481 
1921.] Bird-Migration by the Marking Method. 
from other sources where special opportunities for obtaining 
records do not enter into the question. 
In the sections which follow the comparisons made with 
the results of other investigators are by no means exhaustive. 
The species successfully studied abroad are for the most part 
unimportant in this country, so far as records go, and the 
results of the 4 British Birds ’ inquiry (26), which are the most 
important for this purpose, have as yet been published in 
collected form only in the case of a very few species. 
The Numbers oe Birds marked during the 
Aberdeen University Inquiry. 
Table I. shows the total numbers of birds of different 
species marked during the course of the investigation. In 
the third column the number of reappearance records is 
given, and in the fourth column the percentage of marked 
birds which have reappeared. The figures may be regarded 
as complete for all practical purposes, as additional records 
have, at the time of writing, become very infrequent. From 
the numbers and percentages of reappearance records the 
following are excluded :— 
(a) Records of birds recovered at the same place on the 
day of marking, or, in the case of young birds, 
within the flightless period; 
(b) Incomplete and faulty records which have not been 
considered sufficiently well established to be in¬ 
cluded among the results ; 
(c) Second and subsequent records for the same bird. 
The percentage is not calculated for species of which less 
than fifty individuals were marked, and it should be accepted 
with reserve in cases where the total is less than some 
hundreds. 
Detailed summaries of the numbers marked are given in 
the case of certain of the more important species discussed 
at length in the subsequent pages. 
