You may think the sunstroked Arizona deserts are sparse, open, nakedly exposed, but the Sonoran Desert of southern Arizona is the most densely vegetated desert in the world — it is positively verdant. Desert animals are dependent on this cover, and many will not cross denuded open ground, so roads are de facto biological borders for these species, fragmenting their populations and separating them from needed shelter, water, food, mates. The mere presence of a road can, in itself, make an area uninhabitable.
For larger wide-ranging species like deer, bear, mountain lions, coyotes and antelope, critter/car collisions are of concern to the authorities, and are probably the main reason that the state of Arizona is now constructing wildlife tunnels and overpasses to provide safe passage across roads.
But much study has been done in southern Arizona on wildlife corridors that link the region’s Sky Island mountain ranges. These corridors save mountain species from isolation on these aptly named desert ranges, allowing genetic diversity to be maintained. Pima County, which includes the city of Tucson, is buying up land in these corridors to keep them functional, and save them from the (now busted) development frenzy that, in just the last few years, has gobbled up hundreds of thousands of acres. This is in accord with Pima County’s truly visionary Sonoran Desert Conservation Plan, which is specifically aimed at preserving biodiversity within the county.
So in Pima County, because of the studies and the saved land, the new wildlife tunnels and overpasses are being built in the corridors where they are most effective.
What the folks in Arizona are doing can be replicated and writ large over the whole of the American landscape. That is the vision of the Rewilding Institute, some of whose principals advised Pima County on their conservation plan. The Rewilding Institute envisions big, deep wilderness areas with connecting corridors across the whole of the Americas — a heart-stoppingly romantic and, it seems to me, doable project. Stop by their site or any of their affiliates and allies and marvel at the beauty of their dream. Better yet, help them achieve it.