Natural Events

by Jack MacRae

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

Early Spring

Crowded Snakes

Some of the highest densities of snakes recorded in North America have occurred in Chicago. Seventy years ago, more than 500 snakes (mostly eastern garter snakes) lived in four empty lots near the intersection of Odell Avenue and School Street. Biologists Francis, Darwin, and Edward caught hundreds of them in the mid-1940s. The snakes could be seen soaking up the afternoon sun on the southwest slopes of small hills. Eastern garter snakes come out of hibernation as the spring daytime temperatures hit 70 degrees. Some years they’re slithering as early as the Spring Equinox. Edward used to mark eastern garter snakes after they had surfaced to study their movements. They don’t wait to mate; breeding occurs shortly after spring emergence.

Offspring Asynchronicity

Great horned owls hatch asynchronously. This natural strategy of hatching at one- to two-day intervals helps ensure that at least one will survive. The first bird hatched — in this region it’s usually in late February or early March — is the first to eat and get big. Younger siblings must wait. In years when food is scarce, the youngest may not get a meal and will die, leaving scarce rations for the strongest. It doesn’t help that some of the meals are spilled from the nest. I remember a collection of assorted flicker, mallard, and cottontail parts under a tree along Salt Creek in Oak Brook a few years ago. That’s good eating! The doting great horned father brings most of the food, about 300 grams for each offspring. Mom is responsible for keeping the nest warm.

Middle Spring

Rabbit Dancing

When rabbits dance, there is a lot of hipping and hopping. Both boy and girl eastern cottontails take turns bounding, leaping, and twisting, Baryshnikov-like, with the other rabbit dashing underneath its airborne partner. They perform these movements rapidly over and over. It’s not a common sight — I’ve only seen rabbits dance on one occasion. There were several pairs kicking up their heels in a moonlit clearing in the woods. Quite romantic. As with many animals, rabbit dancing is a ritualistic prelude to copulation. In our region, mating can start in February, with the earliest bunnies appearing in March.

Spring Cuties

Spring beauties are pretty little pinkish-white flowers that are common in both oak and maple woods. They bloom early, opening on sunny days in April. They keep closed on cloudy days, and once the tree canopy opens and shades the ground, spring beauties are done blooming for the year. Scientists have learned that the pink striped petals contain ultraviolet markers, unseen by human eyes, which direct insects into the flower’s nectar chamber. And spring beauties are popular with pollinators. I have read there are more than 100 insect species — mostly bees and flies but also a few butterflies — that pay a call. When I told my wife I was writing about spring beauties I told her I was going to include her.

Late Spring

Cormorant’s Eye

The corneas of cormorants have been closely scrutinized by avian ophthalmologists. Eye doctors are examining the seeming ability of these aquatic birds to see clearly through both air and water. Specifically, they’re interested in the structure of the cornea, the clear outer portion of the eye. The function of the stationary cornea is to refract light entering the eye, allowing the lens to then bring objects into focus. As someone who has gazed into the eyes of hundreds of different animals, I can say without hyperbole that the eyes of a double-crested cormorant are some of the prettiest in the animal kingdom. They have an emerald-turquoise iris encircled by 20 evenly spaced aquamarine droplets. In spring breeding plumage, the colors really pop.

Migratory Celebration

In the Spring 2001 edition of this Natural Events Calendar, I wrote about wishing International Migratory Bird Day would be bigger than St. Patrick’s Day. It’s not, of course, but I have noticed an increased buzz! More and more organizations are participating in this happening, which celebrates the return of several million birds of every color, shape, and size to the area. IMBD is actually a very easy and inexpensive event for birdy agencies to put on; the guests of honor are free and dependable. Birds are remarkably consistent with their arrival dates; watch in the middle of May when the warblers really hit our region.