loo Huxley, Bird-watching and Biological Science. LApril 



Display and coition go on until all the eggs are laid, and incubation 

 then begins. This is usually a duty of the hen bird, and the cock 

 generally continues singing till the young are hatched. As far as 

 the race is concerned, the cock's song is to attract a mate and then 

 probably help stimulate her; but as far as the cock bird himself is 

 concerned, song is simply an outlet, and a pleasurable one, for 

 nervous energy; thus, provided certain internal physiological 

 conditions are fulfilled, he will continue to sing in all moments of 

 excitement or exaltation, non-sexual as well as sexual.^ After 

 hatching-time however, it is necessary that he help feed the young, 

 and his nervous energy being thus diverted, his song ceases. 



In these birds, it appears to me that we are being shown some of 

 the primitive things of courtship. In this, Mr. Pycraft and myself 

 are, I think, agreed; to both of us the "display" of the male 

 Warbler is nothing but a direct expression of sexual excitement, 

 scarcely, if at all, modified by Darwinian Sexual Selection — 

 nothing but the way in which nervous disturbance caused by 

 sexual excitement happens to liberate itself. General nervous 

 discharge will cause general muscular contraction; and something 

 approaching this is here seen — rapid hopping, extension and 

 fluttering of the wings, spreading of the tail, bristling up of the 

 feathers on head and throat, and the utterance of a series of quick 

 sounds. This expresses a condition of readiness to pair, and 

 doubtless to the female comes to be a symbol of the act of pairing. 

 Hence, as far as the female is concerned, the act of pairing has 

 come to depend upon this stimulus (acting of course on a suitable 

 internal physiological state). This is no more strange in the bird 

 than it is that in ourselves thoughts and emotions of love well up 

 at the sight of some tangible object connected with the beloved. 

 The main difference between the Grebe and the Warblers in this 

 respect is that in the Grebe both sexes are equal in their affection 

 and also in their eagerness, while in the Warblers the hen, as 

 evidenced by her behavior, is most obviously less eager than the 

 cock. 



An extremely similar form of courtship, especially as far as the 



1 As is well known, many birds sing under the influence of anger (e. g. the Reed-warbler, 

 Acrocephalus slreperus), or as a resuU of a sanse of general well-being (e. y. Song-thrushes, 

 Tardus musicus), on warm days in winter. 



