Nantucket’s Winter Warbler -Winter 2017
by: Virginia Andrews
Warblers in the winter? We usually think of these feathered scraps of dynamic movement as treats for the eye in the spring, summer or fall. But yes, there are warblers on Nantucket in the winter.
Most species of warblers do migrate, leaving the island by the end of November. But there is one hardy representative of the family that regularly spends whole winters here: the Yellowrumped Warbler. Enduring sleet and snow, wind and fog, chills and thaws, this small bird gives birders something to enjoy amidst the grayest of gray days on the Gray Lady.
Although their winter plumage is mostly a drab blend of grays and browns, these guys have a large square patch of bright yellow right on the rump at the base of their tail. In flight, or when they perch and let their wings droop, it is as if they are displaying a tiny scrap of pure sunlight to a cold world.
They have an amazing ability to find the lee even in the worst weather. A few years ago during winter-storm Juno, when the island was blanketed in heavy, wet snow with high winds and thigh-deep drifts, these tiny birds found protected spots along pond edges where tangled vines made a shelter. Ignoring the blast, they picked their way through the bushes, gleaning whatever scraps they could find.
Originally classified by Linnaeus in 1766 they were commonly called Yellow-rumped Warblers, which is actually a more descriptive name than many species received. The scientists of the day worked from specimens in the hand rather than sightings in the bush, which made their impressions rather different.
But in the early 1900s the ornithological powers decided to split the species into two: the Myrtle Warbler in the eastern United States and the Audubon’s Warbler in the west. The two races are very similar, yet noticeably different, but will hybridize where their ranges overlap. This state of affairs lasted until 1973, when the aforementioned powers decided the differences were not great enough to warrant separation into two species. So the name was changed back to Yellow-rumped Warbler, and the Audubon’s Warbler went back to being a subspecies, along with two other more southern varieties.
At that point the “splitters” lost out to the “lumpers” once more, although there has been talk recently of splitting them back up again. To understand why this might be important, a scientific name shows a specific technical degree of relationship. It’s not to just create a bigger list. The analysis is based on things like DNA comparisons, fossil records, song and behavior, as well as breeding and wintering territory. Birders who learned the birds as Myrtle Warblers, however, sometimes still persist in calling them by the old name rather than the revised revision. It just goes to show that official nomenclature is an arcane subject, and sometimes birders make up their own lingo, no matter what the taxonomists say.
The common names of many birds would fill a dictionary all on their own, and Yellow-rumps are no different. Some island birders, perhaps with longing thoughts of a hot breakfast of pancakes after a strenuous morning of birding in the cold, simply call them “butter-butts.”
Back when Yellow-rumps were Myrtles, they were so named due to their association with the wax myrtle plant. Regardless of the name, they are unique in their ability to survive the cold. The key to wintering at the edges of the New England coast, it turns out, is the ability to digest the seeds of the bayberry and wax myrtle. Bayberries, those aromatic shrubs whose gray bark and branching growth make their clippings a pleasing contrast in winter window-box arrangements, have late-maturing waxy white berries. Early settlers used to collect the berries for candles, but it took bushels of them to make even a very little light.
But for most birds even that small coating of wax makes the seeds too indigestible. Nonetheless, they contain the protein and fats which support Tree Swallows on their migratory pit-stops and can sustain Yellow-rumps too all winter if they last. If not, the flocks will work their way south.
Massachusetts forms the northern edge of the Yellow-rump’s winter territory. It is interesting that in the 1940s there were huge flocks of Yellow-rumps along the southeast coast of the state, but few on Nantucket. They gradually increased, probably as shrub cover grew up, providing more food and shelter.
A good crop of bayberries means a good crop of Yellow-rumps, too. But they also eat other fruits, seeds and berries: juniper, woodbine, viburnum and even poison ivy. Many an inexperienced nature-lover in quest of Christmas decoration has discovered to their itchy discomfort that those other clusters of white berries that are not bayberry are also not mistletoe. But the birds don’t care. Their digestive systems can handle the highly acidic seeds and apparently find them nourishing.
Weed seeds, goldenrod, even beach grass, also provide emergency rations for a wintering warbler in an otherwise bleak landscape. With such omnivorous tastes, scattered sightings of Yellowrumps in winter have been documented as far north as Newfoundland. This is part of their summer breeding range.
As with many birds, when insects are available the warblers prefer to eat caterpillars, mosquitoes, gnats, spiders, true bugs and other invertebrates. They also feed their young insects, a high-energy diet for fast growth.
Yet despite their widespread range and relative abundance, there are still many things unknown about Yellow-rumps in the breeding season. We do know that they nest, for preference, in conifers, anywhere from four to 60 feet up. The male arrives first, and sings a sweet twitter of a tune with a little flourish at the end. He also brings some of the material with which the female makes a nest: twigs, grasses and rootlets lined with lichens and sometimes animal hair.
Among warblers they are unique in weaving feathers into the nest, using them to make a canopy to protect eggs and nestlings. Both parents feed and care for the young, and males have been observed ignoring the “don’t try to sing with your mouth full” rule when enticing the
young out on their first tentative flights away from the nest. Presumably there would be a reward for coming to dad’s song, which ornithologists delicately describe as “muted.”
Edward Howe Forbush, ornithologist for the Massachusetts Board of Agriculture from 1893 to 1928, was always looking at the economic impact of birds.
“As this warbler visits New England and breeds here in considerable numbers, it is one of our most useful birds, as 78 percent of its food consists of insects, largely injurious. They may be found where plant lice swarm upon the birches in sheltered situations, where they feed diligently until the insects are gone,” he wrote.
He makes them sound like such solid, hardworking, responsible citizens. But to watch them flitting about on a winter day is to find what looks like their fun-loving side. Often in pairs, they dart about, zipping through a stand of bayberry or scrub oak, chasing each other as if following the speedway on an invisible racetrack. They gather in flocks of a dozen to 30 or more, working over the minutiae of the landscape with fresh enthusiasm, calling their “Chip!” notes, flashing their white outer tail feathers. And, of course, their sunny, buttery butts. ///
Virginia Andrews writes “Island Bird Sightings” for The Inquirer and Mirror, Nantucket’s weekly newspaper.