Every spring, the bird population in North America grows by two to five billion with the arrival of neotropical migrants—birds that winter in southern Mexico, Central America, northern South America, and the West Indies.  These migrants include thrushes, vireos, swifts, tanagers, flycatchers, orioles, swallows and the warblers.   In fact, in North America, of the 650 breeding bird species, 332, or 51%, are neotropical migrants. 

In the Shenandoah National Park, this migration tends to peak in numbers by the first or second week in May.  Since 1952, the Audubon Naturalist Society has conducted a May bird census.  Counting year-round residents as well as migrants, the Society has recorded some 154 different species.  It’s a wonderful and bewildering time to identify birds by call or by sight. 

The wood warblers—members of the tribe Parulini—form a large group of these migrants. Of the 115 wood-warbler species in this strictly New World tribe, about 60 range north of Mexico.  Frequently, on a good day, 15 or more species of warblers have been found on a single morning in May.  Over 35 species have been recorded in Virginia.

Warblers are small (between 4 and 5 inches in length), active, sometimes brightly colored birds with slender, straight bills. Warbler songs are often complex and distinctive.  The different species of warblers show a variety of life styles, with some spending most of their lives high in the trees, and others foraging and breeding on, or near, the ground. The diversity of appearance between the species makes them among the most popular of the bird groups.

Warblers' nests vary from simple, tidy cups to domed structures placed in trees at a good height, in bushes, on the ground, or in niches in bank and ledges of rock. Prothonotary Warbler, however, build their nest in a cavity in a tree or in holes in man-made buildings. The Parula Warblers place their nests in a unique place, among the tufts of beard lichen.

In general, incubation is solely performed by the female.  The incubation period is usually 10-14 days.  Warblers can lay 2 to 9 eggs, but usually lay 4 or 5.  The average nestling period of warblers is 8-12 days. Both parents feed their young by carrying food in their bills.  The life span of a warbler is approximately 4-5 years.

The wood warblers are one of the defining characteristics of our Appalachian forests.