184 THE SWANS 



birds occasionally pausing to lightly brush their plumage with their 

 heads. Meantime the hen sinks lower and lower in the water till 

 actual pairing takes place, and almost immediately afterwards the 

 two face one another on the water, their breasts almost touching, 

 and the male easily distinguishable by his partially lifted but closed 

 wings. 1 Both birds then wash and dress their plumage. 2 The 

 nesting-habits have already been treated in the " Classified Notes," 

 but a few points of interest may be added. A new nest is built every 

 year, generally within a few yards of that of the previous season ; and 

 as it is generally close to the water it is liable to be washed away by 

 a sudden flood. Many cases are, however, on record in which both 

 sexes have worked vigorously to raise the nest when a sudden rise 

 has taken place in the water-level and the nest has been in danger of 

 being swamped or carried away. The eggs are not laid on consecutive 

 days, but with an interval of a day between each, and the pen will 

 often cover them up with loose nesting material when leaving the 

 nest to feed. This covering is carefully removed by the cob on taking 

 her place. As the pen will not resume her position till thoroughly 

 dry, the cob takes charge of the eggs in the meantime, and often 

 shows himself very reluctant to leave. Close observation shows that 

 there is considerable variation in the time during which the pen leaves 

 the nest to feed. Some birds will hardly leave their eggs at all, and at 

 the end of the incubation period are little but feathers and bones ; 

 others will remain off for hours together. It is a remarkable fact that 

 in several cases two swans have to all appearance paired in the 

 ordinary way and settled down to the business of nesting, when it 

 has been discovered either that a surprisingly large number of 

 infertile eggs have been laid if both birds are pens, or that incuba- 

 tion is apparently taking place for short intervals only in an empty 

 nest when both are cobs. 8 During incubation the male bird, while 



1 This attitude was erroneously taken by Naumann for the pairing position, which, however, 

 does not differ from that of other birds. 



* See O. Heinroth, Beitrage zur Biologic, namentlich Ethologie u. Psychologic der Anatiden, 

 an excellent piece of observational work. 



3 Cf. Whitaker, Zoologist, 1885, p. 263 ; and Heinroth, t. cit. 



