Pathways for predators, prey, humans

One morning as I was walking down a country road, a bobcat crossed ahead of me. I barely saw it because, instead of running over the blacktop, it dashed under the road through a narrow culvert, pausing on the other side to watch my approach before disappearing into the deeper cover of the woods. The channel was dry and the diameter of the tunnel no wider than a large pizza. There was no barrier to it going over the top. It clearly preferred the option of keeping to the shadows.

Wildlife corridors crisscross the landscape, making use of habitat connections in the built environment as well as those provided by nature. Culverts are frequently barriers, both for in-stream movement of fish and other aquatic creatures and for animals that might otherwise find their way through in the shallows. A predator like a bobcat or fox might use them under the right conditions, as my experience confirms, while prey species prefer to know what is lurking.

Culverts come in many sizes, their primary function to move volumes of water from one place to another. Those that are too narrow risk failure in the major flood events that climate change is likely to increase. 

Those that are perched with a plunge of water at the outflow prevent trout and other fish from moving upstream when temperatures get too warm in the stretch of water below. Assessing which culverts are both significant barriers to wildlife and at greater risk of failure during high water flow may represent an opportunity for conservation and transportation priorities and resources to align, creating better designs for the replacement infrastructure that can meet both objectives. 

Culvert assessments with this in mind are underway in a number of communities in our region lead by the Housatonic Valley Association (my employer) in association with state and local partners and municipalities.

I was on another road a few weeks ago, this time in a rural part of Torrington. I walked over a bridge that crossed the East Branch of the Naugatuck, and went down for a closer look. The bridge was wide enough to include a good section of bank on either side, with clear signs of animals passing through in safety. 

The river had a natural bottom, with rocks and pools, rather than flowing in a sheet across a concrete slab: effective for in-stream migration. This was no barrier, for cars, water or wildlife. Not every crossing can be enhanced to this degree, but where options exist to accommodate our habitat and the needs of the animals that share it with us, we ought to take advantage of them.

Tim Abbott is program director of Housatonic Valley Association’s Litchfield Hills Greenprint. His blog is at www.greensleeves.typepad.com.