Sandhill cranes that breed in the upper Midwest and central Canada begin gathering in Indiana near the end of September, and their numbers grow until mid- to late November, when they peak at about 20,000. Imagine 20,000 of these majestic birds together in the same place less than half a day’s drive from Champaign-Urbana.

Ready or not October is here, and it's a month full of dramatic change in the natural world. This week's commentary takes stock of what's coming (and what's going).