250 THE MIGRATION OF BRITISH BIRDS 



migration from the south begins to assume a graduallj- 

 increasing strength, which continues to swell in volume 

 as the month progresses, and with most species to be 

 continued well into May. Daily the numbers of Chiff- 

 chaffs, Willow Wrens, Whinchats, Redstarts, Wheatears, 

 and Warblers increase. It is chiefly owing to the 

 observations made at the points where migrants enter 

 our area that we are able to compute the duration of 

 the flight of these species. From these records, extend- 

 ing as many of them do over a long series of years, we 

 are able to judge pretty accurately not only the duration 

 of the migration of each species, but the time it begins 

 and ceases. We are thus able to state that the migration 

 of all birds that begins in April is continued into May, 

 and much more exceptionally into June. With such 

 species, however, as the Honey Buzzard, the Garden 

 Warbler, the Lesser Whitethroat, the Wood Wren, the 

 Cuckoo, the Turtle Dove, the Quail, the Red-necked 

 Phalarope, the Common Sandpiper, and all the Terns, 

 the migration is much stronger in May than in April. 

 Probably all the birds that breed in our islands have 

 reached every part of them towards the end of May. 

 The migration, however, of some of the common summer 

 migrants continues into June. We have ample evidence 

 that such species as the Whcatear, the Swallow, the 

 House Martin, the Cuckoo, the Dotterel, the Whimbrel, 

 the Ruff, and the Arctic Tern continue to enter our area 

 in June (the Swallow especially), but there can be no 

 doubt whatever that these late individuals arc coasting 

 across the British Islands on their way to more northern 

 breeding grounds, and in most cases pass by other 

 individuals of the same species already engaged in the 



