CHAPTER 12 



TERNS AND SKIMMERS 



THE FORTY-TWO SPECIES in the subfamily Larinae/ or gulls, are 

 fundamentally northerly in their present distribution, and probable 

 evolutionary origin. The thirty-nine species in the other big subfamily of 

 the Laridae, the Sterninae or terns, are fundamentally tropical, and 

 there are more (thirty) species in the Pacific than in any other 

 comparable region of the world. However, there are a good number 

 in the Atlantic — twenty-three, or twenty-five if we include the Mediter- 

 ranean with it, and it is certainly not possible to conclude from the 

 •relative number of species that the Pacific is the evolutionary home of 

 terns; but it is likely that the adaptive radiation and evolution of the 

 terns has mainly taken place in the tropics. No less than nineteen 

 species breed on or near the shores of the smallest of the warm oceans, 

 the Indian Ocean. Seventeen species breed round the borders of the 

 North Atlantic. The breeding-distribution of only two species, 

 the arctic tern Sterna paradisaea and the common tern S. hirundo^ crosses 

 the Arctic Circle — that of the latter only in one small region. However, 

 four species breed in the cool climate of the cold waters of the Ant- 

 arctic Ocean. Many terns are birds of rivers or inland marshes — 

 nine species breed inland in Eurasia, six in North America, five in the 

 Indian region, and several inland in Africa, Australia and South 

 America. Some, like the black-bellied tern Sterna melanogaster of India, 

 Burma and Ceylon, or the common river-tern S. aurantia, which has a 

 rather wider distribution in the same region, or the yellow-billed tern 

 S. superciliaris of S. America, are exclusively, or almost exclusively 

 inland species. Others, on the other hand, like the noddy and fairy 

 terns (Procelsterna, Anoiis and Gygis) and the sooty tern Sterna fuscata 

 have very wide and very oceanic distributions, and many other Sterna 

 terns work into the pelagic and oceanic zones of the world's seas. 

 The majority of terns are white with, in spring, a black crown and a 

 grey back; a minority are darker, especially the less marine species. 



