Palm Warbler

A better name for this species would perhaps be “bog” warbler, since it nests primarily in spruce and tamarack bogs. It is only one of two warblers in its genus to nest on the ground, typically building its nest into sphagnum moss at the base of a small conifer. Although an uncommon (but increasing, see below) breeder in New Hampshire, it is one of our more common migrants, and among the first warblers to arrive in spring and latest to leave in fall. The “palm” in its name comes from the wintering grounds, which include the southeastern United States, Greater Antilles, and parts of Central America. During the winter it can frequently be seen hopping around on beaches or lawns, apparently oblivious to people. It is at this time of year that another unusual aspect of the species is readily apparent: it is the only warbler in its genus to forage almost exclusively on the ground.

The history of the Palm Warbler in New Hampshire is a fascinating one. It was not known to breed here until 1955, when a nesting pair was discovered near Lake Umbagog. For the next several decades the upper Androscoggin Valley was the only place to find this rare breeder in the state, but that began to change in the late 1990s. During a roughly ten-year period, several new breeding sites were located, including some well south of the White Mountains, and numbers increased in the species North Country stronghold. Similar dramatic range expansions were documented in New York, Vermont, and Maine during this same time. Such a significant southward invasion is particularly inexplicable for a northern species like the Palm Warbler, and seemingly is counter to what one would predict in the face of climate change.

There are two distinct subspecies of Palm Warbler, both of which occur in New Hampshire. The one that breeds here is the “Yellow Palm Warbler,” which as its name implies has bright yellow underparts. From the Great Lakes west is the “Western Palm Warbler,” which is generally much duller brown although it still has a yellowish rump and undertail coverts. The western subspecies occurs here during fall migration and is the more likely form later in the season. An unusual feature of these two subspecies is that they cross over each other during migration. The yellow version heads southwest to winter along the coast of the Gulf of Mexico, while the western one moves southeast to the Atlantic coast and islands in the Caribbean.