The New World warblers — that’s the avian family Parulidae — features many of the most popular and attractive songbirds in the world. As the family occurs in North America, it has a pretty uniform ecological profile: small, strongly insectivorous birds, with males often more colorful than females, often associated with tree canopies, and often highly migratory. The name “warbler” makes a Vineyard birder think of colorful sprites, nesting here or passing through en route between high-latitude breeding ranges and Neotropical wintering sites.
But since this is nature we’re talking about, of course there are exceptions. Some wood warblers are relatively short-distance migrants. In a few species, males and females look about alike. And some, repudiating their family’s fondness for treetops, spend most of their time near the ground.
Exhibiting all of these atypical traits is the palm warbler, the unusual biology of which makes it a fairly easy bird to find on the Vineyard as the calendar year winds to a close. Breeding from the northernmost Midwestern states and New England through much of Canada, this rather drably colored warbler winters largely in the Southeastern U.S. Two distinct populations transit the Vineyard as they engage in a complicated migratory pattern.
Eastern birds, both males and females, are quite yellow in spring, with a chestnut cap and chestnut streaking on the breast. Western birds at that season are duller, with yellow on their underparts largely restricted to their throats and under their tail. In fall and winter, the species is much duller, and differences are less pronounced, though the Eastern subspecies remains yellower. Even at its drabbest, a palm warbler has yellow under the tail and a habitual flicking of the tail as reliable field marks.
Oddly, Eastern breeders winter mostly to the West of their counterparts, heading South mainly through the interior, and wintering largely along the Gulf Coast. Western birds, in a diffuse, untidy migration, head roughly Southeast to winter in Florida and the Caribbean. Eastern breeders occur very sparingly on the Island in spring (they are much more common in mainland Massachusetts); in fall, it is Western birds that dominate in our coastal location.
As far as my ears can tell, the two subspecies have identical vocalizations. The song of this species is a rather disappointing trill, irregular and somehow limp in quality. The usual call note, which is usually what tips me off the presence of this species, is a flat “sup.” It sounds to me like a tiny dollop of something soft landing on the countertop.
Hardy birds, palm warblers are among the earliest spring migrants of the songbirds, passing northward in April along with pine warblers and hermit thrushes. In fall, numbers of migrants here typically peak in late September and October — but the species lingers, sometimes in good numbers, into early January and sometimes longer. Palm warblers are found most years on the Vineyard Christmas Bird Count (CBC), with counts ranging as high as 40 individuals.
This fall has been a good one for palm warblers on the Vineyard, at least where I’ve birded. I’ve encountered a lot of single birds, and several groups of a dozen or so, which seems to be about as many palm warblers as you’re likely to find together.
One group, counted quite precisely at 12 individuals, turned up in thickets at Katama in mid-November. More recently, a very active (and hence nearly uncountable) group rummaged vigorously among the spent plants of the community garden at Thimble Farm. Yet another group foraged last week on the grass around the East Chop Lighthouse in Oak Bluffs.
Foraging on open lawn is most unwarbler-like behavior, though it’s unsurprising in this peculiar species. I’ve encountered palm warblers on bare dirt smack in the middle of large, tilled farm fields, where they are surprisingly easy to mistake for that quintessential open-land bird, the American pipit. Even when around woody vegetation, palm warblers are invariably close to the ground, in bushes or the lowest tree limbs. (How they got to be called “palm warbler,” therefore, is a complete mystery to me.)
Like other warblers, a palm warbler is equipped with thin, pointed bill, optimized for winkling spiders, larvae, pupae, and small insects out of blossoms or crevices, or snatching flying insects in mid-air. Old-school ornithologists who examined the crop contents of palm warblers determined that their diet consists mostly of arthropods. But I suspect most such examinations were done in spring or summer. While palm warblers on the Vineyard in December are surely doing their best to find animal prey, they must often have to settle for seeds, and presumably they have versatile innards that can successfully process a wide range of material.
How the violent weather of the past week will affect our palm warblers is not yet clear. The snow cover, high winds, and low temperatures seem unlikely to encourage this species to hang around. Yet this is clearly a tough and resourceful bird, despite its small size, and I would be very surprised if the CBC, to be held on New Year’s Day, fails to turn up at least a few of these interesting avian visitors.