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All summer, it’s much easier to hear red-eyed vireos singing than to actually see one high in the treetops. This signing male was a lucky find! Photo by Emily Stone.

Cold air filled my lungs as I climbed yet another flight of stairs up to the observation tower at Copper Falls State Park. It was interesting looking out through the twigs and trunks. 

The lack of leaves in this “see-through season” reveals aspects of the landscape otherwise obscured. For example, “Check out that nest!” I exclaimed to my friend, and we admired the small cup suspended between a Y in the sugar maple twigs. It was a lovely reminder of a favorite summer resident, now gone for the winter.

The placement of the nest dangling below the forked twigs, plus the few pale strips of paper from a bald-faced hornet nest woven among grass, bark and pine needles, told me that it was likely built by a red-eyed vireo. 

While red-eyed vireos are one of the most common birds of eastern and central North American, these small, olive-green songbirds are hard to see among the leaves in the dense forests they prefer. Once the leaves fall, though, their nests are suddenly one of the most visible and recognizable of any songbird.

It’s the female vireo who builds the nest in spring. She usually chooses a deciduous tree or shrub and places the nest 10-15 feet above the ground, and far enough out from the trunk so that it doesn’t block their view. 

Suspending a nest near the tips of thin branches reduces access for heavy nest predators like squirrels. 
On the chosen branch, the vireo weaves together fibrous strips of the inner bark of trees and other plant fibers to suspend the nest between the twigs. Pine needles often line the 2-inch-diameter inner cup. Spider webs help stick it all together. 

As mentioned above, vireos often decorate the outside of their masterpiece with paper strips stolen from last season’s abandoned bald-faced hornet nests, even when those nests are not found nearby. Naturalists suspect that décor can trick potential predators into thinking it’s the nest of a furious stinger instead of a tasty songbird. Strips of birch bark often add to the papery look. 

Almost every bird nest is a work of art. They are also feats of engineering that gently cup fragile eggs and chicks while withstanding storms, and then remain intact long past their intended use. Plus, they were constructed without opposable thumbs! 

There’s a display at the Cable Natural History Museum that reinforces my awe. A museum naturalist, decades ago, deconstructed a red-eyed vireo nest and catalogued each component. 

The nest included: 1 cherry stem, 1 piece of paper, 1 ball of tree sap, 2 pieces of thread, 7 fir needles, 9 plant buds, 69 pine needle sheaths, 16 pieces of hornet nest, 24 twigs, 50 animal hairs, 346 pieces of birch bark, 347 pine needles, 427 pieces of inner bark, and 16 pieces of spider web. 

The naturalist arranged these objects, minus the spider webs, in a beautiful display that hangs in our classroom. 

Despite the birds’ hard work, and the hornet paper, red-eyed vireo nests are vulnerable to nest parasitism by brown-headed cowbirds. When vireos can place their nests in the heart of a forest this is less common, but any vireo nest near a forest edge may end up with a cowbird egg among the 3-4 vireo eggs. 

The cowbird hatches first, grows faster and bigger, and will often push their adopted siblings out of the nest. Occasionally vireos will cover up the cowbird eggs and try again, but more often the parents just feed the big baby as one of their own. 

Vireos may nest multiple times per summer, especially if early nests fail. 

Recently I noticed two vireo nests in the tops of trees surrounding my own driveway. Although the nests are much higher than average for a red-eyed vireo, that was the only vireo species I heard singing last summer. 

Warbling vireos are known to nest up high, but I would have recognized their run-on song, which sounds like them saying, as if to a caterpillar, “when I see you, I will squeeze you, and I’ll squeeze you ‘til you squirt!” 

Instead, I heard red-eyed vireos singing the incessant phrases “hear I am, over here, in a tree, look at me, vireo!”

As their abandoned nests fill with white snow instead of white eggs, the vireos themselves are filling up on fruit in the Amazon basin of South America. When they return next spring, the females will start building new nests. Once the leaves fall, we’ll have a whole new set of treasures to discover in “see-through season.” 

Emily Stone is Naturalist/Education Director at the Cable Natural History Museum. Her award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is available to purchase at cablemuseum.org/books and at your local independent bookstore, too. For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is open with our brand-new exhibit: “Anaamaagon: Under the Snow.”