Observation, the gift of, 90; alertness of mind necessary in, 118, 286; a translation of nature's language into human speech necessary in, 118; on the part of wild creatures, 119; selective and detective, 208, 211; an unbiased mind necessary in, 252; specialized, 252, 253; all possible sources of error to be taken into account in, 253; a steady and patient as well as sharp eye necessary in, 262-269, 286; love of nature the first step in, 283; the critical habit of mind necessary in, 291. Oriole, Baltimore (_Icterus galbula_), 236-238, 286; nest and eggs of, 65, 66, 124, 237, 238. Osmunda fern, royal, 16. Osprey, American, _or_ fish hawk (_Pandion haliaëtus carolinensis_), regular habits of an osprey, 172, 173, 257. Ostrich, 86. Otter, American (_Lutra hudsonica_), tracks of, 303, 304; habits of, 304. Oven-bird. _See_ Thrush, golden-crowned. Owl, great horned (_Bubo virginianus_), 197; nest of, 61. Owl, screech (_Megascops asio_), a brood of young, 294; notes of, 220; nest of, 61. Owl, snowy (_Nyctea nyctea_), 197. Owls, the eggs of, 62, 198. Oxen, 99, 100. Panther Mountain, 43, 56, 57. Partridge. _See_ Grouse, ruffed. Peak-o'-Moose, 43. Peeper. _See_ Hyla. Perch, 16, 212. Phœbe-bird (_Sayornis phœbe_), 286, 293, 294; nest and eggs of, 62-64, 70, 249, 260, 297. Pickerel, 16. Pigeon, passenger (_Ectopistes migratorius_), 101; nest of, 62. Pike, barred, 212. Pink, prairie, 98. Pitcher plant, 6. Polygala, fringed, 20, 21. Pond-lily, 15-18. Porcupine, Canada (_Erethizon dorsatus_), 36, 37, 47, 53, 58, 309. Prairie, the, notes from, 87-109; like the ocean, 88; life in the fifties on, 97-107; game on, 101-107; a _dead_ level, 224. Prairie hen. _See_ Grouse, pinnated. Primrose. _See_ Evening primrose. Proctor, Professor, 224. Pussy-willows, 220. Quail, _or_ bob-white (_Colinus virginianus_), 101; setting, 136; young of, 137; answering a call, 175, 176; hatching of the young, 291, 292; notes of, 175, 176; nest and eggs of, 75, 135-137, 291, 292. Rabbit, 48. Rabbit, gray (_Lepus sylvaticus_), 176; a captive, 182, 183; timidity and witlessness of, 197, 198. Raccoon (_Procyon lotor_), 163; a captive, 178, 179; courage of, 196, 197. Rain, in camp, 48. Rat, pet squirrel and, 96, 104. Red-bird, summer, _or_ summer tanager (_Piranga rubra_), 236; song of, 236. Rhexia. _See_ Meadow-beauty. Roads, in Kentucky, 232.