524 
Dr. A. L. Thomson : Results of a Study of [Ibis, 
XII.—CONCLUSIONS REGARDING THE VALUE OF THE 
METHOD OF BIRD-MARKING. 
It is thought that the results and conclusions set forth in 
the preceding sections, together with the data collected by 
other workers, will be considered sufficient proof of the 
value of the marking method as a means of obtaining a certain 
type of fact regarding the problems of bird-migration. At 
the same time it will be evident that the labour involved is 
very great and that the percentage of marked birds recovered 
is generally very small, while the results are in some cases 
largely invalidated by inherent defects which the method 
displays under certain circumstances. Various reservations 
must accordingly now be made in appraising the method, 
and the conclusion that must be drawn is that it would be 
advisable to restrict its further practice to those lines which 
have been shown to be comparatively fruitful in reliable 
and interesting results. 
The continuance of promiscuous marking is likely, of 
course, to yield a small proportion of isolated results that 
will possess an undoubted interest. But it is questionable 
whether records of this kind will ever adequately repay the 
time, labour,, and money expended on the actual task of 
marking. Certainly these records will not equal in value 
the results which can be obtained by more systematic study 
on restricted and carefully selected lines. 
It has been stated in the introduction that three qualities 
were considered essential, on a priori grounds, before a 
species could be regarded as a suitable subject for this kind 
of study : it must be available for marking in large numbers, 
it must afford a good percentage of reappearance records, 
and its migratory movements must present features worthy 
of investigation. To these may now be added a fourth point, 
namely that the circumstances must be such as will not tend 
to invalidate the results by the introduction of too many 
uncertain elements. 
Quantitative as well as qualitative analysis must be aimed at 
in spite of the obstacles that seem to lie in the way. As has 
