The three basic strategies used by warm-blooding animals (mammals and birds) for surviving the rigors of winter are hibernation, migration, and adoption of methods to “tough it out.” By far, most of these animals in North America follow the third strategy. Very few animals hibernate. Depending on how broadly one defines hibernation, our forest representatives include ground hogs, jumping mice, numerous bats, and, to a lesser extent, chipmunks and black bear.
Of our migratory species, birds are the most numerous. In North America, more than half of our breeding birds migrate (332 of 650 species). Certain bat species also migrate, including three of the Appalachians’ 12 native species, as well as the famous Mexican free-tailed bats of Carlsbad Caverns and Congress Bridge in San Antonio.
Winter provides the Shenandoah National Park the opportunity to be the host of many northern nesting birds. These seasonal guests include northern juncos, brown creepers, red-breasted nuthatches, golden-crowned kinglets, yellow-bellied sapsuckers, short-eared owls, pine siskins, purple finch, sparrows (white-throated, American tree, and fox), rough-legged hawks, and a few others. Many of these can be found breeding in the Appalachian plateau of West Virginia and North Carolina, where it is of higher elevation and cooler, but normally not in our Park. Contrary to conventional thought, we do have robins in winter. There is a shift in robin populations in the fall, so that our winter robins have bred in New York and Pennsylvania while our breeding stock is sunning down in the Carolinas. If you spend much time in the woods, you will see them in large flocks in the treetops. Unlike most birds, they continue to call throughout the winter. Just don’t look for them in your front yard until spring, when the worms have come back to the surface. In fact, the Indians call the March full moon the worm moon, for this reason.
Birding in the winter is a case of feast or famine. It’s not uncommon to hike most of the day and practically see no birds at all, then, suddenly, you may notice the trees and shrubs around you are alive with a mixed flock of many bird species. If you’re in the woods, you will probably identify such species as Carolina chickadees, tufted titmice, golden-crowned kinglets, brown creepers, downy woodpeckers and white-breasted nuthatches.
If you watch closely, you will probably find that these winter flocks are led by either the chickadees or titmice. These two nuclear species within the mixed flock average six birds and form around a dominant pair, normally that mated the previous season in that general area. Other members of the population may be juveniles of the dominant pair or other stray adults and juveniles. They will remain within a general range throughout the winter that includes their breeding site as well as several good feeding sites that they will return to numerous times. In fact, some flocks will rotate among four or five favorite feeding sites on a daily basis. It is not uncommon for these chickadee and titmice flocks to return to the same roosting site every night during the winter season.
It has been suggested that the other species tag along with the chickadees and titmice because the vocalizations of these two species enable the others to maintain their small groups. This is especially beneficial for the very small kinglets, which often can survive the winter cold only by huddling in tree cavities overnight. By staying together by listening to the vociferous chickadees and titmice, they are assured of overnight companions. Also, the nuclear chickadees and titmice, being year-round residents, know the good feeding areas. Thus, the winter guests benefit from this knowledge.
Anther benefit of winter flocks is that there is safety in large numbers. By having many eyes around, individual birds can spend more time eating and less time looking for predators. From the perspective of the nuthatch or downy woodpecker, flocking with the very alert and excitable chickadees and titmice increases their awareness of incoming predators and thus adds to their chances of winter survival.
Of all the birds that reside in our winter forests, the golden-crowned kinglet must have the toughest life. To start with, it is our smallest winter bird; smaller than our summer warblers, weighing in at two ounces and a total head to tip of tail length of 3 ½”. This large surface area to volume ratio makes heat loss a major issue. To make things more difficult, the kinglet is a strict insectivore, passing over the available seed supply for the harder to find over-wintering insect eggs. If life for this tiny insectivore wasn’t already hard enough, now we have introduced the hemlock woolly adelgid. This aphid-like insect has been killing the hemlock groves throughout the kinglet’s wintering range, effectively eliminating its favorite habitat for both food and shelter. Look for the golden-crowned kinglet flitting about in these hemlock groves in small, lose groups, often with titmice and chickadees, and listen for it’s weak high-pitched trill that these birds use to communicate amongst themselves.