I 146 ) 



A CKITICAL NOTE ON THE VALUE OF 

 BIRD-MARKING. 



BY 



A. LANDSBOROUGH THOMSON, o.b.e., m.a.. n.sc. 



The present writer has recently given elsewhere {Ibis, 1921, 

 p. 466) a summary of the results of a study of bird-migration 

 by the marking method, as carried on from the I'niversity 

 of Aberdeen from 1909 onwards . This inquiry was of necessity 

 brought to an end soon after the beginning of the war, 

 although a few co-operators were able to continue to use 

 their rings for some further years and reappearances were 

 still being recorded in very small numbers in 1920. An 

 extension of the work being impracticable, no course was open 

 but to make the best use of the data concerning the 27,802 

 birds marked and the 879 of these which were recovered. 

 In making his summary, however, the writer kept in view 

 the fact that much other work of the kind was still in progress, 

 notably that in connection with British Birds, and he accord- 

 ingly endeavoured especially to make some constructive 

 criticisms of the method and to assess the significance of the 

 kind of results which it is found to afford. It is on this 

 aspect of the subject that he has been asked to comment in 

 these pages. 



There are probably few who will deny that the method has 

 great possibihties and that in some directions the value of 

 its results has already been estabhshed. It must, of course, 

 always be regarded as supplementary to other means of study, 

 but while these deal with mass movements the marking 

 method singles out the individual bird and traces its part 

 in the wliole and thus, alter repeated confirmation, the part 

 played by birds belonging to a particular region of a species, 

 distribution. Clearly, this holds out hope of important 

 additions to our knowledge of the true nature of migration. 

 Nevertheless it must be admitted that the method involves 

 the expenditure of a great amount of time and labour, not 

 to mention money, and that the result is often very small 

 in proportion. The possibihties of getting birds marked 

 being naturally limited, the question arises as to whether 

 concentration on the more fruitful portions of the field of 

 inquiry is not the soundest pohcy. If this be admitted it 

 does not necessarily follow that a prehminary experiment 

 in working the w^hole field has not been justified. The question 

 is, rather, is not the experience of promiscuous marking now 



