274 



SEA-BIRDS 



? overlap between 

 e.g. snowi and C. airbo 

 „kaiurka ^^i J 



Fig. 50 

 Breeding distribution of the tystie or black guillemot, Cepphus grylle and its allies 

 and races. Apart from the black-winged guillemot, Cepphus carbo, the Pacific races 

 are considered to belong to C. grylle, though many American workers separate them 

 as the pigeon-guillemot, C. columba. Black lines embrace probable extent of 

 breeding range; black dots represent some known breeding-places. 



of the cliffs ; but often the pair separate soon after leaving the cliffs, 

 and one may alight on the sea while the other flies on. 



When assembled in early spring on the water below the breeding 

 rocks and cliffs auks carry out mutual display, in the form of "water- 

 dances." Razorbills and guillemot pairs will swim around each other, 

 at the same time opening the mouth to display the coloured interior 

 and uttering guttural cries. The head is thrown back and upwards 

 with a jerky action, repeatedly. The other bird may show little interest 

 in this display, but usually keeps swimming so that it is face to face 

 with its partner: or both birds may display mutually, and a third or 

 fourth may join to form a circle of displaying birds. These water- 

 dances differ somewhat in each species. A party of razorbills or 

 of black guillemots will often form a line, sometimes two parallel 

 lines, swimming in this formation "line ahead" for short distances. 



