se, 63

Service, Robert, on flocks of unmated Sedge-Warblers, 44, 45

Sexual behaviour, 3

---- conflicts, 10

---- development, 6

---- function, discharge of, 2, 3, 26

---- impulse of females, 13

Sexual instinct in the migratory male, 26

---- of Reeve, 173

---- ---- reawakening of, 4, 18

---- life of birds, 1

---- maturity, males arrive at, before females, 36

---- organic change, 92, 123

---- selection, 166

Shag, 121

Shrike, Red-backed, 39, 50, 51, 156

Skylark, 188, 236, 244

Snipe, 153, 156, 219, 220

Sociability when not paired, 125, 126

Song, as an aid in searching for a mate, 12

---- its influence on mating, 167

---- origin of, 138

---- relation to reproduction, 123

---- relation to territory, 119-168

---- volume of, influenced by age, seasonal sexual development,
or isolation, 166

Song-Thrush, 222, 244

Sparrow, House, 218

Sparrow-Hawk, 269

Spring, at approach of, birds lose their shyness, 138

Stability of the water and mobility of the land, 260

Starling, 217, 218, 237, 251

Stimulation, internal, 62, 123

---- question of, 284

Stonechat, 87 187, 188, 189, 222, 233, 234

Stout, Dr, _Manual of Psychology_, 1, 77

Struggle for existence, 294

Susceptibility to position, 96

Swallow, 21, 156, 278

Territory, 1, 5

---- adjustment of, 10

Territory and reproduction, 169-214

---- breeding, 2, 3, 7

---- dates of acquisition of, 33

---- defence of, 6

---- desertion of, after rearing young, 276

---- disposition to defend, 73-118

---- disposition to secure, 6, 20-72

---- establishment of, 74, 285

---- evolution of, 176

---- failure to secure, 286

---- fights for, 10, 11, 13, 62

---- ownership of, 189

---- possession of, a stimulus to song, 136

---- its relation to migration, 259

---- its relation to reproduction, 169-214

---- readjustment of, 147

---- restriction of, advantageous for mating, 172

---- restricted, 8, 9, 30, 50, 58, 64

---- separate for male and female Cuckoo, 144

---- song, its relation to the, 119-68

---- temporary desertion of, 28, 35, 58, 59

---- and hostility, relationship between, 242

Thrush, Song, 222, 244

Tit, Blue, 221, 226

---- Great, 221

---- Long-tailed, 226

Tradition, 300

Tree-Pipit, 51, 188, 189, 222, 232,