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Ecosystems – FOREST BIRDS – Background
In early spring, forests of the northeast come alive with birdsong. Before the leaves come out on
the trees, the songs of the earliest arrivals echo through the bare woods. The high triplets of the
White-throated Sparrow, the Morse code tapping of the Yellow-bellied Sapsucker, the ethereal
fluting of the Hermit Thrush, are among the first to be heard. Every week thereafter, the chorus
increases in volume and variety as other birds return to the Northern Forest to breed. What
makes this region so important for songbirds?
Reaching from Maine across northern New Hampshire, Vermont, and New York, the Northern
Forest covers some 26 million acres. Within the forest are hills and valleys, wetlands and rivers,
mountaintops and coastal plains. It is a place where three major forest types come together; here
the northern boreal (spruce-fir) forest, the northern hardwood (birch-beech-maple) forest, and the
more southerly oak-hickory forest meet and overlap. Such a diversity of plant species in one
place makes it an especially rich area for birds and other wildlife species.
Forest communities have vertical structure; they are stratified into layers of vegetation. The
tallest trees form a canopy of leaves that shade the forest below. Beneath the canopy is the forest
understory where smaller trees spread their branches to catch what sunlight filters through,
aided by breezes that move the leaves this way and that. Bushy shrubs with woody stems make
up an intermediate layer of vegetation, and ferns and wildflowers form a layer of non-woody
plants close to the ground. The forest floor is covered with a layer of leaf litter and a scattering
of rotting logs.
Each layer provides homes and food for a variety of forest animals. Spiders and insects occupy
every layer of the forest, whereas forest amphibians like wood frogs, toads, and salamanders live
exclusively in or under the moist leaf litter. Forest mammals range in size from tiny shrews to
huge moose and bears. Whereas shrews spend their lives on the forest floor or tunneling under it,
bears and squirrels move from floor to canopy, using tree trunks as convenient staircases. Birds
occupy every layer of the forest too, and since they can fly, they have no trouble getting from
one layer to another.
Some of the birds that live in the Northern Forest are year-round residents. The Black-capped
Chickadee survives the northern winters by seeking shelter from the wind, storing seeds in every
available nook and cranny, traveling in flocks, and fluffing up its feathers against the cold. But
many birds are temporary residents, coming to the Northern Forest to breed and raise their young
and then leaving in the fall to return to their homes in the tropics. The number of migratory bird
species breeding in the Northern Forest is greater than anywhere else in continental North
America.
The different layers of the forest provide homes and food for many kinds of birds. Some forest
birds are ground-nesters like the American Woodcock and the Ovenbird. The woodcock probes
for earthworms with its long, flexible bill. It rocks its body while pressing the ground with its
feet to make the worms move – an amusing sight to see. Other birds, like the Wood Thrush and
Canada Warbler, occupy the shrub layer where tangled branches provide good hiding places for
nests. Birds like vireos, cuckoos and woodpeckers make their nests higher off the ground in the
forest understory. Here they are safe from most predators, though they must look out for the
Sharp-shinned Hawk that occupies this level as well. The Scarlet Tanager and Black-throated
Green Warbler are birds of the canopy, nesting and foraging high in the treetops. By occupying
different layers of the forest, these birds avoid competition with each other over resources.
One characteristic of the Northern Forest is the emergence of huge numbers of insects in the
spring. Because of the harsh winters, insects spend much of the year in a dormant state and then
emerge all at once in the spring in order to feed, find mates, and lay eggs before the short
growing season comes to an end. The abundance of insects – swarms of blackflies, countless
caterpillars, and hordes of beetle larvae, among many others – provides a plentiful source of
high-energy food for birds to feed their hungry nestlings. In addition, the longer days in the north
allow for more time to forage. It is thought that these advantages led to the evolution of
migratory behavior in many species of birds.
Whether migratory or residents, birds play an important role in the Northern Forest ecosystem
for they help to keep insect populations in control. Insects that feed on leaves and buds are
numerous and can have a damaging effect on the health of trees when their numbers become too
great. Some of these, like hairy tent caterpillars and Gypsy Moth caterpillars, are favorite prey of
birds like cuckoos and tanagers. Cuckoos consume enormous quantities of these destructive
insects, and then shed their stomach linings to get rid of the hairy spines.
While other Northern Forest woodpeckers remain through the winter, the Yellow-bellied
Sapsucker is a summer resident only. Nevertheless, it plays an important role in the Northern
Forest ecosystem. Sapsuckers are aptly named because, in addition to eating insects, they feed on
the sap of trees like maples and birches. They do this by drilling rows of small holes through the
bark of a tree into the inner bark where sugars and starches are stored so they can lick up the
sweet liquid with their long tongues. In winter, when the sap is frozen, sapsuckers migrate south.
Numerous other animals feed on the sap from sapsucker founts. Hornets looking for high-energy
food to start their colonies in the spring are attracted to this food source, as are wasps, flies, bats,
porcupines, and squirrels, to name a few. The Ruby-throated Hummingbird is thought to time its
arrival in the north with sapsucker activity. Before many spring flowers are in bloom,
hummingbirds can get a head start on nesting by drinking the tree sap. Butterflies like the
Mourning Cloak, which overwinter as adults, depend on the sap for energy when they first
emerge from their winter rest.
The sapsucker is also important because it excavates its nest in partially rotted trees. A standing
snag is a magnet for a host of other animals and sapsucker nest holes are often used in
subsequent years by other birds, mammals, or insects. Many of the cavity nesters that inhabit
sapsucker nest holes are also insect-feeders. The Sapsucker is called a “keystone” species
because it provides food and nests for numerous other animals which, in turn, help to keep the
forest insect populations in control.
Forest birds must be able to find mates, defend territories, and stay in contact with their families.
Living in this shadowy world, most forest birds use song to communicate, their voices carrying
through the dense foliage. In some species, the males display striking colors that can be seen
among the leaves. An experienced birder learns to recognize forest birds by their field marks,
special characteristics that are easy to spot and unique to each kind of bird, like a white wing-bar
or stripes on the bird’s crown. To some, learning the songs and calls is an easier way to identify
birds in the woods, for birds can be hard to see among the leaves. Keeping records of forest bird
species helps us to track the health of their populations, which is important to forest health as
well.
The Northern Forest is a habitat rich in plant and insect species, making it an ideal nesting
ground for many songbirds. Whether migratory or resident, birds play an important role in the
forest for they help to keep insect populations in control. A pleasure to see and hear, these jewels
of the forest are a valuable part of the forest ecosystem.
Suggested Reading
Kricher, John. Guide to Eastern Forests. Peterson Field Guide Series. New York: HoughtonMifflin Company, 1988.
Peterson, Roger Tory and Virginia Marie Peterson. A Field Guide to the Birds of Eastern and
Central North America. 5th ed. New York: Houghton-Mifflin Company, 2002.
Thompson, Elizabeth H., and Eric R. Sorenson. Wetland, Woodland, Wildland. Hanover, NH:
University Press of New England, 2000.
http://nationalzoo.si.edu/ConservationAndScience/MigratoryBirds/Featured_Birds
http://www.birds.cornell.edu/AllAboutBirds
http://www.vt.audubon.org
http://www.birds.cornell.edu/bfl/speciesaccts/canwar.html
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05462 (802-434-3068) www.vt.audubon.org.
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