Least and semipalmated sandpipers
Least and semipalmated sandpipers
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By late summer we begin seeing juvenile birds in various stages of development. Changes in plumage and other physical characteristics occur rapidly as young birds progress from hatchling status through nestling and fledgling phases. Birds in juvenile plumages often look a bit scruffy or incomplete as distinguishing details, such as wings and tail feathers, mature. Probably to avoid detection by predators, juvenile songbirds often appear duller and more camouflaged by cryptic color patterns. These early plumages generally last less than four weeks, after which birds generally begin to resemble adults.

Juveniles’ body proportions may appear a bit “off” too, as they grow into their maturing bodies. Young birds may have oversized bills that look too big for their head. Some species retain the colorful or fleshy corners to the mouth (the “gape flange” is an important feature during wide-mouthed begging sessions of nestlings). Legs and feet may appear too large for the body. This is exemplified in precocial species, such as ruffed grouse and piping plovers that must scramble to fend for themselves shortly after hatching. Being fleet footed on beaches and wooded habitats is essential for survival.

Sometimes physical actions highlight juvenile status, as fledglings may appear slow, dopey or a bit clumsy as they flit through cover. Youngsters often reveal themselves by begging vocalizations or wing-waving action as they shadow their parents. Fledglings typically make repetitive chitting sounds to maintain visual contact and attention from parents. Perhaps the surest way of identifying any species of young birds is to witness an adult parent feeding them. Sustained attention on the begging or quivering youngster while an adult delivers food often pays dividends.

There is one case where a juvenile species is easy to recognize: brown-headed cowbird chicks. Since female cowbirds lay eggs in nests of unsuspecting host species, the “parent” of a cowbird could be a warbler, sparrow or other songbird. The panhandling cowbird chick is often larger than the host parents that work diligently to provide food. This size disparity makes for some fascinating behavior watching as the viewer also registers dual sightings simultaneously.

Should we consider some ways to distinguish migrant adult shorebirds from juveniles? If so, disregard all I’ve said regarding songbirds. For tundra-nesting shorebirds, fall plumages of juveniles are actually brighter and more vividly marked than the adult populations that have already passed through. Shorebird migration happens in incremental stages. Beginning in mid-July, adult shorebirds move southward. Those early-passage adults are wearing worn and faded coats of feathers; in some cases, a few gray winter feathers may have emerged on their backs.

Currently, flocks of energetic bright-backed juvenile sandpipers are working the low-tide mudflats of Thomaston Harbor, probing for marine invertebrates. During high-tide cycles these same flocks roost at local shorelines and marshes such as Weskeag Marsh. Their typical routines are divided between vigorous feeding and intermittent roosting sessions that conserve energy and build fat reserves. At the roosts, birds spend time preening or resting on one leg with heads tucked into body feathers to diminish heat loss. Within a two-week period, they will double their weight before starting the next leg of their extended southern journey.

Juvenile shorebirds of several species show clean, crisp markings consisting of dark-centered back feathers outlined by pale edges. This creates a scaly or scalloped appearance that lasts just a few weeks. These includ se short-billed dowitchers and some of the smaller sandpipers such as least and semipalmated.