115 



when the colour changes from dull-black into gray again, there 

 does not seem to take place a noticeable growth of the horn, for 

 a number of old birds which stand in their autumn-moult or have 

 nearly finished it (received between 28 September and 8 November 

 1921), have got billheights of 13 to 15.4 as for the males (14 spe- 

 cimens) and 11.7 tot 14.6 as for the females (12 specimens). At the 

 same time as this growth of horn in spring, a changing of colour of the 

 bill takes place, just the same as with many other birds (compare 

 starling): the bill of the breedingdress is of a dull-black, the one 

 matching the winterdress of a horn-greyish colour. This last hue is 

 not the result of the wearing-out, the bird which at the end or 

 the summer begins moulting, has still got a dull-black bill. It 

 sometimes happens in spring that the bird, while already wearing its 

 breedingdress, has not got a black bill yet, but this is an exception. 

 A horhgrowth like the above described one, was noticed 'by Klein- 

 schmidt (1912) in Panis Salicariiis; he calls the bill in breeding- 

 time often „geradezu unförmlich lang und dick" and in the autumn 

 it is worn out again to „Normalgrösse". 



From the measures we also may conclude that the male as a 

 rule has a bill which is somewhat heavier than that of the female, 

 although the extremes perhaps are exactly the same. 



(Ingekomen bij de Redactie 3 Augustus 1922). 



Postscriptum.— On July 27th, 1922, I received .a Razorbill, 

 hatched summer 1921, which had died shortly before. The bird was 

 moulting from breeding- into winterdress, showing strong moult on 

 head, neck, breast, foreback and flanks, whereas belly and hindback 

 only showed a small number of growing feathers. It seemed full- 

 grown and the feathers of the old plumage — especially those of 

 the back — are very worn, as they are in all Guillemots and 

 Razorbills shortly before they begin moulting in summer, when most 

 of the bodyfeathers and the rectrices and remiges are a year old. 



As a one year old bird with very small testicles, this animal 

 ought to possess one or two billfurrows, that is to say the 

 white stripe only or the white stripe and one furrow and — as 

 the bird is in breedingdress — also the enlargement at the base 

 of the bill as it occurs in every Razorbill in breedingdress. The 

 bird misses however, except the enlargement at the base, every 

 furrow on the bill: the bill is just like that of a bird in its first winter. 



On July 28th, 1922, I found a second Razorbill, just driven 



