Warblers Are Back!

A yellow warbler

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They are the butterflies of the bird world, diminutive and dazzling, in colors of scarlet and orange and vivid yellow, deep, glossy blues, grays, and golds; they're striped, masked, dotted, and dashed, and their beautiful, bewitching songs—playing now in a woodland or marsh near you—are the music of renewal. It's spring! The warblers are back!

Only a few weeks ago they were crossing the Gulf of Mexico in mixed-species flocks of several thousand or more, each bird measuring just four to six inches long and weighing perhaps two ounces. Some, like the blackpoll warbler, spend the winter as far south as Peru, and in a matter of weeks reach their summer nesting grounds in Alaska, Canada, and the northeastern United States. Warblers are a strictly New World family of birds, with some 100 species in the Americas, about 40 of which are known to occur in North America. Primarily birds of forest and woodlands, warblers reach their greatest abundance and diversity across the eastern half of the United States, which supports more lush and diverse forest communities.

Warblers also have the distinction of being fairly sensitive to changes in their habitats. Some species nest on the ground, or close to it in tree stumps and low shrubs, which makes them vulnerable to predation. Many insist upon the solitude and security of large, unbroken tracts of forest. When these areas become fragmented through conversion to human uses, these species are pushed nearer to the forest edge, where their nests are at risk for sabotage by the brown-headed cowbird.

A much larger, parasitic bird, the female cowbird lays a single egg of her own in the nests of warblers and other songbirds. In some cases she will smash and devour the host birds' eggs. Even if she leaves them intact, the young warblers are usually doomed. Reared by the parents as one of their own, the young cowbird soon towers over its “siblings” and tosses or shoves them from the nest. Cowbirds as a rule are most active along forest edges, and will not venture into the deepest interiors of forests. The American redstart, ovenbird, and yellow-breasted chat are among the more frequently victimized warblers.

A couple of species are exceptionally rare due to their preference for one and only one habitat type. The Kirtland's warbler nests in five or more counties of north-central Michigan, where it finds large stands of jack pine between 6 and 20 feet tall. Another ultra-specialist is the golden-cheeked warbler. This little beauty nests only in Texas where mature Ashe juniper or “cedar brakes,” as they're known locally, are found. The female utilizes narrow strips of bark from the Ashe juniper to construct her nest. Though she may actually locate it in some other variety of tree, she relies exclusively on juniper strips for her building material.