I was pulling into the parking lot on yet another shopping trip today when I noticed a beautiful black cat by the curb. He was looking around and then he disappeared.
I pulled the car around to where he was and parked, to see that there was a storm drain there, and the cat was nowhere in sight. I looked across the road, and saw another storm drain just like it. Not being in a hurry to shop, I waited for while, looking down the storm drain near me and across the road.
After about two minutes, up pops the cat, across the street.
I have long suspected that a lot of wildlife navigates the urban and suburban landscape through storm drains, and I’d like to find if anyone’s done a study of this, anywhere.
The typical model of a road is as a variably hazardous, sterile barrier that different species cross with different success. A road is also an edge, allowing predators and parasites entry into communities that were once continuous with square miles of similar habitat. The only clearings the size of roads before agriculture were from tree falls. A large tree collapsing in a forest can clear a good fraction of an acre on its way down, allowing a different, meadow community to exist briefly before its descendants move on to the next clearing*.
The difference between clearing by tree fall and clearing by transportation network is that the forest surrounds a tree fall, while it is surrounded by road networks.
The communities that remain and develop in those forest fragments between roads are determined by how good each species is at crossing a road. A country road with a car coming by every 10 minutes is much different than a 4 lane highway with cars eery few seconds. Animals know to get across a clearing as quickly as possible if they do better inside the forest. Birds, especially, fly low across roads because of much older threats than traffic: Hawks, Eagles, and Owls.
The highway is not the only barrier to crossing for animals and even plants. The opening of the road offers sunlight to plants ready to take advantage of it. This is why we experience forests as a thicket of thorny bushes and vines, concealing an open understory beyond. The vines and shrubs that occupy edges have been doing that for millions of years, at the edge of tree falls. Now, the edge in America’s forests has increased a thousandfold.
The road and the highway remain a harsh environment for animals and plants of all types. On my 14 mile commute home today, I saw an owl or an eagle (I couldn’t tell at 35 MPH) laying like a clump of jetsam in the other lane of the offramp. I thought it was a bird, but wasn’t sure until I saw in my rear view mirror flapping up before crashing back down with the next passing car. Below freezing, it is not a good night for a wounded bird in the middle of the road.