124 ESSAYS OF A BIOLOGIST 



it at the feet of the embarrassed or amused human 

 being. 



The Adelies do not nest by their natural element 

 the sea, but some way away from it on stony slopes 

 and rock patches; thus they cannot employ their 

 brilliant dives and feats of swimming in courtship, 

 but content themselves, apart from this presentation 

 of household material, with what Dr. Levick de- 

 scribes as 'going into ecstasy" — spreading their flip- 

 pers sideways, raising their head quite straight up- 

 wards, and emitting a low humming sound. This a 

 bird may do when alone, or the two birds of a pair 

 may make a duet of it. In any case, the term ap- 

 plied to it by its observer well indicates the state of 

 emotion which it suggests and no doubt expresses. 



The depositing of courtship offerings before men by 

 the Penguins shows us that there must be a certain 

 freedom of mental connection in birds. Here an 

 act, properly belonging to courtship, is performed as 

 the outlet, as it were, of another and unusual emo- 

 tion. The same is seen in many song-birds, who, 

 like the Sedge Warbler, sing loudly for anger when 

 disturbed near their nest; or in the Divers, who, 

 when an enemy is close to the nest, express the vio- 

 lence of their emotion by short sharp dives which 

 flip a fountain of spray into the air — a type of dive 

 also used as a sign of general excitement in court- 

 ship. 



Or, again, the actions may be performed for their 

 own sake, as we may say: because their performance, 



