Think Nesting Season is Over?
Not For the American Goldfinch
Spotting an acrobatic flash of yellow flitting around your gardens feeding on flowering seed heads or foraging at your bird feeders is common in many North American yards in the summer. Very likely you’ve seen a male American Goldfinch, with its distinctive black cap and his sweetcorn-yellow summer plumage.
Unlike some other birds, goldfinches are vegetarian, and more specifically, granivores (seed eaters). Most North American songbirds will feed their offspring insects during nesting season, but not the American Goldfinch. Due to this unique adaptation, they establish nests later in the nesting season, usually late June or early July in the East, when seed-heads are abundant enough to support their nestlings.
These birds nest in seed-rich habitat such as shrubby fields, open flood plains, or forest edges. In urban areas they frequent city parks and backyards that provide ideal habitat. See if you can spot their open-cup nests which are approximately three inches across and three to four inches tall. The nest is tightly woven, sometimes sturdy enough to hold water, with the fibers of their favorite seed-producing plants used in the weaving pattern or as a soft lining. Thistles and milkweed have a dual purpose as both a food source and a nesting material.
The American Goldfinch’s late nesting season and exclusive seed diet protects their young from brood parasites such as the Brown-headed Cowbird (Molothrus ater), which lays its eggs in the nests of other birds. The vegetarian diet is insufficient to properly nourish the voracious appetite of these brood parasites, and they quickly perish, leaving the nest to the original inhabitants. If timed well, and food sources are abundant, females will often leave the first nest to find another mate and lay a second clutch. If successful, chicks from the second nest may fledge in September.
American Goldfinches are a true national treasure. Their unique adaptations make them an object of fascination and admiration to backyard gardeners and ornithologists alike. Their vegetarian diets are another reminder of the importance of planting and maintaining native species of flowering plants so we can continue to provide ideal habitat for these late-season nesters. This summer and fall, collect those thistle, sunflower, goldenrod, teasel, and milkweed seeds and establish another healthy patch in your backyard to support next year’s yellow wonders.
To Learn More About the American Goldfinch:
Birds of North America, Online
All About Birds