Post by Jen Berlinghof
The winter landscape, stripped of its lush layers of leaves and fields of flowers, reveals hidden homes. This season of stillness offers a glimpse into animal lives that were carried on clandestinely throughout spring, summer and fall around the Lake County Forest Preserves in northern Illinois. It’s surprising to see how many critters have been busy raising families right under our noses, or sometimes, right above our heads, without us always noticing.
For months in 2021, I walked from the parking lot at Ryerson Conservation Area in Riverwoods to the Welcome Center, past the bioswales—trenches filled with native plants that help manage rainwater runoff, slowing the water down and filtering pollutants—and I never had an inkling of the bustling hive hanging in the hackberry (Celtis occidentalis) tree along the way.
Only after the golden leaves turned a weather-beaten brown and dropped in crunchy piles did I spy the architectural mastery of the bald-faced hornet (Dolichovespula maculata). These basketball-sized nests are constructed in spring with paper-like material made from chewed wood fibers mixed with the hornets’ saliva. Bald-faced hornets build the inner nest with layers of paper cells that look like a honeybee’s comb, each chamber housing an individual egg. Those layers are then encased with a thick outer shell. An opening at the bottom of the nest allows hornets to come and go easily.
While a nest such as this can house about 400 hornets during spring and summer, it’s abandoned come fall and often destroyed by birds that feast on developing larvae inside. The fertilized queen is the only surviving member of the colony, and she will overwinter tucked into a nearby stump or rotten log for protection. She’ll emerge in spring to lay her eggs and start building a new nest. The queen won’t use the nest from prior years, so I will not unwittingly walk beneath a buzzing hive every day come next summer.
Undiscovered bird nests concealed in the shrubbery are a common sight in winter, as well. One kind I’ve come across regularly on recent frosty treks are the dainty, snowflake-crusted cup nests of the American goldfinch (Spinus tristis). Females exclusively build their three-inch abodes at the junctions of vertical branches of small shrubs within open fields of sunflowers, asters and thistles. Hidden from view by clusters of leaves in the verdant months, the finches’ tightly woven, watertight nests are lashed to branches with strong spider silk and lined with downy seed fluff.
These bright, sunny-yellow birds of summer actually stick around in winter, sporting subdued colors that make them so much less conspicuous that many people think finches migrate south for the winter. During their fall feather molt, American goldfinches grow a new set of duller feathers much denser than their summer plumage, providing an additional layer of insulation to help keep them warm. Though they abandon their nests after breeding, these feisty birds have been known to burrow under the snow to form a cozy sleeping cavity to stay warm on a cold winter’s night. Keep watch for finches at your bird feeders all winter long.
When I look higher, towards the tips of the towering oak trees, I discover another animal nest that is not necessarily abandoned in winter. What appears to be a big clump of leaves with a few errant sticks protruding is in fact an eastern gray squirrel (Sciurus carolinensis) nest, or drey. While squirrels will gladly take over an old woodpecker hole as shelter, they also build these leafy dreys as both summer and winter homes. Twigs, often gnawed from a tree when the leaves are still intact, form the framework upon which layers of more leaves are stacked, woven and stuffed.
The summer drey is flatter, lighter and more open, keeping it airy in the warm months. Some squirrel nests you see in winter may look a bit haphazard and falling apart, which could be a summer nest—or it could be an imposter altogether. Squirrels often build phony nests as a way of tricking predators and diverting attention away from their real homes. Winter dreys appear far sturdier. The thick walls of overlapping natural materials keep wind, water and snow from penetrating the interior, while pockets of air provide insulation that keep cold out and heat in.
Squirrels rely heavily on these homes in winter to stave off freezing temperatures, especially when the thermometer plunges at night. Sometimes two or more squirrels cozy up together, their collective body heat warming the nest interior to temperatures far beyond that of the outside. Research has shown the inside of an occupied drey can be an astonishing 60 to 85 degrees Fahrenheit warmer than the ambient temperature, creating a one-of-a-kind squirrel sauna.
I like to think of these nests that are revealed in winter as little gems of nature, sparking curiosity about the lives of animals in Lake County and beyond. And as we celebrate the 10-year milestone (!) of the Lake County Nature blog this January, I’m hopeful that through the years, it too has uncovered nuggets of nature that ignite wonder for our readers, and that it’s provided inspiration to explore the natural world in a deep and meaningful way.