It is late afternoon on May Day, and the masked bandit is standing on the stoop of our veranda door. He looks around alertly as I speak to him.
“What are you doing here?” I ask.
He doesn’t seem inclined to move or to answer. After all, he’s only a songbird who sings “witchedy, witchedy,” and he doesn’t even honor me with his song.
Instead, he flies up along the edge of the house as if he is looking for insects. Then he lands in front of the living room window, and I wonder if he has seen his reflection in the glass. Or had he previously noticed his reflection in the storm door and wished to fight his rival.
He flies back to that door and looks as if he wants to go inside. Finally, he flies up to the transom above the door and pecks at his reflection. Apparently, he does see a rival in his reflection, but he is not as persistent as towhees and cardinals, both of which have tapped for hours and many weeks on our windows.
After a few minutes, he flies back down to the stoop and then suddenly silently flies away. That is the last we see of him around our home, although we hear plenty from him and other common yellowthroats throughout the breeding season. Still, I am left with more questions than answers about his visit and readily admit that despite watching birds for most of my life, I am still puzzled by much of their behavior.
The name of this warbler “common” describes its ubiquitous presence during the nesting season in most of North America from every province in Canada to western Mexico, and its position as the number one or possibly two most common breeding warbler in Pennsylvania. Its “yellowthroat” refers to its bright yellow throat, chin and breast.
But I prefer my name for the male common yellowthroat, the “masked bandit” because of his distinctive black mask outlined above in white which separates his black forehead and mask from his olive head, back, and wings. The female is plain olive with a pale yellow chin, throat, and breast, ideal for blending into the shrubby habitat where she builds her nest and cares for her young.
Ornithologists have distinguished 15 subspecies of common yellowthroats based mostly on slight variations in their color, size, wing and tail proportions. Our common yellowthroat Geothlypis trichas trichas, once split into the northern and Maryland yellowthroats, has now been combined and ranges from Newfoundland west through Ontario and Minnesota, south to east Texas and east to the Appalachians and includes the rest of eastern United States and Canada, but excludes the coastal Carolinas and most of Georgia and Alabama (subspecies typhicola) and Florida (ignota).
First collected in Maryland, the common yellowthroat was one of the first birds described from the New World by the pioneering Swedish taxonomist Carl Linnaeus back in 1766. He named it Geothlypis meaning “a kind of finch of the earth” and trichas meaning “a thrush,” because European warblers hadn’t been classified at that time. Even later, taxonomists discovered that European warblers are not related to New World warblers, hence the designation of our warblers as “wood warblers.”
Not all New World warblers favor woods including the common yellowthroat. It prefers dry or wet shrubby growth in weedy fields and marshes on both their breeding and wintering grounds. Since we have a weedy wetland and an upland dry weedy field, our land supports several breeding yellowthroats. I suspect our veranda visitor was claiming the overgrown beginnings of our stream as his territory.
Male common yellowthroats arrive in our area a week ahead of the females, usually in late April or early May and vigorously defend their territory from encroaching males, although real fighting with each other increases with the arrival of females.
The females signal they are ready for breeding by fluttering their wings and tail and chipping quickly. Once they pair up, males follow their mates closely, probably hoping to prevent the sometimes polyandrous females from copulating with other males.
Nest building by females begins almost immediately after they choose a site on or near the heavily vegetated ground, and their nests are supported by sedges and grasses, cattails, briars or reeds. Finding their nests is difficult because they are well concealed. In addition, both males and females are extremely secretive, sneaking through the underbrush on pathways hidden by thick vegetation when a human approaches a female sitting on her nest or later, after the eggs hatch, when they are feeding nestlings.
Females lay on average four white eggs spotted or blotched gray, reddish-brown, lilac, or black. They incubate the eggs 12 days, and their nestlings are totally helpless when they hatch. But they grow amazingly fast and while they are able to fledge at eight days by climbing over the edge of their nests and moving into heavy vegetation, most wait until they are 12 days old to fledge.
Both parents have been feeding them and continue to do so for three weeks while the fledglings strengthen their wings and move into nearby woods or thickets. In Pennsylvania common yellowthroats are forest edge species and nest building begins here the first week in May. The Second Atlas of Breeding Birds in Pennsylvania observers reported seeing young through July which suggests that they may have two broods.
Common yellowthroats are wholly insectivorous, eating beetles, grubs, the larvae and adults of moths and butterflies, flies, ants, spiders, plant lice, leaf hoppers and leaf rollers, gleaning food for themselves and their young from the ground or shrubbery. As long ago as 1907, E.H. Forbush in Massachusetts watched a male common yellowthroat eat 52 gypsy moth larvae before flying away and concluded that the yellowthroat was an efficient enemy of the pest. He also saw a yellowthroat eat 89 aphids in a minute. Another researcher found that yellowthroats consumed large numbers of cankerworms in orchards.
Both eggs and nestlings are preyed on probably by snakes, mice, chipmunks, skunks, opossums, and raccoons and adults are occasionally caught by loggerhead shrikes, merlins, American kestrels and northern harriers.
But the parasitizing of their nests by brown-headed cowbirds may be the greatest threat to yellowthroats. One study, of 20 nests with cowbird eggs, found that only three produced young yellowthroats. On the other hand, some yellowthroats seem to recognize cowbird eggs or notice that their own eggs have been removed and replaced by those of cowbirds, and they build a second nest or even a third one on top of the parasitized nest.
By the third week of August some common yellowthroats in Pennsylvania start their migration south, although the peak is during the second and third weeks of September. Flying through the night, adults and immature birds head for the Caribbean islands or Central America all the way to Panama, seeking the same shrubby vegetation to spend the winter. However, at least those wintering in Quintana Roo, Mexico, are segregated by sex with males preferring second-growth scrub and natural open habitat and the females more common in open pastures and fields according to a 1990 study by A.L. Ornat and R. Greenberg.
Like many songbirds, even those as numerous as the common yellowthroat, there have been no long-term studies of their breeding biology or behavior, but recently there has been interest in their song and singing behavior. Even though I’ve heard only their “witchedy, witchedy” song and scolding notes, it turns out that their song varies in the number of notes per phrase, enough that their mates can distinguish them from other males.
Male nestlings learn their song by listening to adult male yellowthroats, but, in some cases, both in captivity and in the wild, they learn other songs as well. One wild yellowthroat in Massachusetts sang his own song in addition to a perfect rendition of a chestnut-sided warbler’s song. And a captive yellowthroat learned a yellow warbler’s song.
Thinking back to the many male common yellowthroats I’ve encountered over the years, including our veranda visitor, I must agree with Alfred Otto Gross’s description of the birds he spent hours watching from a blind decades ago. …”one is impressed with the vigorous personality of the male. He nervously raises his alarm with a variety of scolding, interrogative chirps and chattering notes and his dark inquisitive eyes sparkle with excitement through the black masks.”