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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.

 

2 thoughts on “Thistle-Birds

  1. Thanks for featuring the AMGF. I have always wondered why they sing so much way ahead of nesting and breeding. In Michigan the thistle is just now luxurious. I do see fewer females now so I assume they have more duties elsewhere. I always learn from your writings.

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