STRUCTURE AND SEA-BIRDS OF THE N. ATLANTIC 21 



in Morocco, reappears as a new race, primarily South African. The 

 bird communities of these islands are only moderately well-known. 

 Most of the sea-birds nest on rocks whose comparative inaccessibility 

 has been both a temptation and a deterrent to the visiting ornithologist. 

 As for the coast of West Africa and the islands lying close to it, no 

 organised investigation of the sea-bird communities of this difficult 

 region has yet been made. We know that one group of species breeds 

 on the Atlantic African coast to Morocco, but no farther south — 

 the shag, herring-gull, the whiskered tern, probably the gull-billed 

 tern, possibly the slender-billed gull. Farther south both white and pink- 

 backed pelicans, Pelecanus onocrotalus and P. rufescens, and the grey-headed 

 gull. Lams cirrhocephalus, reach the tropical sea-coast in some places, 

 and the brown booby nests on at least one island off the coast of 

 French Guinea. The Caspian tern, whose world distribution is, to 

 say the least, peculiar, may have breeding stations on this coast, and 

 the little tern, which we had left behind in Morocco, reappears as a 

 separate race on the coast and rivers of the Gulf of Guinea. 



The African darter, Anhinga rufa, reed-cormorant, Halietor africanus, 

 and the African skimmer, Rynchops flavirostris, haunt the rivers and in 

 places reach the coast; but they are not sea-birds: and on islands in the 

 Gulf of Guinea the noddy and the white-tailed tropic-bird, Phaethon 

 Upturns, breed. It is suspected that the frigate-bird may nest on this 

 coast, but its breeding-place has not been found. Neither has that 

 of the bridled tern. Sterna anaetheta, or the sooty tern, S. fuscata, although 

 both species are seen in considerable numbers. There is at least one 

 other riddle: a population of the royal tern, Thalasseus maximus, 

 haunts almost the whole coast of West Africa from Morocco to some 

 hundreds of miles south of the Equator. Systematists have separated 

 it from the West Atlantic population as a subspecies {albidorsalis) , on 

 valid differences, and it does not appear to leave this coast, yet no 

 ornithologist has yet seen its nest or even its eggs. 



Only in the tropical parts of the Atlantic are there still these distribu- 

 tional queries. In the temperate and arctic zones the breeding places 

 of the birds are well-known and described. And with this little mystery 

 we conclude our tour of the Atlantic, for we are back on the equator 

 and can strike west to the St. Paul Rocks, where we began. 



The sea-birds of the North Atlantic can be listed in the form of a 

 table (Appendix, p. 292), and plotted according to which parts 

 of the ocean they breed in, in the form of a diagram (Fig. 2) . For 

 the purpose of completeness, the secondary sea-birds have been 



