Schaefer, best remembered for the invincible Shane, has used the new 20th century ethological approach--""the study of living creatures leading natural lives""--in this respectful differentiation of the animals monitored, obviously with great patience and intelligence, in the vast backyard of his native Southwest. And while he's also read widely from Pliny to Ardrey, Linnaeus to Huxley, and can put the right taxonomical tag on any critter--he's more interested in personalizing their variously ingenious, adaptive capabilities. He's never slavishly sentimental--after all the opossum, our only marsupial, is ""wonderfully stupid"" and the gopher's a ""confirmed grouch."" Many, many unfamiliar faces and strange shapes dart in and out of the mesquite in a work of easy, affectionate observation and contemplation. Schaefer's bestiary should have a long life cycle ahead, scaled for all sizes and ages.