greenthroatedwarbler

Male black-throated green warbler.

Last weekend I saw a lot of yellow-rumped warblers at Langenau Forest on the ridge between Pleasant Lake in New London and NH Rt. 4A in Wilmot. When I was younger, migrating flocks of warblers were often referred to as “waves,” because it felt like they were breaking over you when you stood under them and watched. It was possible to see dozens of warblers of a single species in one tree, as if it was full of animated bright-colored fruit.

It has been many years since I have seen that sort of concentration of migrating birdlife, but this flight of yellow-rumpeds came close. I saw at least one ruby-crowned kinglet mixed into this flock, a not unusual combination. These are the earlier woodland migrants, joining the chickadees and purple finches that have been here all winter.

While the yellow-rumped warbler winters as far north as southern New England, most warbler species spend the colder months in the Caribbean, Central and northern South America and Mexico, with a few lingering along the Gulf Coast and in Florida. The black-throated green warbler (Setophaga virens) is one of these, migrating south in the fall to all of these places, depending on where they spend the breeding season.

The spring migration of the black-throated green is called “complex and extended” by Jon Dunn and Kimball Garrett in their 1997 Warblers field guide. Most migrate across the Gulf of Mexico, but some come up through Florida and a very few fly overland across the Rio Grande in Texas, which is unusual for eastern wood warblers. They begin arriving early for Neotropical winterers with some spotted in late March as far north as Massachusetts and southern Ontario.

The wave breaks across eastern North America through April and May with the peak in the Great Lakes and New England in the second and third weeks of May, according to Dunn and Garrett. This morning I heard an early arriving member of this wave. Amid the piercing calls of a flock of resident titmice I picked out the quiet beginnings of the easily recognizable song of this species: zee zee zee zee zo zeet (Sibley’s rendering).

While the black-throated blue warbler (Dendroica caerulescens) nests right near my cabin, S. virens remains in the forest and I hear him singing through the spring and early summer at a distance. While the black-throated blue prefers early successional habitats, the black-throated green nests in second-growth forests. The common characteristic of all its preferred habitats is a multi-layered structure; it is found where there are well developed layers of shrubs and smaller trees beneath the canopy. That is, over-browsing by deer may cause this species to pass over your woodlot.

Per Dunn and Garrett, in New Hampshire the greatest densities of this species are found in purely deciduous forest. Over much of its range, however, it is associated with various types of conifer, hemlock in the Appalachians and white pine in the northern part of its range. Arthur Cleveland Bent (1953) said in Massachusetts few white pines were free of them. An isolated population along the mid-Atlantic coast (S. v. waynei) is found in cypress and white cedar swamps.

In The Warblers of North America by Ludlow Griscom and Alexander Sprunt Jr. and others (1957), Sprunt and A.E. Allin call this species a “high ranger” that is “more often heard than seen.” But it is also not shy, and it can be “psshed” closer to ground level, if you are patient. The male in particular will make his way down from the canopy to investigate an odd sound issuing from a still observer, but he will not linger once he has determined that you are not an intruder. This species is known for vigorously driving others of its kind and other small birds out of his breeding territory.

Sprunt and Allin note that it is oddly selective about who it considers dangerous. They cite reports in Bent (Life Histories of North American Wood Warblers, Part 1) that document the male and female S. virens attacking other warbler species and completely ignoring chickadees and red squirrels. A foraging red-eyed vireo was observed to change its course after a single warning note.

Although difficult to see, it sings persistently, even in the middle of the day, and is therefore less difficult to track down than some other warbler species. Margaret and Blaine Nice (1932) made a study of a black-throated green warbler on the nest in central Massachusetts (she was

from Amherst) and found one warbler “gave 466 songs in a single hour and more than 14,000 in the 94 hours of observation.”

When you do see it, it is a treat. The male S. virens has a bright olive-green unlined back, gray wings with two prominent white wing bars and a long gray tail that flashes white at its outer edges. The top of the head is olive green but the face is bright yellow with an olive patch behind the eye. The black of the throat extends in streaks down the sides, and there are patches of yellow wash on the breast and near the base of the tail. The female is quite similar, but her throat is white and she lacks the yellow wash on the breast.

By early June these birds will be settled into their breeding territories from here to Saskatewan and will occupy their territories until late August or early September. In the third week of June there will be four or five eggs in a cup-shaped nest on the horizontal limb of a tree well away from the trunk. And they will sing. A lot.

Bill Chaisson has been a birdwatcher for over 50 years. He is a former managing editor of the Eagle Times. He now lives and works in Wilmot. Contact him at wpchaisson@gmail.com

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