VOL. XV ] VALUE OF lJIUD-MAKKIN(i. \\9 



ill one or more parts of Northern Europe, and the comparative 

 \'akie of the subsequent records was thus much less certain 

 than in the case of records derived from birds all marked as 

 nestlings in a given area. 



After trials with smaller areas as the basis of classification, 

 thus estabhshing the absence of material local variations, 

 groups as wide as, say. " Lapwings marked as chicks in 

 Scotland and the North of England" were usually employed 

 in the end. Within a group such as this certain comparisons 

 were possible, as, for example, that some native Lapwings 

 remain throughout the winter while others emigrate, but 

 otlier large groups for comparison with this were unfortunately 

 lacking. The British Birds scheme"^' will be able to provide a 

 parallel group for the South of England : but, if it w^ere 

 feasible, one would also like to see similar studies carried 

 out in, for instance, Ireland, Holland, a district of France 

 and a district of Norway ; the basis would then exist for a 

 broad comparison that could scarcely fail to yield some of 

 the information which students of migration most earnestly 

 desire. 



It would, of course, be well if the records of the method 

 became sufficiently numerous to be quantitatively as well as 

 qualitatively significant, lending themselves to real statistical 

 treatment. Unfortunately the obstacles are very great, 

 although they may be sensibly diminished where the problem 

 takes the form of comparisons between sets of records 

 collected under approximately similar circumstances. The 

 number of birds in a given area at a given time is only 

 imperfectly represented by the mortality rate, because the 

 latter varies with time of year and other circumstances : the 

 true mortality rate, moreover, is still less adequately repre- 

 sented by the " recorded mortality " rate which forms the 

 datum of the method, because obviously a smaller proportion 

 of dead marked birds will be reported from some places or 

 countries than from others. There is virtue, too, in mere num- 

 bers of records, as may be seen from the following example : — 

 Out of 3,142 Lapwings marked, 62 were recovered, or 2.0 

 per cent. When the total was split up into groups according 

 to native districts or to years of marking, the separate per- 

 centages were found to vary from 0.4 to 3.3 in the groups 

 of 200 or more, and from 1.3 to 2.9 even in those groups 

 containing over 400. Obviously, therefore, no percentage 



* See Byitish Birds, Vol. X., pp. 217-18, for summary of Lapwing 

 I'ccords. — Eds. 



