478 Dr. A. L. Thomson : Results of a Study of [Ibis, 
accordance with the districts in which the birds were 
marked, as is explained more fully in Section II. : a dis¬ 
tinction has also been maintained between birds marked 
when young and birds obtained under other circumstances, 
the latter class being further sub-divided under seasonal 
headings. The object in view has been to keep together 
records relating to birds originally belonging to presumably 
homogeneous groups, and in this way to eliminate errors 
due to possible geographical differences. But where the 
grouping has revealed no marked divergency, the separate 
treatment of the groups is abandoned. 
The data thus grouped have been analysed, as a rule, in 
three different ways. The principal analysis is a seasonal 
one, the reappearance records of all birds of a particular 
group, or series of similar groups, being classified according 
to locality and calendar month. In this main analysis the 
records of birds recovered in their first, second or subsequent 
seasons, are treated alike : to exclude any error from this 
source a second analysis is added in which the classification 
is by localities and ages. The third analysis is similar to 
the second, but is based on the calendar year (reckoned 
from summer to summer) instead of on the year of the 
bird’s life, and it thus affords a check on possible errors 
due to meteorological differences between one winter and 
another. The fulness with which the grouping and 
analyses have been published will be found to vary with 
the circumstances. 
A further section of the report contains a series of brief 
summaries of the records relating to those species for which 
the data are insufficient to warrant any more elaborate 
treatment. Many of these summaries, however, contain 
more or less isolated records which are of some interest 
despite the danger that lies in too much importance being 
attached to occurrences which may possibly be exceptional. 
The possibility of entirely exceptional individual movements 
being recorded by the marking method is indeed a point 
which must constantly be borne in mind by students of the 
