Introduction: Variation. Q^ 



The moult. — In the temperate and cold regions of the northern hemisphere 

 it is generally admitted that a complete moult takes place in birds in autumn 

 after the breeding season ; many species moult again in spring, and some a third 

 time in summer. The principal time for moulting in Celebes, Sangi, 

 and Talaut seems to be from July to December, when the birds probably 

 undergo a complete post-nuptial moult. It is questionable whether signs of a spring 

 moult can be found; on the other hand some species may be found moulting 

 during most months of the year. For instance, specimens in the Dresden 

 Museum of Heteractitis brevipes are moulting in January, April, July, August, 

 November; of Actitis hi/poleucos in January, March, July, November. 



Some of the Waders, autumn visitors from the North to Celebes [Aegialitis 

 geoffroyi, Heteractitis)., seem to moult first on the under parts, then the remiges, 

 and finally on the upper surface. No regular order in moulting is pursued in 

 the Black Sunbirds [Hermotimia], among which the transition from young to adult 

 male dress can be particularly well observed. The characteristic metallic sub- 

 gular stripe of the Celebesian species makes its appearance first, but the rest 

 of the plumage is developed without any such regular sequence, and there is a 

 specimen of Hermotimia talaiitensis in the Dresden Museum (C 15377) in almost 

 complete adult dress except on the forehead and crown, while a second of the 

 same species (C 13 847) has the plumage of the adult on the forehead and most 

 of the crown, but the young dress on most of the other parts. This proves 

 that the transition from the young to the adult dress does not take place in 

 perfect phylogenetic order; that is, the adult characters are not necessarily 

 developed in the young male bird in exactly the same sequence as 

 that in which they were acquired in the evolution of the race (see, 

 also, immature male, pp. 469, 471). 



Besides their feathers some birds are known to shed certain corneous 

 appendages or coverings on their bills; for instance, the white Pelican of 

 America has a horny knob on the culmen during the breeding season, but 

 which falls off when that period is over; and the Puffin [Fratercula) moults the 

 horny sheath of its bill and the outgrowths over the eyes (Newton, D. B., 

 pp. 599, 600). It is possible that a similar moult of the ribbed plates at the 

 base of the bill of the Celebesian Hornbill, Cranorrhinus cassidix, takes place. 

 It is believed by the natives to add one rib-plate each year; and, though this 

 notion is certainly wrong, it is possible that a shedding of the plates has been 

 observed. 



Change of coloration without a moult. — In a recent number of the "Auk" 

 (1897, April) Dr. Chadbourne has furnished what seems to be the first really 

 conclusive evidence that a change of colour may take place in the perfect 

 feather, this being caused by a redistribution of the pigments already present 

 in the shaft and barbs. The observations were made on the male Bobolink, 

 Dolichonyx oryzivorus (L.), but there can be now no doubt that the principle is 



