INTRODUCTION. XV1l 
The term Vernal Moult is used to signify the partial change 
of feather that particular species undergo, and that takes. 
place on the approach of the pairing season; which livery, 
as it were, remains only during that period. The moult is 
styled double in such species as are subject to the above-men-- 
tioned change. | 
In some cases, the male bird particularly is liable, though 
not to an actual change of feather, yet to a considerable va-. 
riation either in colour or brilliancy of hue on certain parts 
of the plumage, at the foregoing season. This variation has 
been attributed by Temmincx to the action of the air, and a 
gradual wearing away of the edges of the feather ; but I am 
sorry to be compelled, from the result of long continued ob- 
servation, to dissent from the opinion of so eminent a natura- 
list. I am induced to consider the plumage to be so far an 
actual part of the living bird, as to be under the influence of 
such constitutional change as the bird may at any time ex- 
perience, and such a change is strongly demonstrated at the 
season of pairing; witness its effects in the high degree of 
spirit frequently demonstrated, and in the superior song gene- 
rally called forth at this particular period. That there is an 
invisible circulating fluid pervading the feather, appears from 
the striking difference im elasticity and brilliancy of colour 
between the feather upon a bird whilst alive, and upon the 
same bird in but a short time after death, In water-birds, 
this principle of life in the feather (if 1 may be allowed the 
expression), is singularly apparent; as the plumage that is 
impervious to water upon the living bird, is almost imme- 
diately after death, subject to its effect. There can be 
no reason, then, why the feather may not be influenced 
