Nesting Behaviors of the American Goldfinch

Despite its unassuming size, the American goldfinch is unique.

In the summer months, these small songbirds acrobatically dart through meadows in flashes of black and yellow, gathering an array of nesting materials.  

These nesting materials – most notably the down from milkweed – are used to construct a watertight nest. The only known waterproof nest known to ornithologists. 

But the uniqueness doesn’t stop there. 

The American goldfinch is one of the only known bird species to exclusively use its feet to feed their chicks. 

Read on to discover more about the nesting behaviors of the American goldfinch. 

What are American Goldfinches?

As with all my articles, we don’t just jump straight into the action. 

We take our time.

We need to first know what this goldfinch is like. Where does it live? What does it eat?

The American goldfinch is a small, sparrow-sized songbird belonging to the passerine family. It can be found across much of North America – from Alberta, Canada, to Southern US states. 

During the summer months, breeding males sport a striking yellow body with a distinguishable black cap. Their black wings and tail feathers are streaked with white plumage. 

To have the best chance at spotting this finch, head to meadows and weedy fields, where they congregate in small groups to feed on the abundance of seeds. 

Courtship Displays of the American Goldfinch 

Brief description, tick. 

Next up, courtship. 

Before nesting can take place, a male goldfinch has to snatch the attention of the female. 

To do this, he will court her through a series of flight displays and perky songs. 

The healthier the male, the brighter his yellow plumage will be. This signals to the female that he would be an excellent partner in raising her chicks.

Once a female accepts a mate, the pair will fly in wide circles, with the male warbling and the female flying in a zigzag manner. 

After, a territory is established by the male where the female can start constructing the nest. 

Nest Construction of the American Goldfinch 

Female American goldfinches almost always exclusively construct the nests. 

A male may help bring materials for the female to use, but he will play no role in the construction. She has very high standards, and everything has to be perfect.

The nest of an American goldfinch consists of various layers. 

The outer layer, or shell, is formed by weaving together the fibers from dead trees, weeds, vines, catkins as well as grasses.

The rim of the nest is secured using bark, glued together via the sticky and strong silk of spiders and caterpillars. 

The inner nest, where the eggs are laid, is lined with the soft down of plants such as thistles, milkweed and cattails. 

To look at, the nest of the American goldfinch resembles a larger version of a cup nest made by a hummingbird. They’re approximately 3 inches in width. 

But what makes the nests so unique is their incredible waterproofing properties. The females ensure the plant fibers are woven so securely, it creates a watertight space. So much so, the nests are liable to flooding in times of heavy rainfall, and the chicks may perish. 

To date, the nest of the American goldfinch is the only known bird nest that has been found to retain water. 

Nesting Behaviors of the American Goldfinch 

Mating and nest construction begins at the end of summer, peaking in late August – a time when most other bird species have already raised multiple broods and have started their migration. 

Their breeding window is short, and most American goldfinches only produce one clutch of eggs per season. 

But why does the American goldfinch mate so late in the season?

Well, scientists speculate there are two main reasons:

1. Resource Availability 

The first hypothesis is resource availability – both in terms of nesting materials and food. 

Nesting in late summer coincides with the abundance of seed heads from the post-flowering of plants such as milk thistle and milkweed, which can be used as the soft down for nesting substrate. 

The timing also aligns with the abundance of their primary food source, seeds, during the late summer months. Although thistles are preferred, the goldfinch will consume a wide variety of seeds from weeds, flowers, trees, and grasses, along with buds, sap, and berries.

The American goldfinch has several adaptations for its seed-eating diet, including a strong, conical bill that efficiently gathers and splits seeds, and feet with high dexterity, enabling them to climb plant stems and hang from seed heads while feeding, opening a new niche inaccessible to other bird species. 

2. Molting 

The American Goldfinch is unique among certain finch species. 

Unlike most finches, which experience a change in appearance as their feathers wear down over time, the American Goldfinch undergoes a prolonged molting process to obtain their breeding plumage. 

Scientists believe this extended molt, uncommon for temperate zone birds, may be necessary for a bird that relies on a protein-poor seed diet to meet the energy demands of breeding. 

Therefore, while the greater abundance of seeds in late summer compared to May or June provides more food for the young, it is, arguably, the completion of the molt, rather than food availability, that likely dictates the timing of the American Goldfinch’s breeding season.

American Goldfinch Chicks 

Like all songbirds, the chicks of an American goldfinch are born blind and helpless. In the vastly complicated world of scientific terminology, this is referred to as altricial. 

Altricial young require significant parental help, and the goldfinch parents work tirelessly for the next couple of weeks, ensuring enough food is brought from the surrounding meadows to allow the chick to develop in time for the encroaching winter. 

At first, it is predominantly the female that feeds the young. As she hangs on various shrubs, she extracts seeds using her feet. She will eat these seeds, later regurgitating them back to her young. 

Regurgitation is common in birds, however, very few birds are fed exclusively seeds from such an early life. Even species that lead a vegetarian lifestyle as adults still typically start off life on insects, as insects provide more protein that is crucial for growth and development. 

After a few days, the male begins to feed the chicks. A little after two weeks, the fledgling goldfinches depart the nest for good.

Parasite-proof Nesting 

In the natural world, parasites are a real problem. 

Parasites are organisms that depend on a host to survive and spread. They can cause harm, often death, to the host.

But why am I talking about parasitism in the nesting behaviors of goldfinches?

Aren’t parasites small and nasty? The stuff of nightmares? Fleas, tapeworms and the likes?

I mean, sure, you get the standard endo and ectoparasites. But in the world of bird nesting, there’s a whole other world of parasitism: brood-parasitism. 

Brood parasites are often birds that lay their eggs in the nests of other bird species. This behavior spares the parasite the energetically costly process of rearing young, yet ensuring their offspring are well cared for. 

Now, this is where the American goldfinch comes in. 

The Brown-headed Cowbird, native to North America, is a brood parasite. The female specializes in laying her eggs in the nests of other passerine species. Typically, the cowbird is larger than many of their songbird hosts, and their offspring grow quickly, deriving resources away from the host’s own offspring.

Essentially, cowbirds thrive. 

However, the American Goldfinch is adapted for this eventuality. 

Unlike other songbirds, that often resort to an insectivorous diet when raising chicks, the American goldfinch is a strict granivore, or seed-eater. 

Whilst the goldfinch offspring seemingly gain enough protein from seeds alone, this niche diet cannot support the development of the young cowbird. As such, cowbirds that hatch in the nest of an American goldfinch often do not survive. 

Final Thoughts 

So there we have it. Who would have thought that this small, common finch has so many unique nesting characteristics?

Their late mating and nesting, unusual for birds, ensures an abundance of resource availability, not only for building nests, but also to allow their chicks to feed and develop in a relatively short time frame. 

Their highly dexterous legs and feet allow the finch to extract otherwise hard to reach seeds in which they feed their young. 

The nest itself is also unique. So intricately designed, it is the only known bird nest to be watertight.