As the author of ''Pecked to Death by Ducks,'' Cahill sure knows how to accentuate local color. Despite the relatively tame title, his latest batch of travel/nature essays is no different. The backyard in question is Yellowstone National Park, and Cahill takes us down a lot of less-beaten paths that embrace the enormity of North America's ''Serengeti Plain.'' With his typically offhand wit, he assesses the danger of indigenous bison, which ''may seem indolent, even lazy. But then they abruptly decide you need to be gored.'' Almost as casually, he mentions that Yellowstone sits atop a boiling cauldron of volcanic activity that, by some calculations, could blow any day now and pretty much end the world. Scary as he makes the place seem, you'll want to get there. Like, yesterday.