In this whimsical charmer from New Zealand, a child named Mabel finds a duck on her doorstep--a duck that makes it clear that it thinks it's a cat: it says ""Meow,"" drinks milk, and stalks mice. Determined to straighten it out, Mabel provides properly labeled pictures (some of them from familiar illustrators) and finally points out, when the duck has been chased up a lamppost by a dog, that, as a duck, it can fly down. So it does, and ""You were only joking, weren't you?"" says Mabel. ""Quack,"" says the duck. Last scene: a cat turns up, remarking ""Quack."" The spare, repetitive text is deliciously understated and easy enough for beginning readers. Nature illustrator Gaskin, new to picture books and to Americans, makes the dogged duck's ""odd"" behavior seem altogether plausible, nicely amplifying the humor in the carefully chosen details of his realistic watercolors. Amusingly offbeat, with pleasantly mind-teasing undercurrents concerning logic and identity.