INTRODUCTION. 3 



support from observations of a few airmen during the war; I 

 am convinced that large numbers of birds frequently if not 

 regularly pass over our islands at too great a height for normal 

 observation, assisted, especially in autumn, by cyclonic move- 

 ments — in fact, carried on the wind. When meteorological condi- 

 tions fail or physical strength is overstrained, parties or individuals 

 drop to a lower altitude and alight ; it is thus that the list of 

 rarer visitors is swelled. The birds which reach our shores, 

 wearied or dying, or which crowd round coastwise lights, coming 

 in against the wind, are contending with unforeseen adverse 

 circumstances. Visible migration is seldom normal migration. 

 Only by some such theory can we explain the repeated 

 occurrence of unfamiliar species on such isolated rocks as Fair 

 Island and St. Kilda, unless we accept the unlikely supposition 

 that every autumn vast numbers of birds migrate westward to 

 perish in the Atlantic, a few finding a temporary asylum on 

 these islands. The fact that many of these birds are met with in 

 the same places in spring cannot be explained in this way. 



It is an extraordinary fact that, although all ornithologists are 

 interested in migration and for centuries field naturalists have 

 been keeping notes of the arrival and departure of birds, we 

 still know very little about actual times and seasons. Formerly 

 it was not uncommon to find the statement that this or that 

 species arrived or departed on or about a particular day of the 

 month ; there are still recorders who give one date as the 

 average. As a matter of fact, birds are more variable in their 

 habits than is generally admitted. Certainly within recent 

 years we have had many earlier and later dates recorded than 

 are given in most text-books. This to some extent is due to an 

 increased interest in birds, extended now to the younger folk 

 through the medium of education, and to the fact that the Press 

 has realised that natural history is popular. A considerable 

 amount of unreliable " knowledge " is now circulated. There are 

 nature students and field naturalists who are so keen about 



