46 



SEA-BIRDS 



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^orsteri^ 



M^ 



__ •Virgin Is. 

 .Uommica. 



>fc\ 



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Jo> 



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Fig. 7 

 Breeding distribution of three closely-related terns: Sterna hirundo, the 

 common tern; S. paradisaea, the arctic tern; S.forsteri, Forster's tern. Areas 

 of overlap shaded. S. h. turkestanica is a doubtful subspecies 



from very light phases with yellow over their ears and the back of their 

 necks, white throats and bellies, to those which are almost uniformly 

 brown. The breeding fulmar population of Britain, the Faeroes, Ice- 

 land, Jan Mayen and West Greenland are all light-coloured with 

 white bellies, necks and breasts, but in Baffin Island, Spitsbergen and 

 Franz Josef Land the fulmars are nearly all very dark coloured. 

 Between the light forms of Britain, etc., and the dark forms of Spits- 

 bergen, there are a number of puzzling intermediates, most in evidence 



