DISTRIBUTION OF THE GULLS AKD TERNS. 395 



from Alaska to Japan. It is, however, only in the North Pacific 

 and North-western America that we find L. glaucescens, a gull 

 of similar dimensions but with faintly barred primaries, which 

 give it in effect the appearance of a washed-out Herring-gull 

 {L. argentatus). It is a perfectly recognizable species, but it is 

 clear that it forms a connecting-link between these two groups ; 

 and as it is well-established that the Herring-gulls which are 

 resident furthest north are lighter in colour than southern ex- 

 amples, it is not difficult to trace out the gradual diminution of 

 colour through i. glaucescens, till the total loss of it is reached in 

 Ij. glaucus and L. leucopterus. In the Herring-gull group, again, all 

 the forms — call them species or varieties — are found in the North 

 Pacific. It is there that we meet with L. argentatus of our islands, 

 Western Europe, and North America, as distinguished by its pale 

 flesh-coloured legs and pale eyelid from L. cachinnans, with its 

 slightly darker mantle, yellow legs, and bright brick-red eyelids, 

 which takes the place of L. argentatus in the Mediterranean, over 

 the steppes of Russia and Siberia, and coasts of Asia, and reaches 

 to the Pacific seaboard of China. L. affinis, Eeinhardt, with a yet 

 darker mantle and wings, which, however, still show a distinct 

 pattern in their outer primary feathers, is also to be found in the 

 North Pacific. The explorations of Messrs. Seebohm and Harvie 

 Brown on the Petschora have shown us that this last species 

 merely visits Northern Europe and Siberia to breed at a time when 

 there is an almost continuous sunshine, whilst the rest of the year 

 is passed in the brilliant atmosphere of the lied Sea and the coasts 

 from thence to India. Bearing in mind the gradual increase in 

 intensity of colour in proportion to the amount of continued sun- 

 shine experienced by all these gulls, and the increasing pallor 

 amongst the species which mainly inhabit the north, it seems 

 impossible to avoid the deduction that many of these varieties 

 which we agree to call species are almost entirely due to climatic 

 influence. Of the three species named, two are, however, exclu- 

 sively Palsearctic ; but on the American side, from Vancouver's 

 Island to Lower California, is found another species, L. occi- 

 dentalis, Audubon, a gull with a very dark mantle, no pattern 

 on the outer primaries, and a short stout bill; this is an ex- 

 clusively American form, but it is clearly a member of this 

 group. 



"With the same range as L. occidentalism and restricted, like it, 

 to the western side of the North Pacific, is found L. californicus, 



