Experience, acquired, 300 Experiments, removal of nests for, 181, 185, 190, 213, 214 Exposure, its effect on nestlings, 180 External environment, conditions in, 279, 282 Falcon, 48, 71 Feeding grounds, neutral, 125 in communities, 70 Females, fighting amongst, 109-118 ---- sexual impulse of, 13 Fieldfare, 124 Fighting instinct, 79, 82 Flight, emotional behaviour of Godwit during, 53 Flocks, in winter, birds collect together in, 262 Flycatcher, 244 Food, procuring of, 5 ---- abundance, or scarcity of, its relation to prosperity of young, 15, 16 ---- its bearing, on the movement of flocks, 262 ---- rearing of young dependent on rapid and regular, 179, 195 ---- supply, proximity to, necessary for rearing young, 179, 195 Fortuitous mating, 174 Fowler, Ward, on the value of communities, Rooks, 202 Fulmar, 121, 247 Functional activity, 259 ---- instinct of Reeve, 173 Functioning of the disposition, 275 ---- of the primary dispositions, 100 Garden Warbler, 223, 225, 230 Gätke, H., _Birds of Heligoland_, 24 ---- on the absence of song in birds on Heligoland, 124 ---- on the early arrival of Guillemots on Heligoland, 64 Godwit, emotional behaviour of, during flight, 53 ---- Black-tailed, 53 Grasshopper Warbler, 39, 131, 139, 153, 155, 187, 244 Greenfinch, 28, 33, 140, 235, 236 Gregarious instinct, 20, 61, 141, 265-66, 269, 276, 289, 290, 291, 296, 300 Grouse, Black, 63 Guillemot, Bridled, 64 ---- Common, 63, 64, 121, 192, 195, 206, 211, 247 ---- Ringed, 64 Gull, Common, 119 ---- Herring, 210, 278 Habit formation, law of, 8, 62, 65, 66, 67, 205 Hawfinch, 28 Headquarters, 176, 206, 207, 274 ---- restricted, 8, 9, 30, 50, 58, 64, 127 Hedge-Sparrow, 213, 221, 244 Hereditary equipment, 6 Herring-Gull, 210, 278 Hooded-Crow, 202 Hostility and territory, relationship between, 242 House-Sparrow, 218 Imitation, vocal, powers of, 156, 157, 161 Impulse, internal, 279 ---- to brood, 191 Inherited disposition, 5 Instinct, fighting, 79-82 ---- gregarious, 20, 61, 141, 265, 266, 269, 276, 289, 290, 291, 296, 300 ---- migratory, 37 ---- of song related to establishment of territory, 125 ---- sexual, reawakening of, 4, 18 Instinctive response, 180 Instincts susceptible to stimulation, 259 Internal impulse, 279 Internal stimulation, 62, 123 Interpretation of battles, 75 Intolerance of other birds, 218, 219 Intrusion resented, 274 Isolation, impulse to seek, 288 ---- of male, 12, 62, 65, 73, 81 ---- of male during breeding season, 267, 272, 273, 275, 281 Jay, 87, 156, 283 Kestrel, 228 Kittiwake, 116, 200, 247 Lapwing, 58, 59, 61, 62, 64, 84, 103, 104, 126, 189, 190, 220, 251, 284 Lapwing, life-history of, 58-61 Late arrival, advantages and disadvantages of, 33-44 Law of battle, 74, 75, 86 Lesser Whitethroat, 230, 244