Natural Events

By Jack MacRae

Here’s what’s debuting on nature’s stage in Chicago Wilderness

Early Fall

Little Droppings

Hummingbird feces require magnification to be truly appreciated. During the fall, a microscopic examination of their droppings reveals a high percentage of insect wings, legs, and antennae. As they prepare for migration, ruby-throated hummingbirds enter into a state of insect hyperphagia; that is, they binge on bugs. After a few days of gorging on flies, these minuscule birds can nearly double their size, fattening themselves from 2.5 grams to 4.5 grams for their flight to the tropics.

Walnuts

Abscission is a favorite word among the spelling bee crowd. It’s a botanical term used to describe the highly complex separation of leaves, flowers, and fruits from their respective plants at the end of a growing season. In a nutshell, our deciduous trees produce hormones to inhibit growth and promote dormancy, resulting in leaves and nuts falling off before winter sets in.

Compared to other trees, abscission in black walnut trees occurs early in the season. Walnuts often drop their leaves during the first cold snap at the end of September. They hang on to their big green nuts a tad longer. Chicago Wilderness is blessed with many grand walnut trees. Examine the twigs and branches for the three-lobed scar where the leaf fell off. It looks like a little monkey face.

Middle Fall

Black Oak Kettle

Exactly 20 Septembers ago, shortly after sunup in the Braidwood Dunes south of Chicago, I watched a stream of broad-winged hawks — at least 50, probably more — take flight from their roost in the black oak savanna. They spiraled up from the trees, easily caught a thermal on that unseasonably hot day, and sailed out of sight. They were most likely on their way to South America, where they’ll eat a lot of reptiles.

Across northern North America, broad-winged hawks migrate in flocks, or kettles, that increase in size throughout their long trip. Small kettles are continually combining to make large kettles. Large kettles combine to make huge kettles. On certain days, in certain locations, a kettle may contain hundreds or thousands of these broad-winged migrants. Experts estimate about 4,000 broad-winged hawks pass through the Chicago Wilderness annually, most on breezy days the week before and after the autumnal equinox. Look for wide tails with alternating dark and light bands of equal width — and, of course, their broad wings.

Sweet Virginia

Virginia creeper is a common — and most certainly not creepy — vine that gives our open woods so much rich color. Also known as woodbine, Virginia creeper is a deep glossy green in summer and an earthy red in the fall. It grows frequently along woodland paths and covers the trunks of many trees to a height of 35 feet.

Late Fall

Bird Brains

Black-capped chickadees don’t get fat for the winter, but they do grow a bigger brain. The hippocampus (the portion of the avian brain used for spatial memory) expands during the autumn, during a time when chickadees are required to memorize the location of the many thousands of seeds they are hiding. Science has shown that chickadees use a complex system of both global landmarks and local cues to recall the location of their seed caches. If a chickadee’s hippocampus is damaged, it will still hide food, but won’t remember where to find it.

Raccoon Autumn

As they approach their first winter, young male raccoons spend a lot of time rummaging for food. It’s important that they get some flab on their bones. A nice layer of fat may be a matter of survival during a rough winter — at times, only the portly survive. The ultimate omnivore, raccoons will eat from all the food groups — including the underappreciated “trash group” — to build a good fat reserve.

The largest raccoon I’ve seen was an urban dweller in an alley behind Clark Street, near Wrigley Field. I watched it waddle from a dumpster used by a wonderful old German restaurant. Granted, it was 3:30 a.m. and I was heading home from an establishment called the Wild Hare, but I swear he was as wide as the Ford Pinto parked nearby.

Something I never knew before: raccoon is a derivation of a native Algonquin word for “the animal that scratches with its hands.”