Lake Renwick 



Unlikely Haven for the Endangered 



by Jerry Sullivan 



ONE OF THE FINEST natural areas in north- 

 eastern Illinois is a played out, water-filled 

 gravel pit. Carved by a scouring dragline 

 through 50 years of digging in the glacial 

 outwash just east of the town of Plainfield, it once sup- 

 plied raw materials for concrete and ballast for every- 

 thing from county roads to the building of the Joliet, 

 Plainfield, and Aurora Railroad. 



At various times in its history, Lake Renwick, to 

 give the pit its proper name, has also been a beach resort 

 and the site of a dance hall. It remains a sort of sur- 

 reptitious fishing hole, a place for local kids to sneak 

 into, as their fathers did before them, in hopes of hook- 

 ing a carp or a large-mouth bass before the gravel com- 

 pany guard sees them. 



U.S. Route 30 skirts the southern shore; the Elgin, 

 Joliet & Eastern tracks mark the northern boundary. 

 Until three years ago, the noisy rattle of the gravel 

 washer was a routine sound of summer. 



But on three tiny islands in the middle of this 

 accidental lake, one of Illinois' largest and most diverse 

 heron rookeries provides a nesting ground for at least 

 four species of these long-legged birds, two of them rare 

 enough to earn the dubious distinction of a place on 

 Illinois' Endangered Species list. 



The biggest of them is the great blue heron, the 

 largest member of its family in North America, a steel- 

 gray giant with a wing span of six feet. Last year, the 

 three tiny islands supported 73 tree-top nests of great 

 blues. 



Just below them, hidden in the upper branches of 

 the box elders, are 66 nests of the sleek white great egret, 

 one of the endangered species. Below them, down 

 amidst the scrub, are more than 300 nests of the black- 



crowned night heron, the other endangered species rep- 

 resented here. 



And on the ground, an interesting alien, the cattle 

 egret, a moderate-size white bird, a native of the African 

 plains that managed to get to the American Midwest 

 through its own unaided efforts. Cattle egrets were first 

 sighted in Illinois in 1952. They began nesting at Lake 

 Renwick in 1970 or 1971, and last year they occupied 17 

 nests on these crowded little islands. 



The presence of these birds in this unlikely place is 

 both mysterious and easily explained, a product of a 

 combination of accident and inexorable forces, a blend 

 of the patterns and regularities of natural history and the 

 weird contingencies of human history. 



The story of Lake Renwick, like nearly everything 

 else in this part of the world, starts with the glaciers. 

 About 15,000 years ago, the towering ice front of the 

 Wisconsin glacier stood just a few miles to the east of this 

 spot. The ice was melting, wasting away, and huge tor- 

 rents of meltwater, milky with ground rock, were pour- 

 ing west toward the Illinois River valley. The speed and 

 volume of the moving water determines the traces left 

 behind. Gravel drops out at high speeds; sand can be 

 carried by slower water. East of the DuPage River, the 

 deposits, formally part of the Mackinaw Member of the 

 Henry Formation, are well sorted layers of sand and 

 gravel, a clear record of fast and slow water, laid down to 

 await the invention of concrete and railways. 



In the somewhat shorter run, the story starts with 

 minor excavations for road gravel begun by the Town- 

 ship of Plainfield in the late years of the 19th century. 

 From then to now, the general outlines of the history are 

 quite clear, although many of the details change from 

 source to source. 



10 



Jerry Sullivan edited Chicago Area Birds, published recently by 

 Chicago Review Press; writes a column, "Field and Street," for 

 the Chicago Reader; and has written extensively on birds of the 

 Chicago area. 



Double-crested cormorants (viewed in Florida) . A flock of these birds (en- 

 dangered in Illinois) took up residence at Lake Renwick during the spring 

 months of 1985; a pair ofimmatures spent the entire summer there. 



