Here come the cranes. In short order, Wisconsin will be swamped with cranes, and those cranes will stake an early claim to swamps. Forging through the ice, these sandhills fly as they have for millennia.
The sandhills stream like a river up the continent, awakening from Florida, which claims its own sandhill habitat—sandhill scrub and woodland, literally hills of sand, some of them ancient dunes that formed islands on the interior of Florida thousands of years ago, now rich with an endemic flora that evolved on those isolated dune strands and their own endemic bird species, the Florida scrub jay. But this is beside the point for our sandhills, for they are named for the sandhills of Nebraska, where they migrate in massive numbers along the Platte River.
Why, though, does Nebraska have hills made of sand? Again, we circle back to dunes. Pleistocene-era glaciers ground down the Rocky Mountains and washed sediment onto the Great Plains 1.8 million to 10,000 years ago. During dry spells, the Rocky Mountain sand that had washed into Nebraska could not grow any vegetation, and thus shifting sand dunes formed.
Aerial view of Nebraska’s sandhills region today
Today, prairie grasses and forbs mostly hold the soil of Nebraska’s sandhills, and those sandhill cranes migrate through feasting on emergent vegetation and invertebrates found in the numerous lakes and wetlands. Because of the poor soils for agriculture, this region remains one of the largest prairie expanses in North America—and is the largest dune field in North America. After glaciation, perhaps those wind-blown Nebraska sands rained down phosphorous on the sterile glacier-exfoliated soils of Wisconsin—much like the Sahara Desert subsidizes phosphorus in the Amazon Rainforest today. But this is beside the point for our sandhill cranes, who pre-date even the start of those Pleistocene glaciations; crane fossils date back 2.5 million years. The sandhill crane has seen the advance of mountains of ice, the shifting of thousands of square miles of sand, and the grinding of mountain ranges.
In “Marshland Elegy,” Aldo Leopold said of crane marshes: “a sense of time lies thick and heavy in such a place. The peat layers that comprise the bog are laid down in the basin of an ancient lake. The cranes stand, as it were, upon the sodden pages of their own history.” Leopold was writing on the demise and eventual extinction of the sandhill crane, but thanks to conservation efforts, the bird’s population remains strong today. Even on the seemingly flat ground of Leopold’s sand county (Adams), a look (with LiDAR) to the sandy uplands where he stood reveals, what else, sand dunes.
Recent research suggests these dunes in central Wisconsin formed over 10,000 years ago. Wisconsin’s central sands host plentiful sandhill cranes today, Though the sand is not exactly their desire; rather, they enjoy the abundant wetlands, the soggy ground, the marshlands, swamplands, bogs, fens, ponds, and shores. The presence of sand and sand dunes really has nothing to do with their breeding cycle. It is entirely beside the point.
From the ancient glacial Lake Wisconsin, at say Necedah, we can look west to Wisconsin’s driftless and see that during the breeding season cranes occupy a smaller portion of the area. They do occur on river and valley bottoms throughout the driftless region, but not as numerous as in the eastern part of the state. Researchers in southern Wisconsin found the highest nesting density of sandhill cranes on bogs and floating mats—areas of stagnant water, low flow-through, and low mineral inputs. These mats provide safety from predators, and indeed at Faville Grove they seem to rank among the favorite locations for sandhill crane nesting. But where are the sand dunes in southeastern Wisconsin for the sandhill cranes? That is beside the point.
This map of relative abundance of sandhill cranes during the breeding season shows the importance of Wisconsin, especially eastern Wisconsin, for this species. Two summers ago, we had a group, mostly from Illinois, take a tour of the sanctuary. Stopping at a crane nest, the field trip attendees were in awe of the majesty of the cranes. We certainly appreciated the cranes, and enjoyed watching the developments on their nest, but their nesting did not seem that extraordinary. But then, Illinois does not have quite the population of cranes that Wisconsin does, and those cranes seem to know something that we don’t. How can a crane arrive on the Illinois-Wisconsin border, look north, and say “this is the point.”
This is a rendering of the Laurentide ice sheet, that block of ice we referred to earlier. It left Wisconsin about 12,000 years ago, and since then, it seems that cranes have prospered amid that melting ice. Look again at the breeding map today—it sketches the rough outlines of that ice sheet. Do cranes know about Pleistocene Ice, or are they more partial to snowball earth?
Finally, we are getting to the point, and for a sandhill crane arriving in Wisconsin today, the point is not sand but wetland. Those glaciers scoured the earth and made level ground with slight undulations where abundant wetlands form. Driving back to Faville Grove from Necedah you’ll pass extensive wetlands at Pine Island; you’ll cross the Wisconsin River and its bottomlands and head south past Goose Pond and the prairie potholes of the former Arlington Prairie; you’ll fly by Cherokee Marsh and Token Creek; and once you’ve hit I-94 you’ll encounter linear wetlands formed in between drumlins, series after series most prominent at Goose Lake, which retains its boggy tamarack wetlands. And finally at Favile Grove, from a point on the Overlook Prairie scanning Faville Marsh, you’ll see the sandhill crane, perhaps linked to sand for every part of its journey, but here linked to areas not quite water and not quite land—those magical wetlands.
Written by Drew Harry, Faville Grove Sanctuary land steward
Cover photo by Mick Thompson
