INTRODUCTION >a 
In most species it seems hardly necessary to refer to 
the axillaries, seeing that they are usually whitish in colour, 
but where these feathers form a distinguishing feature (e.g., 
the black axillaries of the Grey Plover, or the black and 
white ‘ barring’ on the same feathers of the Green Sand- 
piper, Plate XXXV.), they are described. In like manner 
the down of the nestling, which is usually variegated 
with different shades of yellow, brown, and black, 1s not 
described ; the reader’s attention is directed only to curious 
forms, such as the stripes of the nestling Grebe and the 
sooty-black shade of the young Corn-Crake. 
Generally speaking, the irides of birds undergo a gradual Eye, 
colour-change until maturity is reached ; it therefore ee and 
seems unnecessary to describe other than the colour of the 
irides of the perfectly mature bird. While the foregoing 
remarks also apply to the beak and feet, the tints of these 
sometimes vary in adults at different seasons of the year ; 
thus it is to be understood that such colours refer only to 
the conditions found when the nuptial plumage is assumed. 
The voice-syllables are most difficult to describe on Voice. 
paper, and no doubt are best expressed in terms of musical 
notation; even then it is necessary to refer the notes to 
special forms of instruments, on which the characteristic 
pitch, tone, and volume, can be reproduced. Still, in a 
given call-note or in an alarm-cry, the number of syllables, 
their rapid or slow succession, their repetition, and the way 
in which they are accentuated, are points which generally 
can be appreciated on paper without musical aid. It is 
to be hoped that attempts to describe the voices of birds 
on these lines may prove of some use to the reader when 
he goes afield. 
In describing some species it has been found advan- 
tageous to compare them with certain others with which 
they might easily be confounded. This is well seen in the 
case of the darker-plumed ducks, which usually can be 
observed only at a distance with a binocular. 
