XII 
THE COLOURS OF BIRDS 
249 
logical Observatory , gives numerous instances of this 
change occurring in birds, and distinguishes between 
cases in which the colour-change is associated with 
a change in feather-structure, and those in which it 
is not so associated. Thus in the linnet and mealy 
redpole, the surface of the barbs is said to peel off, 
exposing the fresh and bright colours beneath. In 
the case of the guillemot and little auks, on the 
other hand, he describes an increase in the amount 
of pigment in the feather without any textual 
change. Gatke enumerates numerous other instances 
of colour-change produced in this way by an in¬ 
creased amount of pigment, or by a rearrangement 
of pigment, as when black or blackish-brown replaces 
white or gray, or when black and white replace 
gray. 
A change of colour accompanied by a shedding 
of part of the feather seems not inexplicable, but 
the mechanism of a colour-change without this 
is difficult to understand, and the fact has been 
strenuously denied by many. A recent summary 
by Schenkling gives an account of the various 
opinions which have been held on the subject. 
Schenkling himself strongly inclines against the 
view that a notable colour-change can occur without 
a moult or a shedding of portions of the feathers. 
He believes that the confusion has arisen from the 
fact that the same moult has not identical effects 
upon all the individuals of a species, or even upon all 
the feathers of an individual. It is thus possible 
to obtain specimens displaying feathers apparently 
characteristic of successive moults. Such specimens 
have been described as birds showing colour-change 
