VOL. XV.] VALUE OF BIRD-MARKING. 147 



sufficient to show how further effort may be concentrated 

 in such a manner as wih lead to results of the maximum value ? 

 In the writer's opjinion, the best prospects of the method lie 

 in certain definite directions, and continued diversion of 

 effort into minor channels thus seems to him likely to diminish 

 or retard the chances of obtaining the valuable results which 

 some measure of concentration might well achieve. 



There would appear to be two broad classes of results 

 which marking may yield, and these may be roughly described 

 as individual and cumulative. In the first class may be 

 placed records such as those of British-bred Swallows from 

 South Africa {British Birds), records which estabhsh a new- 

 fact of great interest but which seem unlikely ever to become 

 sufficiently numerous to afford a basis for detailed analysis. 

 Records of this kind enable one to say that such and such 

 sometimes occurs, but for an attack on the fundamental 

 problems of migration one requires data from which one 

 can infer that such and such is the rule or occurs to a certain 

 definite extent. From the point of view of the great biological 

 questions of migration, as distinct from the histories of 

 particular species, the second kind of record is needed, records 

 which fit in with many others to give a more complete picture 

 of some selected phenomenon of migration. This kind of 

 record is to be obtained, whether by special concentration 

 of effort or not, from marking the more " remunerative " 

 species on a large scale and in a systematic manner. 



If the object be to gather individual records about as many 

 different species as possible, promiscuous marking will 

 obviously suffice ; but if it be agreed that the nature of 

 migration is the more important study, it will follow that 

 the most valuable results are those which help to build up a 

 thorough knowledge of some particular examples. On the 

 Continent considerable success has attended the intensive 

 study of such species as the White Stork, the Hooded Crow 

 and the Teal (although the selection may have been guided 

 by chance rather than by intention), and in working out the 

 Aberdeen University data the writer has found greater interest 

 and promise among the numerous records of, say, the Lapwing 

 than in any equal number of records scattered among various 

 species which have each contributed only a few to the total ; 

 the experience of the British Birds scheme, when the time 

 comes for final analysis, is not likety to be very different. 



x^ssuming the desirability of concentration, the question 

 arises as to how far experience now affords a basis for selection. 

 Two requirements nuist, from the outset, obviously be fulfilled 



