INTRODUCTION xi. 



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, is 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 % c > 

 colour-change until maturity is reached ; it therefore f^ ai 

 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. 



