204 Proceedings of the Koyal Physical Society. 



XXII. — The Possibilities of Bird- Marking, with special reference to 

 the Aberdeen University Bird- Migration Inquiry. By A. Lands- 

 borough Thomson, M.A., M.B.O.U. 



(Read 27th March 1911. Received 19th April 1911.) 



I. General. 



In this paper I propose to describe in outline the methods of bird-marking, 

 and to indicate the possibilities of that line of study : to that I shall add an 

 enumeration of the various bird-marking schemes that have been set on foot, 

 a number of examples of striking results achieved by these, and, finally, a 

 few notes on the work, plans and prospects of the Aberdeen University 

 Bird-Migration Inquiry. 



In its essentials the method consists in markino- a large number of birds 

 in some way or other, for the sake of the data afforded by the subsequent re- 

 appearance of a small proportion of these. The principle is identical with that 

 of the well-known method of marking fishes as a means of studying their 

 movements and life-histories. Various kinds of marks have been tried or 

 suggested in the case of birds : parchment tied under the tail with silk, thin 

 metal discs glued to the tail feathers, and indelible stamps on the tail 

 feathers. But all these, besides being clumsy, have the great disadvantage 

 of lasting only until the next moult. For both convenience and per- 

 manence, marks on the feet are obviously the best. In early, isolated 

 attempts at marking, such crude means as brass wire or silk thread twisted 

 round the bird's foot were used ; but in order to allow of an inscription, a 

 broad metal ring is necessary. As combining extreme lightness with a 

 considerable degree of durability, aluminium is to be preferred, and all the 

 more because it is easily worked and stamped. 



Complete rings, such as are used for homing pigeons, are of little use for 

 marking wild birds, as they can only be placed on very young birds in any 

 case, and not even then in the case of birds with nidifugous young, 

 these having well-developed feet by the time they are hatched. 

 Furthermore, such rings are expensive, as they are cut from 

 aluminium tubing instead of from sheet aluminium, and have 

 to be stamped when in circular shape instead of on the flat. 

 Hence the superiority in every way of the " split ring," which is a band 

 stamped from the sheet, and then folded into a circle. The edges are 

 merely pressed together, and such a ring, if of small diameter, will 

 keep its shape without difficulty. Rings of larger size must either be of 



