WOOD WARBLER 



were dependent upon the periodic recurrence of a certain 

 organic condition in both sexes, it is probable that seldom only 

 would it reach its consummation ; if, on the other hand, the 

 necessary condition were always present in both sexes, no 

 check would be imposed upon a too liberal yielding to the 

 the sexual impulse. In order to overcome this difficulty the 

 sexual instinct is, I believe — though it is a mere supposition 

 on my part — allowed free play in the male, but is subject to 

 some periodicity in the female. Thus she may be said, 

 broadly speaking, to exercise a control, though such control is 

 really biologically determined. During the period of sexual 

 activity the male can usually be found in close proximity to 

 the female. She nutters from branch to branch, he following 

 in her wake, and as they roam thus about the territory in 

 search of food, she calls often and he utters the last sentence 

 of his song occasionally. Outbursts of excitement are of 

 frequent occurrence, and the male generally takes the initiative, 

 but not always, for sometimes the responsibility rests with her,, 

 that is to say it is she who suddenly and with but little warn- 

 ing darts off in pursuit. The routine of sexual behaviour 

 does not appear to be similar on every occasion ; I am 

 doubtful whether it is always initiated by a pursuit, but it 

 is difficult to speak with certainty upon this point. A mutual 

 pursuit amongst the trees seems, however, to be a necessary 

 part of the routine, and may even occur at the conclusion 

 of the whole process, subsequent that is to say to the comple- 

 tion of the sexual act. The normal procedure is as follows. 

 The male approaches the female, and settling beside her with 

 drooping wings commences to nutter or quiver them rapidly. 

 She may do likewise, whereupon both continue this wing 

 napping or wing quivering for a period which, though of short 

 duration, varies in length on different occasions. When the 

 proceedings are initiated by a pursuit, the male, previous 

 to darting at her, watches her intently for a few moments, 

 and whilst doing so betrays suppressed excitement, his 

 feathers being tightly compressed and his wings loosely 



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