122 ESSAYS OF A BIOLOGIST 



come up to them with their stone offering and lay 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 court- 

 ship, but content themselves, apart from this presenta- 

 tion of household material, with what Dr. Levick 

 describes as ' going into ecstasy ' — spreading their 

 flippers sideways, raising their head quite straight 

 upwards, 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 applied 

 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 

 emotion. 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 

 violence 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 courtship. 



Or, again, the actions may be performed for their 

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



