EEITISH WARBLERS 



correspond. Each year we are learning more about geo- 

 graphical races; we find slight differences in structure and 

 colour where previously none were supposed to exist, and 

 these peculiarities seem to be common to all the individuals 

 of a species inhabiting a certain area. We also find 

 peculiarities in the song of the same species in different districts. 

 And if there are differences in structure, colour, and song, 

 why not in the nervous system ? It is generally, and probably 

 rightly, supposed that the instincts of a species are more or 

 less constant throughout the whole of its range. A motor 

 reaction, however, is part of an emotion, and an emotion, 

 though it accompanies an instinct, is a separate manifestation. 

 An instinct is uniform just because it is of vital importance 

 to the species as a whole and therefore subject to a rigid 

 selection. But it is possible that these reactions may not 

 be of selection value, and consequently subject to a greater 

 variation than we imagine. 



Before finally leaving this interesting phase of the bird's 

 behaviour, we will analyse a little more closely the relation 

 of attitude and vocal extravagance to emotion. This is a 

 somewhat difficult undertaking, involving as it does the 

 dangerous proceeding of attempting to put oneself in the 

 place of the bird. Nevertheless it is important that we should 

 attempt, as far as possible, to separate these activities, to 

 trace out the emotion to which they correspond, and instead 

 of taking a broad view of the behaviour as a whole, make some 

 effort to reduce it to order. We are accustomed to use the 

 term "display" to embrace the whole of the visible signs of 

 the complex emotional system of a bird, and if there are facts 

 which seem to be outside its province we find for them a ready 

 explanation under the heading of "play" — practice, that is 

 to say, for the more serious side of life. But we can scarcely 

 make use of so loose a definition as "display" if we desire to 

 resolve this emotional behaviour into its constituent parts. 

 Let us take the song first, and for this purpose it is only 

 necessary to consider it in its more emotional aspect. Violent 



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