INTRODUCTION. 



figure also has been given wherever a very marked differ- 

 ence exists between the two sexes ; and where this measure 

 has not been adopted with respect to the variations incident 

 to season, they have still been studiously pointed out in the 

 description of the species. 



In the course of the descriptions, the terms vernal (or 

 spring) and autumnal (or general) moult frequently occur; 

 which it appears necessary to explain. By the Autumanl 

 Moult is meant that entire annual change of plumage to 

 which all birds are liable, and which usually takes place at 

 this time of the year, or after the production of the species*. 

 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- 

 mentioned 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 TEMMINCK to the action of the air, and a 

 gradual wearing away of the edges of the feathers ; but I am 

 sorry to be compelled, from the result of long continued ob- 

 servation, to dissent from the opinion of so eminent a natu- 

 ralist. I am induced to consider the plumage to be so far 

 an actual part of the living bird, as to be under the in- 



* In the Swallow tribe, and some few others, it happens at a later pe- 

 riod, or during the months of January or February. 



