106 BRITISH BIRDS. 



three young birds of the year reared by hand. They 

 were all kept in a wired compartment, and carefully 

 examined every week. The heads of the marked birds 

 were drawn to scale, and the amount of colouring noted 

 once every week. In order to identify individual 

 feathers certain of them were stained red with carbol 

 fuchsin and indicated on the diagram, so that they could 

 be recognised again in order to ascertain whether any 

 colour-change was actually taking place in them or no. 

 Two or more feathers were extracted and mounted on 

 slides and examined microscopically every week. 



The result of the inquiry goes to prove, I venture to 

 think, that no such thing as colour-change occurs in 

 this species before the moult at least, and that the black 

 head is gradually assumed by growth of the new black 

 feathers beneath the white ones of the winter dress. 

 One circumstance which vitiates the experiment is that 

 being kept in close confinement and living under 

 unnatural circumstances, the onset and duration of the 

 moult was delayed. In the immature wild bird no change 

 of any description was noted in the head or neck, though 

 the brown feathers on the back and wing were gradually 

 lost. The immature birds raised by hand had a complete 

 body-moult in January, but no indication of any black 

 feathers on the head was observed. However, birds in 

 immature plumage do occasionally assume the black 

 hood ; two very good examples were to be seen in the 

 Zoological Gardens during the spring of 1908. 



In the wild state the spring plumage is often assumed 

 early in January, but more frequently in early February. 

 From observations made during the spring of this year 

 on London Bridge, where the birds come so close that 

 each step in the change may be observed at close range, 

 I found the moult takes about a week to complete. 



Minute observations on my birds began on January 

 19th, 1908. Fig. 1 shows how the heads of the three 

 adult marked birds then appeared. The charted diagrams 

 made every week showed no change till March 29th, 



