American Goldfinch: Common bird with uncommon habits

 

Illustration by Adelaide Tyrol

By Barbara Mackay

I love the fact that there is always something new to observe in nature. Take goldfinches, for example. I have often watched them devour milkweed seeds from an acrobatic, upside-down position. Recently, I spotted several bright yellow males perched atop dandelion stems, plucking the seedheads at a frenzied pace. Previously, I had only seen them snag dandelions in mid-air.

Of all our native songbirds, American goldfinches (Spinus tristis) are perhaps the most consistent vegetarians. Thistles are a favorite food source and nest material. Sunflower seeds are another top meal choice, something you have probably observed if you offer these popular seeds in a feeder. Aside from our freebies, goldfinches also eat seeds from grasses, weeds, teasel, mullein, and ragweed, along with birch and alder buds, maple sap, and berries. An uncommon agility allows them to extract seeds from any position. Their short, pointed, conical bills are well-suited to crack open hulls and other tough packaging.

Goldfinches feed their newborn broods a strict diet of regurgitated seeds rather than the high-protein insects favored by other passerine (perching) birds. Interestingly, this diet gives goldfinch babies a means of defense against a threatening parasite, the cowbird. Cowbirds are known for depositing their eggs in other birds’ nests, where the large cowbird nestling often receives an unfair share of food from the unsuspecting parent, leaving other chicks at risk for starvation. But baby cowbirds can’t survive off seeds, and a cowbird hatchling in a goldfinch nest is doomed.

Goldfinches’ vegetarianism also influences nesting time.  Although goldfinches pair up in the spring like other migrating songbirds, they don’t get down to the business of raising young right away. Instead, they tend to wait until thistles, milkweeds, and other wildflowers start going to seed in summer to breed and nest. At this time each male selects his own territory, flying in circles around an open area dense with weeds and shrubs, preferably near a water source (even a reliable roadside ditch will do). Warbling from a high perch, he defends his area by chasing other males away. His mate selects a suitable site for a nest and constructs it over four to six days while he helps by gathering material.

A goldfinch nest can be hard to find amid summer foliage, but it’s easy to identify. Look for a sturdy, cup-shaped nest built into the fork of a branch in a sapling or large bush. Small twigs, bark strips, and long plant fibers form the outside, which measures close to three inches across. Spider web silk acts as a glue to hold it together. The inside cup is deep, smooth, round, and firm. It is lined with catkins, bits of wool, and so much thistle and milkweed or cattail down that the pale, bluish-white eggs are almost hidden. Eventually the down becomes compacted during incubation and as the hatched chicks shift around. The nest is so tightly woven that it can fill up in a deluge of rain, sometimes drowning its inhabitants.

One clue to identifying a goldfinch nest is its characteristic squalor. Unlike other birds, goldfinches stop removing fecal sacs after the babies become active, about a week after hatching. Instinctively perhaps, the chicks begin to defecate along the edge of the nest. The nestling period lasts from 11-17 days, and there are usually five chicks, so you can imagine the buildup of dried waste. Hygiene aside, the durable nest maintains its shape well, still looking re-usable in midwinter. The thistle down gives it a cozy, cottony appearance.

Goldfinches, like most songbirds, completely replace their feathers once a year, commonly before fall migration. The summer feathers are gradually pushed out by a more subdued winter plumage. The following spring, a partial molt results in the attractive colors that enhance courtship. Male goldfinches become canary yellow with a black cap and black wings, each marked with a white wing bar. Females become a soft yellowish green with yellow belly feathers. Both sexes’ bills, legs, and feet change from dark brown to a soft pink-orange-yellow color.

Unlike most birds, goldfinches do not continue to defend a territory once a family is started, and members of a flock move freely in and out of each other’s areas. They are social birds, flocking together in winter and amicably sharing bird feeders at any time. This time of year, see if you can spot one gathering seeds and fluff in the milkweed patch.

Barbara Mackay is a teacher and naturalist who lives in northern Vermont. The Outside Story is assigned and edited by Northern Woodlands magazine.

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