EXPLANATORY NOTE. 
In this work, of which the plan differs materially from 
that of any other on the same subject, the essential characters 
of the Orders, Families, Genera, and Species, being adapted 
for actual use, are given sufficiently in detail to enable the 
student to refer an object to its proper place. The very brief 
distinctive phrases which some naturalists affect, in imita- 
tion of Linnaeus, are practically useless. 
The characters of the Orders are short, those only which 
are general being given. Those of the Families are some- 
what more extended. It is to be understood that none of 
these characters are absolute, and that all the characters will 
not be found to agree precisely with every species of the Fa- 
mily or Order, although they refer to the greater number. 
The characters of the Genera are more precise, yet not ab- 
solute. Those of the Species, on the contrary, are strictly 
applicable only to the particular kind of bird referred to. 
These differences result simply from the fact that species 
only exist in nature, and that genera, families, orders, and 
all other groups, are merely ideal associations made for con- 
venience, and therefore more or less arbitrary. 
In the account which I give of each species will be 
found, first, a short comparative and distinctive description 
of the adult birds, or of the male and female separately, when 
they differ in colour or otherwise, and then of the young. 
This specific description is followed by some of the principal 
measurements of an adult male of ordinary size, namely — -1, 
the length from the tip of the bill to the tip of the longest 
feathers in the tail ; 2, the extent of a line drawn between 
the tips of the wings when stretched out ; 3, the length of 
the wing from the wrist-joint, or flexure, to the tip of the 
longest primary quill ; 4, the length of the bill measured 
along its upper outline, from the base to the tip, following 
its curve ; 5, the length of the tarsus ; 6, the length of the 
middle toe, or third toe, measured to the commencement of 
