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IF YOU ever find yourself on the Trans-Canada Highway in Banff National Park, keep an eye open for odd-looking bridges. They are covered in bushes and trees as if they have fallen into disuse. Anything but: these are grizzly bridges and they are a vital artery allowing bears and other wild animals to cross. They have been so successful that more will now be built to help North America’s wildlife roam free (see “Conservation: time to think big”). It’s a small step, but a timely reminder that it is still in our power to make good some of the damage we do to the natural…