What Do Culverts and Lemons Have in Common?

The development of transportation networks in the United States is the largest public works effort to ever be pursued, and has redefined our nation’s landscape.  Photo by Grant Hutchinson via Flickr Creative Commons

As a society largely dependent on transportation infrastructure for the movement of people, goods, and services, the negative ecological consequences of transportation are inevitable. From noise and chemical pollution to habitat modification, the footprint of roads and vehicular traffic pose a threat to intact ecosystems and wildlife.

The ecological effects of transportation are numerous, including habitat loss, habitat degradation, and mortality due to wildlife-vehicle collisions (WVC). By fragmenting the landscape, roads create a barrier for wildlife movement and the exchange of natural processes. However, there is hope!

Recognition of these impacts is spurring conversation all over the world on how to avoid, minimize, and mitigate the ecological impacts of transportation networks. How can the connectivity of landscapes be enhanced and the risk of WVC reduced? With the opportunity to construct new infrastructure, ecological considerations including natural areas, wildlife corridors, and critical core habitat can better inform road siting. New crossing structures can even be designed specifically for wildlife passage. But what is there to say for existing infrastructure?

Did you know?

The combined length of roads on earth is enough for 83 trips to the moon and back!

As an optimist myself, I’ve always jived with the saying, “When life hand you lemons, make lemonade.” You’re probably wondering, what does that have to do with anything. Well in the case of existing transportation infrastructure, it has everything to do with it!

Rather than seeing transportation infrastructure as a barrier, we can instead look for opportunity. Culverts and bridges can pass more than just water under roads – these structures can function to pass terrestrial wildlife as well.

However, not all structures and structural attributes are suitable for all species. For example, large boulders used to armor banks under bridges, also known as riprap, do not provide a suitable footpath for ungulate species, like moose and deer. Similarly, some species, like bobcat, would prefer to not have to get their paws wet while crossing through an underpass.

LittleRiver Wildlife Shelf in Waterbury, VT by VTrans

To entice species like moose and deer, the VT Agency and Transportation and VT Fish & Wildlife Department retrofitted a series of bridge banks, formerly stabilized with riprap, with wildlife “shelves” using sand and soil left over from other highway projects. Photo by VT Agency of Transportation

Bobcat Crossing Under Culvert by VTFWS

A bobcat avoids the water by taking to a ledge as he crosses through a culvert under Route 114 in Glover, VT. Photo by VT Fish & Wildlife Service

In Vermont, the National Wildlife Federation’s Northeast Regional Office is working with a host of local partners to characterize the use of culverts and bridges as a pathway for wildlife movement under roadways. With the help of wildlife cameras and tracking techniques, we are monitoring wildlife activity at and surrounding a variety of culverts and bridges throughout VT.

Moose near culvert in Elmore, VT by NWF

This moose was spotted trolling the habitat west of a culvert being investigated for its potential to pass wildlife. Photo by NWF

Documenting wildlife behavior in this manner will allow us to assess individual species’ preference for structural characteristics and define which structural and landscape characteristics facilitate in the movement of wildlife across the landscape. This in turn will allow us to differentiate between structures that are currently functional for wildlife passage and those that are not.

With small alterations, many of our existing culverts and bridges can be improved in a timely and economically feasible way to provide greater permeability for wildlife.

By examining existing transportation infrastructure, NWF works with a diverse set of partners to inform the enhancement of culverts and bridges where wildlife movement is restricted. Together this work supports local transportation agencies in prioritizing improvement opportunities in a cost-efficient manner, so that new infrastructure constructed for the purpose of wildlife passage is invested in only as necessary. When life hands you culverts, make wildlife crossings!

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