27 July 2010

Deer Cross Here

Why did the chicken cross the road?

One of the largest problems with wildlife habitat is the problem of fragmentation. This is where a block of forest or plains or marsh is split into smaller pieces. This fragmentation can be caused by farmland, housing, or forestry, but most often occurs due to roads and is even a large problem in natural reserves. Roads represent an extremely dangerous crossing for most wildlife, as well as drivers, primarily due to collisions with vehicles. They also cause problems by splitting up wildlife populations (small groups of animals are more vulnerable to being wiped out than large groups), degrading habitat close to roads due to maintenance and pollution, and preventing access to resources on the other side.

Because there wasn't a bridge!

(Joel Sartore)
This problem has been tackled a few different ways. Underpasses that allow wildlife to cross beneath roads have been created for creatures who don't mind dusty, dark, enclosed spaces, such as turtles and raccoons. Large enough underpasses have even been used by deer and moose! However, large carnivores such as wolves, cougars, and bears generally don't like them. So if you can't go under, let's go over! Many wildlife-conscious areas, such as Banff National Park in Alberta, have begun installing wildlife crossing bridges or "green bridges" as they are often called. First installed in France in the 1950's, these are usually wide bridges planted with grasses and small shrubs with fences along the edges.


Green bridges have been shown to help lessen the effects of fragmentation and to decrease the number of vehicle collisions with large mammals by an average of 86% close to where the bridge is in place (sec. 4.4). They are currently being used in many areas with a high rate of success. In Florida, several underpasses have distinctly lowered the casualties of florida panthers on highways where they have been installed. Not just for roads, overpasses over a deep irrigation canal in Arizona have decreased the number of deer and other animals from getting stuck and drowning in the canal. Researchers have picked out tons of road kill "hot spots" that could benefit from crossings, but it's still a matter of time and money until they're considered everywhere.


  1. Jennifer Lapp27 July, 2010 14:19

    i'm loving your blog.. I am learning something new. Thanks for helping me keep up with the lapp clan.

  2. I think I've read studies on this sort of thing before that predation around such bridges increases and can have a negative effect on prey species in the area that are trying to move. Any thoughts on that?

  3. Hrm, you make a very good point, Meagan. I would assume it would be much like feeding plots, in that it would increase predation and the spread of disease, but I could actually find absolutely no papers on how much or if they increased at all! I guess we're still in the testing stage and we're still simply studying how much wildlife crossings are used at all. It would be interesting to know if the increase in survivability from fewer collisions is negated by an increase in disease and predation. I'll keep my eyes out for any studies along those lines.

  4. This was super interesting, and I hope they put one between Point and Wausau ;)

  5. It's too bad they can't just enclose the entire roadway. Not only would it defrag the ecosystem, but they wouldn't have to plow or clean up. At least they wouldn't have to clean up anything but carbon monoxide related deaths.

    Added bonus: The zombies could possibly be corralled in to the tunnels and then hit with napalm.

  6. I feel like funneling the zombies into a tunnel and lighting them all on fire is a slippery slope. Before you know it, you'll have a highway-sized flaming zombie cannon pointed directly at major cities...