Thistle-Birds

In August our weedy First Field is alive with singing American goldfinches. Although most songbirds are finishing their parental duties by then, American goldfinches have barely begun.

A male American goldfinch among thistles at the John Heinz National Wildlife Refuge at Tinicum, PA

A male American goldfinch among thistles at the John Heinz National Wildlife Refuge at Tinicum, PA (Photo by Jim, the Photographer, on Flickr, Creative Commons license)

Their preference for thistle and other seeds may be one reason they wait until midsummer when the seeds are mature, because they line their nests with thistle, milkweed or burdock down and feed their nestlings a slurry of those regurgitated seeds, instead of insects, which are favored by spring-breeding birds.

Another reason may be the length and intensity of goldfinches unique prenuptial body molt in early spring. The dramatic change of the olive-buff males to vibrant gold bodies and black caps, which set off their black-and-white wings, never fails to dazzle me every April.

But knowing they do not breed until midsummer, I am also surprised that they sing as lustily as other species beginning in early spring. Some researchers believe that they form pair bonds in late winter flocks or as soon as both sexes arrive on their breeding grounds.

A female American goldfinch

A female American goldfinch (Photo by Eric Bégin on Flickr, Creative Commons license)

On the other hand, males need to try harder for mates because for every 1.6 males, there is only one female, so first-year males have a difficult time acquiring a mate. Thus, while goldfinches are mostly monogamous, at least 15% of females mate with a second mate especially if they have a second brood.

Back in the years 1979 until 1985, Alex L. Middleton, of the University of Guelph in Ontario, was watching nests of goldfinches he had color-banded on the university grounds. That was when he made, for the first time in ornithological history, the observation that the goldfinch father of the first brood was not always the father of the second one, proving that regular and recurring classical polyandry was occurring in a passerine species.

A male American goldfinch at the John Heinz National Wildlife Refuge at Tinicum, PA

A male American goldfinch at the John Heinz National Wildlife Refuge at Tinicum, PA (Photo by Jim, the Photographer, on Flickr, Creative Commons license)

During his study, he found five cases of polyandry and concluded that even though only a few females practiced it, they had more than seven fledglings a season compared with slightly over three for “faithful” females. In addition, the polyandrous females were older, experienced birds that preferred to breed with older males because of their experience and their physiological fitness which enabled them to start breeding a week ahead of younger males.

But a younger male sometimes attached itself to the breeding pair and when the first male was still busy feeding his first brood and his mate was already building a second nest, the surplus male bred with the female. Since then, researchers have been finding that many so-called monogamous songbirds are not as faithful as they were once portrayed with both males and females sneaking extra-pair copulations.

A crowd of American goldfinches on a Nyjer thistle feeder in Danville, PA

A crowd of American goldfinches on a Nyjer thistle feeder in Danville, PA (Photo by fishhawk on Flickr, Creative Commons license)

Last April our feeders were crowded with males in the midst of molting and far fewer females. Whether they were migrant males and females or those that had been with us all winter was impossible to tell, because we had had on average 12 goldfinches at a time on our feeders throughout the colder months.

Here in Pennsylvania they migrate through the state from late March until late May, although their peak migration is from the fourth week in April to the second week in May. Many are coming from as far south as the Gulf states and Florida in the United States and central Mexico, but they do wander in large flocks wherever there is ample food, even in winter. They breed from southern Canada through most of the United States with the exception of the southwest and along the Gulf Coast.

American goldfinches rarely nest in Pennsylvania before July 5 and nests with eggs are found here through the end of August. However, the earliest confirmed breeding in the commonwealth, according to the Second Atlas of Breeding Birds in Pennsylvania, was that of a bird carrying nesting material on May 2 and the latest was of parents feeding young on October 14.

The female selects the nest site, often in a wet corner of a brushy pasture such as our First Field, and constructs it in the fork of a sapling or shrub, anywhere from one to 33 feet above the ground. Three dogwood species and numerous hawthorn and willow species are special favorites.

She takes at least four days to build her tightly constructed nest with walls so thick that the nest can hold water. Sometimes this leads to disaster during heavy rainstorms when unattended nestlings drown.

A male American goldfinch feeding a female on May 4, 2007

A male American goldfinch feeding a female on May 4, 2007 (Photo by Doug Greenberg on Flickr, Creative Commons license)

One unusual nest was found hanging from a broken cornstalk in a cornfield near Hamburg, Pennsylvania on September 24, 2008. It was turned on its side on the stalk and was attached by spider silk and plant fibers. Lined with thistle down, it contained a single egg. Even though American goldfinches have been known to nest in as many as 87 plant species, this was the first nesting on a cornstalk confirmed with a photograph. But after watching for a couple days and seeing no goldfinches nearby, the researchers concluded that the nest had been abandoned several weeks before, especially since the nest looked a bit tattered.

Once their nest is finished, the pair leaves the area for several days, maybe to deter predators such as eastern garter snakes, blue jays, and short-tailed weasels. Then the female lays four to six very pale bluish-white eggs and she sits on the nest 95% of the time incubating the eggs while her mate supplies almost all of her food.

The male often sings and flies high above the nest site, checking up on whether his mate needs food. When he hears her soft teeteeteetee hunger call, he drops down near the nest. Then she furtively hops through the underbrush to him to receive her meal.

After 12 to 14 days, the eggs hatch and she broods the young while the male continues feeding her on the nest. She in turn feeds the chicks, but after four days she leaves the nest. Then both parents feed their nestlings by regurgitating a sticky, half solid mass of seeds, including those of sunflower, thistle, burdock, dandelion, chicory, aster and goldenrod, all of which thrive in overgrown pastures.

The nestlings are quiet during their first week in the nest, but by the second week they are active and noisy and fledge anywhere from 12 to 17 days of age. They are dependent on their parents for three more weeks while they learn what to eat and where to find it.

Once they are independent, the young birds join flocks of adults that increase in size during late summer and early autumn. It is then that goldfinches, once they finish breeding, engage in their second molt of the season that lasts as long as 75 days.

They also wander the countryside in search of food. Their choices have led to a variety of nicknames such as “catnip-bird,” “beet-bird,” “lettuce-bird,” and “thistle-bird,” that attest to their liking of both garden and wild plant seeds. “Wild-canary” and “shiner” are tributes to the male’s golden plumage. In addition, their genus name, Carduelis, is Latin for “thistle” and their species name, tristis, means sad, referring to their plaintive calls. Their song, which is unusually long, is both rambling and warbling.

An American goldfinch in Chester County, PA

An American goldfinch in Chester County, PA (Photo by Kelly Colgan Azar on Flickr, Creative Commons license)

American goldfinch numbers are holding steady in the commonwealth, as they nested in 96% of the atlasing blocks with the highest numbers in suburban and rural developments, places that have both wild and garden foods as well as year around, amply stocked birdfeeders. In addition to weedy fields and suburban gardens, goldfinches also like river flood plains, early second growth forest, and orchards for nesting and food.

It is encouraging to learn that one of North America’s most attractive and appealing birds—“panoplied in jet and gold” as ornithologist Edward Howe Forbush once wrote, has benefited rather than suffered from humanity’s actions.

So, the next time your neighbors complain about the dandelions in your lawn or weeds in your garden, tell them you are growing food for American goldfinches.

 

Migrating Palm Warblers

It’s the middle of October and every day songbird migrants dwindle. Still, between rainstorms one morning the trees fill with warblers, especially yellow-rumps, which haven’t all that far to go. But I spot the pumping tail of a palm warbler too.

A yellow palm warbler in fall plumage

A yellow palm warbler in fall plumage, taken on October 15, 2013, in Chester County (Image by Kelly Colgan Azar on Flickr, Creative Commons license)

The following day three palm warblers sit and bob their tails in the one American elm beside our driveway. The day after that, our First Field plants shake with sparrows—song, field, chipping and at least two white-crowned sparrows.

In the midst of brown sparrow bodies, I pish in a yellow palm warbler, its yellow breast and belly making it the yellow palm warbler subspecies Setophaga palmarum hypochrysea, which nests in coniferous boreal forests east of Ottawa, Canada, and winters mostly along the Gulf Coast. The western palm warbler, S. p. palmarum, nests west of Ottawa and winters primarily along the southeastern coast of the United States and in the West Indies.

Their wintering grounds may account for their common name, but this is a species that nests on the ground or in short shrubs or trees in a black spruce bog environment from Newfoundland and southern Labrador to northeastern British Columbia in Canada, although occasional nests have been reported from northeastern Minnesota across to the northern New England states.

Still, according to the Boreal Songbird Initiative that is “committed to protecting the Canadian Boreal Forest—the largest intact forest on Earth—on behalf of the billions of migrating birds that rely on it,” according to their website, an estimated 98% of palm warblers breed in Canada’s boreal forest. This is the highest number of any warbler species and is followed by Tennessee warblers (97%), Connecticut warblers (91%), blackpoll warblers (82%) and Cape May warblers (83%).

Both subspecies of palm warblers have chestnut caps, giving them the nickname “redpoll warblers” and pump their tails more than any other warbler species so they are also called “tip-up” or “wag-tail” warblers. They also have yellow beneath their tails, but many have subdued colors in fall so it isn’t always possible for the casual observer to separate the subspecies.

A western palm warbler in fall plumage

A western palm warbler in fall plumage, taken on October 6, 2013, in Pymatuning State Park (Image by David Inman on Flickr, Creative Commons license)

However, the western subspecies has a whitish throat and belly and a grayish brown back and wings in contrast with the yellow throat and belly and yellow-green back and wings of the yellow subspecies.

Mostly the western palm warbler migrates west of the Appalachians in the spring, beginning later than the yellow palm warbler and southeastward to the Atlantic coast in the fall earlier than the yellow palm warbler, while the yellow palm warbler migrates earlier northeast along the Appalachian Mountains in spring and follows the Appalachians south later in fall.

In Pennsylvania it is possible to see either subspecies. According to bird banding records from the Powdermill Nature Reserve in western Pennsylvania from 1961 to 2000, westerns outnumbered yellow significantly during migration, but especially in autumn when their nets recorded 1,265 westerns versus 35 yellows. In spring they netted 24 westerns and 13 yellows.

W. Herbert Wilson, Jr., author of the definitive palm warbler account in Birds of North America, hypothesizes that “the earlier spring migration of yellows may reflect a more advanced phenology [blooming of plants] along their typical migration route, the Coastal Plain, compared to western, inland routes of western palm warblers…[and] maybe an earlier breeding season.”

During migration in southeastern Pennsylvania, for example, palm warblers feed on the ground in early spring but switch to feeding in trees as soon as they bud and flower and attract the insects palm warblers prefer.

A yellow palm warbler in spring plumage with a caterpillar in its bill

A yellow palm warbler in spring plumage with a caterpillar in its bill (Image by Kelly Colgan Azar on Flickr, Creative Commons license)

Recent studies in 2013 by Frank LaSorte, a research associate at the Cornell Lab of Ornithology, and colleagues, discovered that many small, insectivorous North American bird species fly looping, clockwise migration routes. Those eastern species use strong southerly tailwinds in spring over the Gulf of Mexico and less severe headwinds in the fall. But they also seem to be following the flush of green vegetation in the spring in search of insects, which may help to explain the difference in migration rates between western and yellow palm warbler species.

Even though scientists have been studying bird migration for many decades and have found so far that they orient using magnetic fields, stars that rotate around the North Star, patterns of polarized light near sunset, as well as learning their route through experience, they are not certain if the birds can easily switch from one navigation process to another during a night when, for instance, it is overcast.

Palm warblers are, like many songbirds, night time migrants. In spring they travel with other early migrants—ruby-crowned kinglets, hermit thrushes, and their closest relative—yellow-rumped warblers. On migration either way they also mingle with other early migrants—pine warblers, chipping sparrows, and eastern bluebirds.

In the fall, they are among the last warblers, along with yellow-rumps, to migrate through Pennsylvania. Then they are usually seen in or near the ground in woodland edges, thickets, brushy areas or on the grassy sand dunes in Presque Isle State Park, according to The Birds of Pennsylvania.

Palm warblers don’t sing much on migration or even on their nesting ground, uttering five buzzy notes per second and reminding one observer of a debilitated chipping sparrow.

Even though much has been learned about migrating palm warblers, only one observer, D. A. Welsh, back in 1971, has studied palm warblers (in a Nova Scotia spruce bog) over their entire breeding period, although earlier observers in Maine, southern Quebec, and New Brunswick described nests they found.

Nest of a Yellow Palm Warbler in Maine

Nest of a Yellow Palm Warbler in Maine, from Ora Knight, Birds of Maine, 1908 (In the public domain)

Maine ornithologist, Ora Willis Knight, in 1904, discovered a yellow palm warbler nesting in a bog consisting “of large open expanses thickly carpeted with sphagnum mosses and dotted with numerous small trees and shrubs” including black spruce, tamarack, Labrador tea, swamp laurel and sedges.

Knight wrote that it is difficult to find nests because the incubating bird won’t flush until you practically step on it and he was not willing to do the alternative—“visit the bog and spend day after day during the nesting season, fighting the voracious mosquitoes.” I know about those mosquitoes. We lived in rural Maine from 1966 until 1971, and even though we were raised in New Jersey, we could not believe the clouds of mosquitoes in our woods.

Apparently, D.A. Welsh was made of sterner stuff. He reported that the average territory in Nova Scotia was between 2.61 and 6.61 acres and included trees around the margin of a bog.

Males established territory around the ten nests he studied by singing from high song posts and chasing interlopers, including American redstarts, dark-eyed juncos, magnolia warblers and common yellowthroats in addition to other palm warblers.

Nest-building occurred between May 26 and June 7 and was constructed in the sphagnum of a peat bog at the base of a small conifer. Even Welsh, though, never saw nest building and so it isn’t known which sex chooses the nest site, if the male assists the female in constructing the nest, what time of day it is built or how long it takes.

He and other researchers discovered that the nest is cup-shaped and hidden well in sphagnum and includes weed stalks, grass and sedges, and woody stems of Labrador tea. It is often lined with feathers including those of spruce and ruffed grouse, American bitterns, barred owls, blue jays, and American robins.

Females brood four to five eggs 11 days and are fed by the males. Both parents feed the nestlings for the 12 days they are in the nest, but Welsh found that the females did most of the feeding, with the males watching closely while the females fed and vice versa. Possible nest predators were gray jays, short-tailed weasels, and garter snakes.

Western palm warbler juvenile

Western palm warbler juvenile (Image by Jeff Bryant on Flickr, Creative Commons license)

Once the young fledged, they stayed with their parents at least eight additional days. Presumably, after those eight days, the young are on their own, but no researcher has verified this.

From 1966 to 1994, Breeding Bird Surveys reported increasing numbers of palm warblers. Christmas Bird Counts from 1995 to 2010 found a modest increase in Florida’s wintering palm warblers. However, at Manomet Banding Station in eastern Massachusetts, they recorded a 76% decline in western palm warblers from 1970 to 2001 and a 26% increase in yellow palm warblers during the spring.

While migrating, palm warblers are often killed in collisions with tall, lighted structures. Increased mining in peatland also may impact palm warblers because they need undisturbed vegetation for nesting, and once disturbed by mining, the peat takes many decades for even a partial recovery.

Still, unlike many songbird migrants, palm warblers are not threatened or endangered. As long as their nesting and wintering ground remain reasonably secure, and they can find plenty of food wherever they travel and live, we can look forward to seeing these birds during migration.