PREFACE. 
Having brought this my second Monograph to a close, I am led to hope that my 
labours 
the elucidation of a tribe of birds hitherto involved 
much confusion, will 
not be destitute of 
deg 
of value, more especially 
the 
eyes 
of 
nitholog 
introducing to their notice as it does many new species, and clearing up the difficulties 
with which many of those even common in our cabinets have been previously sur- 
rounded, — difficulties arising from several causes, among which may be enumerated the 
differences in plumage, which obtain so often between the males and females, as well 
as between the young males and the adults of the same sex, in some of the minor 
groups ; to which may be added the circumstance of the subject not having been at- 
tempted by naturalists possessing command of those ample resources necessary for extri- 
cating the subject from the labyrinth of confusion in which it has long been involved. 
It would be presumptuous in me to say that this monograph is fully completed, or 
that I have figured every existing species ; on the contrary, I have reason to believe 
that many will yet be discovered, both in the Old and New World, particularly in 
those remote regions which civilized man has seldom, if ever, visited : but in order to 
render the work complete up to the present time, I have not only done my utmost to 
add every species to my own collection, but have visited all the principal Museums of 
Europe, both public and private, and, as in previous instances, have experienced the 
greatest kindness and cooperation from the various eminent naturalists, private indivi- 
duals, and the officers of the natural history department of every public institution. 
