It all boils down to a lack of disturbance. When the majority of the local railroad tracks were laid down in the late 19th-early 20th century, the landscape was very different from how it is today. The railroad tracks were installed across prairies and through woodlands. Over time, communities sprang up along railroad tracks as the railroad became a primary mode of transportation. Farms replaced the natural landscapes, destroying habitat for so many species of plants and animals. However, a thin strip of land on either side of the railroad tracks was usually left as a buffer. And for a long time, no one paid any mind to what happened in those areas. They were left to grow wild and became the last strongholds for many species. Later on, much of those lush areas were subjected to herbicides in order to clear the way. But not all - some were left alone, and today, many biologists credit those "green corridors" with providing habitat for some critically imperiled species of plants that may not have survived had the railroad tracks not been built.
To this day, the edges of railroad tracks can provide crucial habitat for a number of plants and animals. When the tracks bisect or border a preserve, you're generally going to find a greater diversity of species. The open nature of a ROW provides habitat for species typically associated with savanna or prairie ecosystems, particularly if the ROW is located in or along a wooded preserve. In some cases, tracks were installed while the surrounding area was open, but then over time, circumstances (including suppression of fire) allowed the area to become overgrown and wooded, relegating the open-habitat species to the narrow railroad corridor.
Sometimes, snakes frequent railroad tracks located away from preserves, sometimes very far away from preserves in built-up, highly urban areas. In these areas, the railroad tracks and the exceedingly narrow strip of junk habitat offer the bare minimum of what a few species require to survive. Plains garter snakes (Thamnophis radix) and brown snakes (Storeria dekayi), both small, rugged, live-bearing generalists, are prime examples of such snakes that can withstand truly urban environments. Those two species are the most common snakes in Chicago, and by far the most common snakes I see. And of course, the more cover they have access to, the better chances they have of properly thermoregulating, finding food, and staying concealed from predators.
If you know where to look, you might find other species of snakes along railroad tracks in or just outside of Chicago, such as redbelly snakes (Storeria occipitomaculata) and smooth green snakes (Opheodrys vernalis). On September 13th, I explored a long-abandoned ROW in northern Cook County that was reported to support smooth green snakes. Of course, the reports were from the late 1990s, and a lot can happen in almost twenty years. Turns out that although there are still a few tiny patches of prairie remnant along the ROW, the tracks are now being taken over by all kinds of pioneer species such as teasel, milkweed, thistle, and goldenrod - most of which are invasive. I walked about four miles, two in each direction, and surprisingly, I did not find one snake - not even a brown or garter. Very unusual.
Looking down the tracks.
Sights like this make field herpers salivate. Though I came across a number of these piles of old railroad ties and other trash, I didn't find any snakes.
Between the tracks and this electrical substation lie a thin strip of relatively undisturbed prairie "remnant"; as far as I can tell, based on old aerial maps and plat maps, this area hasn't been touched much.
I swear, I didn't notice these signs until I was on my way out...
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