22 



SEA-BIRDS 



Fig. Q.a 

 The breeding sea-birds of the North Atlantic, arranged by five 

 geographical regions. No species breeds in more than four. Number 

 of species; see opposite page for actual species 



included, those belonging to families whose fundamental evolution 

 has ])robably been non-marine (like anatids and waders) or which are 

 only sea-birds in winter (divers and grebes). Only the more important 

 of these are on the diagram, and they are not otherwise treated in this 

 book. It is interesting that more than half of them are northern ducks 

 which winter at sea, though usually within sight of shore. 



It must also be pointed out that several species belonging to the 

 families of primary sea-birds have secondarily taken to life inland, 

 on rivers, or on estuaries, and may reach the sea only incidentally 

 or not at all. Certain West African species, in particular, are river- 

 birds (the pelicans Pelecanus onocrotalus and P. rufescens, the reed- 

 cormorant Halietor africanus^ the darter Anhinga rufa, the skimmer 



