252 THE MIGRATIOX OF BRITISH BIRDS 



in February and certainly lasts until the end of May or 

 the first week in June. In some cases the migration of 

 a species extends over the entire period, as for instance 

 the Wheatear ; in other cases the flight does not cover 

 more than three months, and even then in a great many 

 instances the migration is weak at the beginning and 

 at the close of that period ; whilst in other cases the 

 migration is confined to two months, especially in such 

 species as the typical Warblers, the Wagtails, and the 

 Pipits. Other species limit their spring migration to a 

 month. Among these we may include the Marsh 

 Warbler, the Red-backed Shrike, the Hoopoe, the Red- 

 necked Phalarope, and the Greenshank. As a general 

 rule we might say that the most widely-dispersed species 

 cover the longest period in their migrations, the most 

 local birds the shortest period, the length of flight-time 

 being in the same ratio as the dispersal of the species. 



A few words concerning the Vertical Migration in 

 spring now become necessary. This migration is just 

 as characteristic and as marked a feature of the spring 

 in mountain districts as that taking place in a latitudinal 

 direction. The duration of the period also is about the 

 same, and lasts for about four months, although it is not 

 perhaps so marked at the beginning or at the close. 

 The movement is more contracted, more rapid. Amongst 

 the earliest of these vertical migrants we may instance 

 the Stonechat, the Linnet, the Gray Wagtail, the Wood 

 Lark, the Sky Lark, and the Lapwing. These species 

 begin to move up the hills in February, but the migration 

 is much more strongly marked in IMarch, and dies com- 

 pletely away during April. The next birds to move 

 are such species as tiie Merlin, the Linnet, the Twite, 



