"The s mark where they have been and once one has learned to read sign, as woodsmen and professional ornithologists do, one can study food habits. Meat and fishing-eating birds pass conspicuous white urates, commonly called whitewash, and they regurgitate pellets. The splashes of whitewash under a perch suggest that a bird of prey may have used the perch. s, for example, also pass their urates in the form of whitewash, but if the perch is far from a body of water or from a heron rookery, the whitewash was probably passed by a hawk, an owl or a crow. The whitewash of hawks is rather splashy and falls in spatters and streaks. That of owls is far more solid, chalky in texture and tends to form little heaps. Owls tend to gulp their food in big mouthfuls, swallowing many bones—large and small—along with meat. The bones, only slightly digested, persist in the pellets of adults. One can learn a great deal about what owls have eaten by examining the contents of pellets carefully."