Traveling through a remote part of Cass County in June 2012, I was looking for an access road or pathway to an even more remote natural area, when I noticed a large expanse of bare earth seemingly carved out of the bluff side. I knew by its yellowish-brown color and the near vertical steepness of the cut that this was pure loess.
Loess is a windblown soil that was originally deposited in ancient river valleys during the last Ice Age, over 12,000 years ago; during dry periods, extremely high winds blew the fine dust-like sediments onto the surrounding uplands. The loess accumulated over long periods of time, perhaps only a few feet per 1,000 years. Even so, in parts of Illinois, loess deposits can be greater than 100 feet thick.
What I saw in Cass County was an exposure from such a deposit. Even more interesting, though, were the bank swallows that had burrowed nesting holes into the vertical loess exposure. Loess has special properties that allow it to maintain its shape and stability, even on a vertical cut, which looks like a sheer rock cliff. I remembered this cut and the same bank swallow colony from over 20 years ago; so multiple generations of swallows have fledged from this artificial feature in the landscape. And even though I have not been to the site this year, I know they are there again.
I wrote about a bank swallow colony in my book Side Channels in a chapter called “Wings Over the River”:
“Even though large [bank swallow] colonies have many disadvantages to birds, and they can actually attract the attention of predators, colonies are highly effective at predator detection – and defense in some cases (mobbing the predator). While walking along Salt Creek in Logan County one spring, I noticed a bank swallow colony just below the steep drop off of the creek bank. When I was directly above the burrows, the swallows formed themselves into a great whirling cloud that circled directly overhead, with each bird vociferously calling…A large bank swallow colony is a chaotic affair much like a schoolyard full of highly energetic children during recess on the first warm, sunny spring day.”
It was quite an interesting experience.
The colony in Cass County, south of Bluff Springs, is on private land, but it is easy to see from the roadside, about a half-mile north of the intersection of county roads 400N and 1300E. Binoculars would be a good idea.
[NOTE: An earlier version of this essay appeared in the Pekin Daily Times online in 2012.]