for National Geographic News
Every spring, the bird population in North America grows by two to five billion with the arrival of neotropical migrantsbirds that winter in southern Mexico, Central America, northern South America, and the West Indies. In parts of the United States and Canada, neotropical migrants constitute more than 50 percent of nesting species.
Neotrops, as they are sometimes called, enhance the newly green spring landscape with their often-brilliant colors and beautiful songs. They include familiar species like the shade-tree-loving Baltimore oriole, striking forest denizens like the scarlet tanager, aerialists like the barn swallow, flycatchers like the eastern kingbird, and virtuoso singers like the wood thrush.
The wood warblersmembers of the tribe Paruliniform a very large group of neotrops. Of the 115 wood-warbler species in this strictly New World tribe, about 60 range north of Mexico. In my neck of the woods in Connecticut, unless I see at least 30 of them in May, when their numbers peak, I feel I haven't paid fitting tribute to the spring migration.
Drawn north this month as if by a magnet, these energized little bundles of yellow and green blow through the trees, singing constantly. No songbirds evince the power, beauty, and mystery of migration more spectacularly than the warblers. Following an ancient migratory urge, they reappear as the trees leaf out, feeding on insects. Some remain to breed; others go farther north.
Migrating warblers do most of their traveling at night. In the morning, they seem to favor migratory funnelscoastal woods, river valleys, and ridgeswhere they forage among the leaves to refuel for the next leg of their journey. On a good day, a birder can see 15 to 20 of the more than 30 species of warblers regularly found in eastern North America. Warblers also occur in the West, but the diversity of species that breed north of Mexico is richer in the East.
The migration of warblers through many of the northern states usually peaks during the second and third weeks of May. Their numbers on a given day are largely determined by the weather. Birders have all kinds of meteorological nostrums for predicting the days that will bring big flights of migrants, and for years I was among them. In May, I would become preoccupied with weather reports. When all the signs suggested that a mass warbler movement was imminent, I went to bed thinking, tomorrow is the day!
Most often, I was disappointed. Ultimately, I had to accept the idea that there was little correlation between my migration theories and what the warblers were doing. These days, like the warblers, I follow my instincts: I go birding if it feels right.
My time in the field seems to confirm that habitat destruction in breeding, wintering, and migration-stopover areas is reducing the Eastern songbird population. When I began birding 25 years ago, there were more than a few days in May when warblers poured through the woods. The overlapping songs of all the different species confused yet delighted me. Now such days are rare. I can still see 30 species by month's end, but few species occur in large numbers.
The more common warblersparula, yellow-rumped, and some eight other speciesare easy to find, and I quickly add them to my list. Next, I check off the widespread nesting species: yellow warbler, black-and-white, worm-eating, ovenbird, and yellowthroat. The hooded warbler is one of the less common nesters in southern New England, but every year I meet a few. Pine warblers, prairies, and Louisiana waterthrushes are fairly easy to find in their respective habitats.
The unpredictable warblersCape May and Tennesseeare usually scarce, but in some years, at particular locations, they can be fairly common, though they tend not to linger. Certain warblers seem to travel singly and move through quickly, providing only a small window of opportunity for birders to see them. In Connecticut, where I do most of my birding, the northern waterthrush usually falls into this category.
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