BRITISH GENERAL MIGRATORY MOVEMENTS 583 



bird is noticed in a given area. When these observations are repeated for a number of years 

 by inany observers scattered over a considerable tract of country, they are useful. This is one 

 of the systems adopted by the committee of the British Ornithologists' Club, which for many 

 years has been accumulating valuable information about migration in England. 



2. The recording of observations made at the lighthouses and lightships round the coast 

 verified whenever possible by the wings of birds which have struck the lights. This work 

 was begun by the British Association Committee in 1883 and carried on for many years, and has 

 since been adopted by the B.O.C. Migration Committee. It has one drawback ; the best obser- 

 vations are those which are made during weather which is unfavourable to normal migration ; 

 at such times the birds are lured to the lights. 



3. The systematic observation, aided by collecting, of the visitors to any restricted area, 

 such as an outlying island which is a convenient resting-place for passage birds. The work of 

 Mr. Kagle Clarke and his helpers at Fair Island, St. Kilda, and the Flannans, and of the 

 Misses Rintoul and Baxter at the Isle of May, are sufficient proof of the efficacy of this method. 

 It has not only increased our knowledge, but has shown that many regular and irregular 

 movements take place about which, in former years, absolutely nothing was known. 



4. The collecting of records of rare birds killed by sportsmen, collectors, and others. The 

 destruction of these birds has been deplored, but it is foolish to refuse to add to knowledge by 

 disregarding the records. These records are to be found in most carefully prepared local faunas, 

 and have been ably summarised in the recently issued Hand-List. 1 



5. The marking of passage birds by means of numbered rings, and the tabulation of the 

 details of recoveries. This last system, practised on the Continent before it was adopted by 

 English and Scottish naturalists, though sometimes belittled as too slow and laborious a method 

 of obtaining information, is becoming one of the most important of the systems, for it is 

 demonstrating that many of the accepted theories are futile, and is providing indisputable facts 

 which will, when more are collected, supply data upon which sound theories can be based. 



III. CLASSIFICATION OF MOVEMENTS 



The movements may be classified according to season, breeding area, or the region beyond 

 our islands from which the birds travel. Whichever classification is adopted, there are a 

 number of species which cannot be described under a single heading, and some are represented 

 in several classes. This is well exemplified by such species as the rook, skylark, starling, and 

 swallow (vol. i. pp. 5, 200 ; vol. ii. pp. 105, 278). 



It may be accepted as an axiom that in the northern hemisphere migration is as a rule from 

 colder to warmer zones in autumn, and in the reverse direction in spring ; the avian movements 

 are more or less synchronal with those of the isotherms. Thus the general trend is from north 

 to south in autumn, south to north in spring. There are, however, certain clearly defined east 

 to west autumnal, and west to east vernal movements, which are especially noticeable in the 

 south-east of England. The birds come to winter in the warmer though not necessarily more 

 southern part of their range. 



The seasonal movements are as follows : 



1 A Hand-List of British Birds, Hartert, Jourdain, Ticehurst, and Witherby, 1912. 



