Faville Grove’s prairies are full of composites in bloom! Madison Audubon photo
With the twilight of summer come the composites. Goldenrods, asters, sunflowers—all the same family, Compositae, with the composite result being a hue of yellows across the landscape. Prairie dock, cup plant, bidens, sawtooth sunflower, and showy goldenrod paint a prairie in a worn hue of yellow suggesting the dog days of summer. At the same time, sky blue aster, smooth blue aster, and the gentians offer a quick alert: cool weather is coming and the warmth of summer wanes.
No bird is a pastiche of the late summer prairie better than the American goldfinch. With its yellow body, the bird could hide among the goldenrod, except for the male’s black wing bars and orange bill and legs.
American goldfinch photo by Mick Thompson
It’s well documented that the goldfinch is one of the latest nesting songbirds in Wisconsin. In fact, it’s likely that you could find a handful of nests by simply walking through a prairie restoration at Faville Grove Sanctuary this week. Many goldfinches start building nests in the middle of July, using thistle down and other material like cattail fluff, well after most songbirds have finished nesting for the year. Incredibly, many goldfinches will also produce a second brood, nesting well into September, with fledgling individuals being spotted as late as the middle of October.
American goldfinch nesting in late summer at Faville Grove. Photo by David Musolf
While these tardy goldfinches squeeze in another brood, it comes at a cost. During the high summer, in mid-July, goldfinches are afforded the time to romanticize, to revel in song and flight, and to construct an intricate nest of woven silk from thistle and milkweed and willow. During mid-July, the average time to build the nest is 13 days. By late August, the pace has quickened, and a nest is built in an average of 5.6 days. This hastened pace is likely because the pair has already reproduced and is convinced that the other is a good partner, but also because the frosts are coming, seed is ripening and flying with the wind, and winter is coming.
Goldfinches are strict vegetarians, subsisting almost entirely on a diet of seed. Their favored seed source is from the Compositae, and Faville Grove Sanctuary is rich with asters, goldenrods, and sunflowers. In short, a prairie restoration here makes a fat goldfinch.
But body mass is not the only diet-related effect for goldfinches. Carotenoids obtained through the diet play a key part in the vibrancy of their plumage. The health of the bird, shaped through its diet, signals to the female whether he might make a good mate. Goldfinches deprived of carotenoids in lab studies show duller plumage and declining health.
While the asters shape the diet of the goldfinch, they may also shape the distribution of nesting territory. A study by Allen Stokes on Wingra Marsh in Madison found that as goldfinches nested in higher and higher densities, nest placement in an aster species became less likely. In years of low abundance, a goldfinch might nest in a sawtooth sunflower, raising its young next to a buffet of sunflower seeds. But in high abundance years, Stokes theorized that the competition was too great and goldfinches could not defend their territories sufficiently to nest in these “prime” spots.
I believe we may see this sort of behavior at Faville Grove Sanctuary. Areas with monotypes of cup plant or sawtooth sunflower tend to have tremendous flocks of goldfinches—it’s a communal feeding area where no birds are nesting. But overall, our prairie restorations provide huge amounts of food for the goldfinches, so much so that seed collectors are in competition with the birds when harvesting old field thistle and prairie dock. Really a fake competition, as there’s plenty of both to go around.
One final intricacy of this late nesting and seed-crazed diet is that goldfinches avoid nest parasitism by brown-headed cowbirds. Cowbirds don’t typically lay eggs this late, so records of parasitism are rare, and cowbird hatchlings need a diet of insects in order to grow; they die within days of subsisting on the goldfinch diet.
A feasting goldfinch, photo by Kelly Colgan Azar
You can find goldfinches anywhere within Faville Grove Sanctuary, and you’ll notice their economy built around seed, their sinuous flight, and their brilliant plumage, coalescing now as the sun sets on summer and the sawtooth sunflower brightly decorates a late August dusk.
Written by Drew Harry, Faville Grove Sanctuary land steward
