NEW WORLD WARBLERS: Parulidae

PHYSICAL CHARACTERISTICS

New World warblers are relatively small birds ranging from 4 to 7.5 inches (10 to 19 centimeters) long, although most are 4 to 5.5 inches (10 to 14 centimeters). They stand on thin, delicate-looking legs, typically have short and pointy beaks that are either slender or flat, but a few have heavier-appearing bills. Unlike all other songbirds, New World warblers have only nine primary feathers rather than ten. Many are colorful or boldly patterned, but the females' duller colors make them appear quite drab next to their striking male counterparts. The juveniles usually look much like the adult females, and males of some of the cooler-climate species also switch to a female-like, dull coloration in the fall and winter.

GEOGRAPHIC RANGE

New World warblers live in North America, South America, Central America, and the West Indies.

HABITAT

Primarily forest birds, different species of New World warblers, also known as wood warblers, may be found in everything from thick and dark forests to dry and open woods. Some have more unusual habits, and will live either in deserts or swamps.

DIET

These smallish birds spend much of their days on the move and looking for insect meals. Using their slender beaks, the birds are skillful at plucking small insects and spiders from even very tiny cracks and crevices in tree bark, between leaves, and from other hideaways. A few species add berries and seeds to their diets, and some even rely on those food sources to survive snowy winters. Most New World warblers scrounge for food on the ground or on plants or trees.

BEHAVIOR AND REPRODUCTION

Perhaps the most characteristic behavior, and the most frustrating for birders who are trying to spy one of the birds through their binoculars, is the nearly constant motion of New World warblers. No sooner do they land on a tree branch than they are off again to new destination. For this reason, plus the sometimes-dense woods that hide them from view, most birders in the field recognize different species of warblers not by sight but by their songs. Only the males sing, except in a few species when the females also join the chorus. Many species have lovely, bright songs, but others are merely loud, and some have quite quiet, scratchy voices that sound more like insects than birds. Each song, however, is characteristic to a particular species. By learning their songs, birders can walk into the woods and know which species are there without ever seeing a single bird. As in other birds, both males and females also communicate through various quick cheeps and chips, some of which may also be very distinctive to a particular species.

THE THREAT FROM COWBIRDS

Warbler numbers are declining in many areas due to the much larger brown-headed cowbird. Unlike a predator that directly attacks and kills warblers or eats their eggs, the cowbird's threat comes from its breeding habits. Instead of laying eggs in its own nest and raising its own young, the cowbird lays its eggs in other birds' nests and leaves the parenting to the adoptive parents. Unfortunately for the warbler, the small birds do not recognize the foreign egg and raise it as their own. Cowbird eggs are larger and typically hatch a bit earlier, which gives the young cowbird a distinct advantage over its smaller nest mates. Sometimes, the cowbird pushes the others out of the nest and to their death, but even the baby warblers that remain often miss out on feedings from their mother as the larger cowbird can push its beak to the front for meals. As a result, young warblers starve to death. The behavior of the cowbird is known as brood parasitism, because it actually becomes a parasite on the mother warbler's family, or brood.

Most of the species that summer in North America migrate far south for the winter, sometimes flying 3,000 miles (4,800 kilometers) or more to a warm, sunny location. Usually, the birds leave their northern haunts in the fall, long before bitter temperatures settle in. Fall migration flocks can number in the thousands and include many different species of birds. The flocks travel from sunset to sunup. On a night with a full moon, a careful observer can sometimes spot the flocks as silhouettes against the surface of the moon. The birds return the following spring.

The male warblers usually arrive in the spring shortly before the females. The head start allows the males to set up their breeding territories. As the females arrive, the males begin singing to entice a mate. Once a pair forms, the warblers go about making a nest and preparing for egg laying. Some species make their typically cup-shaped nests on the ground, others in shrubs, and some high in the trees. A typical clutch is three or four eggs, which are usually white with irregular spots. The female sits on the eggs while the male dashes about finding food and bringing it back to her. When the eggs hatch nearly two weeks later, the mother helps the father find and deliver food to the babies. The young grow quickly, and are nearly adult weight by the time they are ten days old. At that point, they test their wings and leave the nest, but they don't go far. The parents continue to feed them, but since the young are no longer together in the nest, the mother generally takes care half the offspring, and the male feeds the other half. After a few weeks, the parents stop their care and the young birds are on their own.

NEW WORLD WARBLERS AND PEOPLE

Warblers have a special place in the hearts of birders and anyone else who enjoys a lilting song or a glimpse of color while walking outdoors. Some North American communities even have festivals to herald the return of the small birds each spring.

CONSERVATION STATUS

According to the Red List of the World Conservation Union (IUCN), three species are Critically Endangered, facing an extremely high risk of extinction; five are Endangered, facing a very high risk of extinction; seven are Vulnerable, facing a high risk of extinction; and eight are Near Threatened, in danger of becoming threatened with extinction. The U.S. Fish and Wildlife Service lists five endangered species: Bachman's warbler, Barbados yellow warbler, golden-cheeked warbler, Kirtland's warbler, and Semper's warbler. For the most part, a small breeding range and shrinking habitat are the primary threats to these species. When people undertake habitat-preservation efforts, however, the species generally respond favorably.

YELLOW-BREASTED CHAT (Icteria virens): SPECIES ACCOUNTS

Physical characteristics: The largest of the New World warblers, both male and female yellow-breasted chats have an olive-colored back, yellow throat and breast, and white belly. Eyes are ringed in white, and the blackish face has white stripes. The beak is larger and appears heavier than most other warblers. The bird reaches about 7.5 inches (19 centimeters) long.

Geographic range: Its breeding grounds are in southern Canada, the United States, and northern and eastern Mexico, and its wintering grounds in Central America.

Habitat: Usually found near water, where it typically remains hidden from sight in thick brush.

Diet: It mostly eats insects, but also snacks on berries on occasion.

Behavior and reproduction: This bird can often be heard flying and otherwise pushing its way through brambles and thickets. In addition to its typical daytime activities, this warbler also sometimes sings at night. The song is a mixture of caws, gobbles, and a few singsong phrases. Unlike other nesting pairs of warblers that are quite territorial, several chat pairs will sometimes share a single nesting site. Their cup-shaped nests are tucked in thick brush. Eggs, which typically number up to six, are speckled with brown and purple.

Yellow-breasted chats and people: Seldom seen, but often heard, chats add to nature's outdoor symphony.

Conservation status: This species is not threatened. ∎

BLACK-AND-WHITE WARBLER (Mniotilta varia): SPECIES ACCOUNTS

Physical characteristics: An appropriately named bird, this warbler has black and white stripes over much of its body. A male has a black patch on his throat, and a female has a grayish white patch on hers. Size ranges from about 4.5 to 5.5 inches (11.4 to 14 centimeters), and the bird weighs 0.3 to 0.5 ounces (9 to 15 grams).

Geographic range: The black-and-white warbler spends the warmer months in Canada and the eastern half of the United States, then migrates for the winter months to southern U.S., Mexico, West Indies, Central America, and northeastern South America.

Habitat: They tend to live in areas with numerous large trees, as well as a tall, thick understory. The trees provide a place for finding food, and the thickets provide a place to hide.

Diet: These birds eat caterpillars, flies, beetles, and other insects; and spiders.

Behavior and reproduction: It spends much of its time creeping up tree trunks in search of small insects and other creatures in the little openings and cracks in the bark. Its song is a quiet and short peeping phrase. These warblers migrate north a bit earlier than most other warblers, and soon begin breeding. They usually build their nests on the ground, although a few construct theirs in a hidden spot just up the side of a tree trunk, and then use some carefully placed leaves to camouflage the nest. Each pair has four or five eggs that hatch in ten days. Predation on the ground nests by dogs, cats, raccoons, and other animals is common.

Black-and-white warblers and people: As with most warblers, its primary benefit to people is its beauty.

Conservation status: This bird is not threatened. ∎

KIRTLAND'S WARBLER (Dendroica kirtlandii): SPECIES ACCOUNTS

Physical characteristics: This bird reaches about 6 inches (15.3 centimeters) and 0.5 ounces (15 grams). It has a dark, bluish gray back and head, white eye ring, and a gray-specked, yellow throat and belly. Males are slightly more vividly colored than females, and have a blackish stripe on the face.

Geographic range: This bird summers in Michigan, and winters in the Bahamas.

Habitat: Its summertime home is primarily forests of jack pine trees, usually preferring forests with many young trees whose branches dip close to the ground and provide cover for their ground nests.

Diet: Kirtland's warblers eat insects, and occasionally berries, or pine needles.

Behavior and reproduction: Although the warbler is quite rare, a birder who knows where to look can readily see them flying between pine trees and nabbing insects in midair. In late spring to early summer, Kirtland's warblers build small cup-shaped nests on the ground under low-lying pine branches. Broods typically number four or five eggs. The eggs hatch in about two weeks, and the young birds leave the nest about a week and a half later. One of greatest dangers to the birds comes not from direct predation, but from the wily brown-headed cowbird, which lays its eggs in the warbler's nest. The warbler cares for the cowbird young, often neglecting its own chicks.

Kirtland's warblers and people: People from around the world come to Michigan in the spring and summer to spot this bi-colored bird. Kirtland Community College, located in the breeding area, holds an annual festival in the bird's honor.

Conservation status: The need for the Kirtland's warbler to breed in young jack pine stands in northern Michigan has contributed to its low numbers. In response, efforts to improve its habitat have occurred, and the number of breeding pairs is increasing. The U.S. Fish and Wildlife Service currently defines this species as endangered, but its ranking on the Red List has improved from Endangered in 1994 to Vulnerable in 2000. ∎

FOR MORE INFORMATION

Bent, Arthur C. Life Histories of North American Wood Warblers. New York: Dover Publications, Inc., 1963.

Cassidy, James, ed. Book of North American Birds. New York: The Reader's Digest Association, Inc., 1990.

Dock Jr., George. "Yellow-Breasted Chat." In Audubon's Birds of America. New York: Harry N. Abrams, Inc., 1979.

Ehrlich, Paul R., David S. Dobkin, and Darryl Wheye. The Birder's Handbook. New York: Simon and Schuster, Inc. (Fireside Books), 1988.

Garrett, Kimball L., and John B. Dunning Jr. "Wood-Warblers." In The Sibley Guide to Bird Life and Behavior, edited by Chris Elphick, John B. Dunning Jr., and David Allen Sibley. New York: Alfred A. Knopf, 2001.

Peterson, Roger Tory. A Field Guide to the Birds of Eastern and Central North America. Boston: Houghton Mifflin Co., 1980.

Periodicals:

Berger, Cynthia. "Exposed: Secret Lives of Warblers." National Wildlife 23 (2000): 46–52.

Lichtenstein, G., and S. G. Sealy. "Nestling Competition, Rather than Supernormal Stimulus, Explains the Success of Parasitic Brown-headed Cowbird Chicks in Yellow Warbler Nests." Proceedings of the Royal Society of London 265, no. 1392 (2000): 249–254.

Price, T., H.L. Gibbs, L. de Sousa, and A. D. Richman. "Different Timing of the Adaptive Radiations of North American and Asian Warblers." Proceedings of the Royal Society of London 265 (1998): 1969–1975.

Weidensaul, Scott. "Jewels in the Treetops." Country Journal 23 (1996): 58–61.

Web sites:

Endangered Species Program, U.S. Fish & Wildlife Service. http://endangered.fws.gov/ (accessed on May 5, 2004).

IUCN Red List of Threatened Species—Species information. http://www.redlist.org (accessed on May 29, 2004).