Layers of Wintering Birds

     While watching a few species of birds along the edge of a bottomland woodlot in Lancaster County, Pennsylvania for an hour one afternoon early in December, I thought about how different kinds of birds occupy a specific layer or more of woodland, though there is some overlap among the various bird species.  The few types of birds I saw that afternoon were examples of various species using different levels of a deciduous woods.
     A permanent resident song sparrow and a wintering winter wren were each along a stream at the edge of the woodland I was enjoying.  Though these common species winter in different habitats, there was enough woods there to satisfy the wren and enough weedy edges to please the sparrow.  Therefore, these two adaptable species were wintering in the same place, though it is unusual for these kinds of birds to live in the same environment. 
     However, the song sparrow and winter wren have traits in common.  Both kinds are brown, which camouflages them in their common habitat of mud flats and gravel bars along small, flowing waterways.  Both species feed on invertebrates through winter, though the sparrow also eats seeds.  And the wren holes up for the night among tree roots at the waters' edge, while the sparrow nestles deeply in clumps of tall grasses and weeds.
     I saw a resident male northern cardinal and a little, scattered group of wintering white-throated sparrows low in thickets of red-twigged dogwoods, spicebushes, burning bushes, and tall weeds and grasses in the south-facing, sunny edge of the woods near the waterway.  These small birds were moving around and scratching up weed and grass seeds under the protective shrubbery.  That cover will be handy if a hawk or cat stalks those busily feeding birds.
     That afternoon, too, I saw a northern mockingbird, a few eastern bluebirds and a handful of cedar waxwings feeding on poison ivy berries on a vine halfway up a large tree.  Devout berry eaters in winter, those little birds were attractive in the sunlight as they consumed those dirty-white berries.  Probably full of berries, the mocker dove into a nearby shrub and stayed there to rest and digest in relative safety.  And, within several minutes, the bluebirds and waxwings simply drifted away to safe places to rest and digest the berries they ingested.
     A lone Carolina chickadee fluttered among buds, twigs and small limbs in the sapling layer of the woods as it looked for tiny invertebrates and their eggs in crevices.  Chickadees, titmice and other kinds of small, woodland birds can be spotted in a few levels of a woods, but usually not in treetops in winter because they are vulnerable to cold wind.
     I also noticed a northern flicker, which is a kind of woodpecker, and a red-bellied woodpecker in the treetops where they usually are.  Both these handsome species were chipping with their sturdy beaks at loose bark and dead wood on limbs to dig out invertebrates living in those branches.
     And I saw a turkey vulture and a pair of red-tailed hawks sailing over the treetops of that woodlot.  The vulture was looking for carrion to eat while the red-tails were watching for gray squirrels to catch and ingest.  These two kinds of soaring birds usually perch in the tops of trees when at rest.
     To think of various kinds of birds occupying different layers of woodland is musing to some degree, but based a little on fact.  Each species of life has its own niche, and each niche has its own level in a woods, lake or a lawn.  Creatures living at different layers face reduced competition for food and shelter because each and every level in every environment is utilized.