2l6 THE BIRDS OF THE BRITISH ISLES. 



but the lighter L. f. affinis Reinhardt, breeds in the British 

 Isles, the Fa;roes, western France, and perhaps elsewhere ; 

 both races are migratory, and both occur on passage and, 

 occasionally, as winter visitors. How frequently the dark bird 

 occurs is not certain, for it is often difficult to judge the depth 

 of shade of a flying gull. The winter range of the two forms 

 is not known with certainty, but that a large number of our 

 birds leave is proved by the frequent recovery of ringed Lesser 

 Black-backs in France, Spain, Portugal, and north-west Africa. 

 The largest colonies of the British bird are in Scotland, 

 Ireland, the north-east and western shores of England, and 

 Wales. 



The Lesser Black-back is a smaller and slighter edition of 

 the Great Black-back, but differs from both this and the 

 Herring-Gull in its yellow legs. In immature plumage, though 

 at first it closely resembles the Herring at the same age, the 

 darker mantle soon becomes apparent. In spring and summer, 

 especially near nesting colonies, this gull is common, though 

 never so abundant as the Herring-Gull, but in spring and 

 autumn it is a far more familiar bird inland, for there are 

 regailar overland as well as coastal migratory movements. 

 From about the middle of March until June birds are going 

 north, and from July or August until October, passing south. 

 In inland localities the birds often travel singly or in twos or 

 threes, but on the Yorkshire coast, early in October, I have 

 seen huge passages. On October 6th, one year, Lesser and 

 Great Black-backs passed practically continuously from 9 a.m. 

 till 6 p.m., often 50 to 100 at once ; the smaller birds far out- 

 numbered the larger. After timing the birds at intervals I found 

 that the average rate was about 50 per minute ; 20,000 a day 

 was a low estimate, and this passage continued for over a week. 

 Most of the Lessers came in from off the sea, from the north- 

 east, but at that time I was unaware of the racial characters. 

 In sprmg in Cheshire I see most birds passing between the 



