necessary care from the outside. Feathers need care because they are more than decor. Feathers are complex.

There's more: "Feathers include the smaller down feathers and the larger contour and flight feathers. Larger feathers consist of a shaft (the rachis) bearing branches (barbs) which bear smaller branches (barbules).

"These smaller branches have tiny hook-bearing processes (barbicels) which interlock with the barbules of an adjacent barb to link the barbs into a continuous vane. Down feathers lack barbules, resulting in fluffy feathers which provide insulation below the contour feathers."

When a bird grasps a feather with its bill and slides to the feather end, the bird is, simply put, zipping itself up.

The bird, often after a vigorous shake, pulls itself together, and is a smooth beauty once again.

Birds also preen to distribute oil to their feathers from what is called the preen gland, located at the base of the tail. Preening can also include what we might call sweeping and dusting, and pest control, picking out lice and mites.

Feathers do not cover the body of most bird species as grass covers a lawn. Rather, feathers grow like a neat vegetable garden. Feathers are in rows, called tracts. One row of feathers overlaps another, giving the bird complete body coverage.

For a guy, we'd call it a comb-over.

Research has shown that birds groom less often in winter. Short days make finding food a priority, leaving little personal time.

Feather fact: Black-capped chickadees weigh four-tenths of an ounce. Their feathers weigh four-hundredths of an ounce. But the feathers, true for many bird species, weigh more than the bird's bones.

Lifelong birder Jim Williams can be reached at woodduck38@gmail.com. Join his conversation about birds at startribune.com/wingnut.