STARLING IN SCOTLAND, INCREASE AND DISTRIBUTION 3 



may have had upon the allied subject of migration ? Again, 

 our later statistics show to us that a separate impulse appears 

 to have been given to a wave of dispersal from the south, which 

 advanced north along our south-west coasts and counties, and 

 then apparently to some extent retreated again. In con- 

 nection with these data we may ask the questions : Do our birds 

 which were formerly migrants only, but have since become 

 resident and breeding species within our area extend their 

 breeding areas, resulting from their autumn movements ; or 

 do they do so, resulting from their spring movements only ; 

 or do they do so, resulting from combined observations and 

 experiences gathered upon both spring and autumn journeys ? 

 (See under Dee and Caithness notes, infra, pp. 18 and 21.) 



We believe, after some study of migrational phenomena, 

 that there is a possibility that, as increase of breeding 

 area of a species extends along the longitudes between 

 north and south on the continents of Europe and Asia, so will 

 there likely be an increase of latitudinal dispersal along the 

 routes of migrants from east to west coming to the shores of 

 Great Britain from the Continent ; and resultant upon this, 

 at least in some degree, there may be a corresponding increase 

 of nesting localities north and south in our islands. Of this 

 we may perhaps instance the well-known increase of the 

 woodcock as a nesting species within the last thirty years, 

 extending even, as it now does, to the barren hills and hollows 

 of the Outer Hebrides. Thus, likely localities, viewed first in 

 autumn flight, and then again in spring flight, may be re- 

 visited and finally occupied, however long a period may have 

 passed before such became and continued as established 

 residences. 



Of a gradual pressure from congested centres within our 

 own islands we have already given instances in other places, 

 showing how lines of least resistance are followed, which are 

 equivalent, or nearly so, to occupation of the most likely 

 localities, first by a species pressing forward, though it has 

 never previously migrated over the country (see under 

 " Capercaillie in Scotland "). If congested centres occur 

 as they must do of certain species in Britain, congested 

 districts likewise, and under the same natural laws, must 

 also occur on the Continent, or on large continental areas ; 



