P. H. BAHR: THE BLACK-HEADED GULL. Ill 



During the spring of this year (1909) I have had three 

 individuals under close observation — two mature birds 

 and a young bird received in 1907, which this year for 

 the first time assumed the black hood. No change of 

 any sort was observed till the middle of March, when 

 they completed the moult in a fortnight. 



Those feathers mounted for microscopical examination 

 showed the usual changes preliminary to moult, and 

 a complete series of developing black feathers. No 

 invasion of the shaft of the old feathers with pigment, 

 which would undoubtedly take place in colour-change, 

 was noted. Till April 5th feathers from the vertex 

 and chin were observed to have the terminal rami broken 

 off and the softer basal ones gradually stripping off 

 from the shaft. This was especially noticeable in those 

 from under the chin, where many of the white feathers 

 were only represented by a calamus having a terminal 

 tuft of rami. The complete new black feathers from 

 the crown differed considerably from the old ones in the 

 same situation in being shorter, more compact and round, 

 and the rami were provided with longer and stouter 

 radii. These, in short, were the main changes observed 

 in a large number of specimens. The process seemingly 

 being that the rami at the base of the feathers strip off 

 as the new one pushes its way underneath. 



The conclusions I have arrived at are as follow : — 



(1) That individuals vary in the amount of black on 

 the crown in the winter plumage, and that this variation 

 has given rise to the belief that a " colour-change " takes 

 place. 



(2) That no colour-change occurs. 



(3) That a moult takes place usually about the 

 beginning of February, and under natural conditions 

 takes about a week to complete, and that it not only 

 embraces the head but the breast and back as well. 



(4) That birds of the previous year occasionally assume 

 the black hood of the breeding plumage, while retaining 

 the immature dress on back and wings. 



