THE FULMAR. 405 
population at the older centres further away to the north, 
and the far-reaching impulse of the first outward pressure and 
ever-gathering force afterwards as each successive colony in turn 
became overcrowded. 
This widespread and more general movement towards the 
south no doubt became accentuated and doubly enforced when 
the independent ranges of these ‘‘ northern hordes ” overlapped 
with that of the long separated and furthest south colonies of 
St. Kilda. The probable result, if these ranges did overlap, 
was the mingling of the sexes of both, and renewed vitality. 
It appears to the writer, and may appeal to the careful student 
of Dispersal, that whilst the main army, so to express it, ad- 
vanced rapidly and covered great expanses of ocean between 
Iceland and other more northern stations, and Bear Island and 
Faroe, and even further south still, the natural increase of the 
population of the St. Kilda colonies also caused an overflow of 
the population, which in its initiatory stages took a northerly 
direction ; and that those which wandered furthest to northward 
met the south-advancing host, and later became, as it were, 
overpowered, and ceased to penetrate much further, and thus 
an added impulse may well have been given to the more 
general advance. We should explain here that there cannot 
be any reasonable doubt about the increase of these birds 
at the St. Kilda group of islands during recent years, as there 
appears to be abundance of evidence of the fact. 
If the dispersal of these and other added colonies did take a 
northerly trend, and the superior forces met and overcame 
them, this may present a sufficient explanation of the great 
rapidity with which so many Scottish stations have been taken 
up since their earliest advent at Faroe in 1838, and Shetland 
in 1878. 
As regards the still further extensions to the west coast of 
Ireland, as related by Messrs. R. M. Barrington and Ussher,* 
that may also have been accelerated by the blending of blood and 
increased vigour; but, putting that aside, the Irish occupations 
may well be due to the direct influence of the greater southward 
general movement which appears to have taken place all over 
the North Atlantic. 
* ‘Trish Naturalist,’ September, 1911. 
