INTERNAL MIGRATIONS 283 



observed over a great number of years, but the details 

 of the migration still remain to be worked out. From 

 what we have already learned of the emigration or 

 dispersal of birds, we cannot class Internal Migration 

 and Local Movement as fortuitous. 



A few words on Irruptic Movements will bring the 

 present chapter to a close. These movements are entirely 

 abnormal, and are rarely if ever attended by success. 

 One of the most remarkable instances of irruptic move- 

 n-.ent is that furnished by Pallas's Sand Grouse. Details 

 of the several irruptions of this species into Western 

 Europe (in every important invasion, however, be it 

 remarked, to increase breeding, not zviiiter area} need 

 not be given here; they are doubtless fresh in the minds 

 of most readers. The last great spasmodic invasion 

 which may be said to have spread almost entirely 

 over Europe took place in 18S8. The chief point 

 of interest to us, so far as the present subject is 

 concerned, is the absolute failure of these birds to 

 establish themselves in any portion of the area they 

 invaded. True, many of the birds made more or less 

 successful attempts to breed, and some individuals may 

 have lingered on in their new home for several years ; 

 but I much doubt if a single Sand Grouse out of the 

 thousands that invaded Europe in 1888 now survives. 

 Similar irruptions of Jays and Rose-coloured Pastors 

 have been remarked, but in no case has any permanent 

 success followed the movement. These movements 

 very forcibly demonstrate how futile irruptic colonization 

 is, and how rarely such individuals enter new areas where 

 conditions of life are favourable to them. They are 

 utterl}- abnormal means of dispersal, and in the great 



