99 



The moult of Uria troille (L*) and Alca torda L* 



15 Y 



JAN A^ERWEY. 



The purpose of this investigation is to follow the changes in 

 moulting-time which present themselves in birds of the same species, 

 but differing in age, endeavouring at the same time to show the 

 connection between this moult, the corporal development and the 

 development of the genitals. 



Material and Methods. 



The material. Guillemots and Razorbills, furnished by the des- 

 tructions of seabirds on our coast by stormy weather and oil on 

 the water, principally answered both demands of the investigation : 



P The possibility of following the age of the birds for the first 

 three years of their life. 



2^ The disposal of many birds. 



I will try to explain furtheron how they answered the first point. 



As to the second point, I must confess that my material still was 

 insufficient though it amounted to about 450 Guillemots and about 

 130 Razorbills. The cause of this is that I always remained depen- 

 dent on the benevolence of the tides and on the terrible and 

 destroying pollution of the sea by costly quantities of oil. For 

 whereas on December 19th 1921 I received 71 and on January 11th 

 and 12th 1922 together 90 destroyed birds, the months November 

 and February — as well in the winter 20/21 as 21/22 — excelled 

 in peace for the birds and idleness for me. Besides it is necessary 

 for the autumn-moult, to examine birds from July, August and 

 September, birds which are only with difficulty to be got, as 

 Guillemots and Razorbills probably do not appear near our coast 

 in a somewhat important number before the end of August. 

 Destructions of larger numbers hardly ever take place before Sep- 

 tember and October, often not before November. 



The method of examination was rather simple. As long as a 

 bird's feather is not fullgrown, the calamus of dark feathers, on 

 examination of the inside of the skin, shows itself of a dark colour 



